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Effect of different doped elements on visible light absorption and ultraviolet light emission on Er3+:Y3Al5O12
Journal of Luminescence 132 (2012) 3010–3018
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Effect of different doped elements on visible light absorption and ultraviolet light emission on Er3 þ :Y3Al5O12 Linuan Yin a, Ying Li a, Jun Wang a,n, Yu Zhai a, Yumei Kong b, Jingqun Gao a, Guangxi Han a, Ping Fan a,n a b
College of Chemistry, Liaoning University, Shenyang 110036, PR China College of Pharmacy, Liaoning University, Shenyang 110036, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 December 2011 Received in revised form 3 June 2012 Accepted 15 June 2012 Available online 26 June 2012
In this progress report, seven kinds of novel carefully designed and fabricated up-conversion luminescence agents, Er3 þ :Y3Al5O12, Er3 þ :YbnY3 nAl5O12, Er3 þ :Y3BaAl5 aO12, Er3 þ :Y3GabAl5 bO12, Er3 þ :Y3Al5NxO12 x, Er3 þ :Y3Al5FyO12 y and Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y, are successfully synthesized using sol–gel methods. After that, their corresponding photocatalysts, Er3 þ :Y3Al5O12/TiO2, Er3 þ :YbnY3 nAl5O12/TiO2, Er3 þ :Y3BaAl5 aO12/TiO2, Er3 þ :Y3GabAl5 bO12/TiO2, Er3 þ :Y3Al5NxO12 x/TiO2, Er3 þ :Y3Al5FyO12 y/TiO2 and Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2, are also prepared by sol–gel coating process. The obtained up-conversion luminescence agents and photocatalysts were characterized by using XRD, XPS, SEM, UV–vis and fluorescence spectrophotometer. Synchronously, several kinds of organic dyes are used to test their photocatalytic degradation using prepared photocatalysts. It indicates that the up-conversion luminescence ability of Er3 þ :Y3Al5O12 can be improved obviously through doping of some elements. And then, the photocatalytic activity of TiO2 is markedly enhanced by modified up-conversion luminescence agents which can transform much visible light into ultraviolet light. & 2012 Elsevier B.V. All rights reserved.
Keywords: Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y Up-conversion luminescence Effect of doped elements Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/ TiO2 Photocatalytic activity
1. Introduction In recent years, exploring new energy and material is attracting much attention for the contamination of environment, particularly, the use of solar energy appeals to many researchers [1–3]. TiO2 as a n-type semiconductor material plays an important role in removal of organic pollutants and use of solar power generation [4]. Its widely application is due to biological and chemical long-term stability, strong oxidizing power, low cost, against photocorrosion and chemical corrosion [5–8]. However, a general problem in use of TiO2 systems is the limited absorption spectrum. TiO2 absorbs strongly only during ultraviolet light below wavelength 387 nm [9], which limits the utilization of visible light sufficiently and leads to lower efficiency and high costs on utilizing TiO2. Er3 þ :Y3Al5O12 is a promising up-conversion luminescence agent precursor and can make visible light translate into ultraviolet light [10–12]. In our previous work, Er3 þ :Y3Al5O12/TiO2 composites had been studied in detail [13,14]. The changes of the corresponding spectra in the Er3 þ :Y3Al5O12 following the absorption of visible light and emission of ultraviolet light illustrate the high up-conversion activity. Hence, the TiO2 composite with
n
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up-conversion luminescence agent can make use of solar light efficiently. In the communication, for example, it becomes a reality to use ZnO–TiO2 coating Er3 þ :Y3Al5O12 in solar cell and dyes degradation under solar light irradiation [15]. The reason for this application, on the one hand, is largely because of their unique intra 4f transition [16]. On the other hand, it is due to the particular characters of TiO2 and ZnO, which possess superior photoreactivity, nontoxicity and long term stability. When the proportion of Er3 þ is 1.0 at%, the up-conversion efficiency of Er3 þ :Y3Al5O12 is high enough [17,18]. The photocatalytic activity of Fe and Co-doped TiO2 in degradation of organic dyes is obviously enhanced by Er3 þ :YAlO3 [19]. Nevertheless, the ultraviolet light (l o387 nm) generated by the Er3 þ :Y3Al5O12 is not sufficiently absorbed by TiO2. Mainly, Er3 þ :Y3Al5O12 is constrained by its narrow absorption spectra and weak excitation spectra [20]. In order to effectively utilize solar energy for environmental pollution control and solar electrical energy generation, it is urgent to further enhance the up-conversion luminescence efficiency of Er3 þ :Y3Al5O12. Perhaps, the doping of other ions into Er3 þ :Y3Al5O12 can improve the upconversion luminescence. According to the reports, up-conversion intensity can become strong due to Pr doping Er3 þ :Y3Al5O12 [21,22], but the absorption and emission spectra are still narrow. The infrared light is translated into visible light with Yb3 þ doping Er3 þ :Y3Al5O12 [23–25], which can also enhance the up-conversion ability of Er3 þ :Y3Al5O12. The up-conversion luminescence
L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
can take place with B doping Y3Al5O12 [26], including K2Al2B2O7 [27] and YAl3B4O12 [28]. Among them, K2Al2B2O7 makes the visible light translate into ultraviolet light. Jia et al. made a research on Y3GaxAl5 xO12 films doped with rare earth ion [29], which shows good luminescence property. The strong ultraviolet light can also be detected from Yb3 þ /Tm3 þ co-doped LiYF4, BaYF5 and NaYF4 [30–33]. It turned out to be a great improvement for the past work, but the spectrum range is still unsatisfied. Thus, the utilization of solar energy by up-conversion luminescence is limited still. To compensate the disadvantage of up-conversion luminescence agent, in this work, through systematically doping other ions we tried to widen the spectrum range. That is, doping Yb, B, Ga, N and F makes the absorption spectrum range and emission spectrum intensity of Er3 þ :Y3Al5O12 enlarge much. Theoretically, these doping ions can change the crystal field and energy level around the central Er ion in a way. Concretely, the purpose to dope Yb is to sensitize Er3 þ :Y3Al5O12 and enhance the upconversion activity. Further, up-conversion and emission scopes are rationally enlarged through doped ions with defined concentrations. Al is replaced by B and Ga atoms, which have small and big ionic diameter compared with Al, respectively, to enhance the visible light absorption range and ultraviolet light emission intensity. For this reason, as e/r changing great, the intensity of crystal field inside will be transformed. In the same way, N and F are used to replace O in order to enhance the absorption and emission extent, for their different electronegativity and radius from O atom. The improvement of up-conversion ability of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y might be attributed to the presence of Yb, B, Ga, N and F. It supposed that the Er3 þ : YbnY3 nBaGabAl5 a bNxFyO12 x y would become a great promising up-conversion luminescence system. In this paper, we reported that some elements were used to dope into Er3 þ :Y3Al5O12 and then coated by TiO2 film to form novel photocatalysts. That is, several new up-conversion luminescence agents and corresponding photocatalysts with excellent performance are prepared by a simple sol–gel procedure. Structural properties were studied by X-ray powder diffractometer (XRD). Grain sizes have been calculated and estimated based on the XRD patterns and SEM images. The category and amount of doping ions were detected by XPS. Decay curves of absorption and emission spectra have been recorded and analyzed using UV–vis and fluorescence spectrophotometer. And then, the photocatalytic performance of different TiO2 coated composites of Er3 þ :Y3Al5O12 doping with Yb, B, Ga, N and F was studied through the degradation of some organic dyes under solar light irradiation. The results indicate these modified up-conversion luminescence agent have the additional advantage of widening and intensifying up-conversion spectra, thus opening up vast opportunities for solar cell and sewerage treatment. We believe that the enormous improvement of the up-conversion efficiency of these up-conversion luminescence materials opens the door for future applications in the field of solar cell.
2. Experimental
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powders were dissolved in HNO3 (65%, Veking Company, China) with magnetic stirring and heating until transparent. 2.9566 g Al(NO3)3 9H2O (99.99%, Veking Company, China) was dissolved in 30 mL distilled water. At room temperature, the aqueous solution of aluminum nitrate solution was introduced slowly into the rare earth metal ion solutions under vigorous stirring. Then 8.0301 g citric acid (C6H8O7 H2O, 99.99%) was added as chelating agent and assistant solvent, in a molar ratio of citric acid:metalion¼ 3:1. Then the remaining solution was stirred and heated at 50–60 1C until the transparent solution was successfully prepared. In the process of drying, no deposit was formed until all solvent was evaporated and the foamy gel was finally obtained. Afterwards, the gel was heated at 80 1C and ground into fine homogeneous powders. The collected powders were heated at 500 1C for 50 min, and then kept at 1100 1C for 2.0 h. At last, the sintered substance was taken out of the tube furnace and allowed to cool down to the room temperature in atmosphere. Then, the desired white Er3 þ :Yb0.4Y2.6Al5O12 powder was obtained. The synthesis methods of Er3þ :Y3Al5O12, Er3þ :Y3BaAl5 aO12 (a¼1.25–2.50), Er3 þ :Y3GabAl5 bO12 (b¼1.25–2.50), Er3 þ :Y3Al5 NxO12 x (x¼0.005–0.010), Er3þ :Y3Al5FyO12 y (y¼0.005–0.010) and Er3 þ :Yb3 nYnGaaBbAl5 a bNxFyO12 x y (n¼0.0–0.4, a¼b¼1.25– 2.50, x¼y¼0.005–0.010) were similar to above mentioned. In order to prevent the volatilization of H3BO3, ethanediamine (C2H8N2) and HF, they were added after the solution was neutral and transparent. 2.2. Preparation of Er3 þ :YbnY3 nGaaBbAl5 a bNxFyO12 x y/TiO2 Take Er3þ :Yb0.3Y2.7Al5O12/TiO2 for example, Er3 þ :Yb0.3Y2.7Al5O12/ TiO2 composite was prepared through the ultrasonic dispersion and sol–gel method [35]. The molar ratio of Ti(O–Bu)4:ethanol:H2O:acetic acid was controlled at 1:10:2:1 and the final quality ratio of TiO2 and Er3 þ :Yb0.3Y2.7Al5O12 was controlled at 1.0:0.3. At first, through treating a suspension of Er3 þ :Yb0.3Y2.7Al5O12 particle in an ultrasonic bath for 10 min the transparent colloidal solution containing 1.0 wt% Er3 þ :Yb0.3Y2.7Al5O12 was obtained. Second, a homogeneous solution of Ti(O–Bu)4 in ethanol was used as titanium dioxide precursor. The mixed solution of ethanol, acetic acid and deionized water were gradually added into above solution under stirring magnetically. The final pH value of solution was about 3.0. After 10 min stirring, 0.3000 g Er3 þ : Yb0.3Y2.7Al5O12 colloidal solutions were added into the final solution with stirring until to gel. The gel was heated to 120 1C in oven and kept at constant temperature for 120 min. Afterwards, the temperature was controlled at 500 1C for 60 min. Finally, the Er3 þ :Yb0.3Y2.7Al5O12/TiO2 composite particles were obtained. The synthesis method of Er3þ :Y3Al5O12/TiO2, Er3 þ :Y3BaAl5 aO12/ TiO2 (a¼1.25–2.50), Er3þ :Y3GabAl5 bO12/TiO2 (b¼1.25–2.50), Er3 þ : Y3Al5NxO12 x/TiO2 (x¼0.005–0.010), Er3 þ :Y3Al5FyO12 y/TiO2 (y¼ 0.005–0.010) and Er3 þ :Yb3 nYnGaaBbAl5 a bNxFyO12 x y/TiO2 (n¼ 0.0–0.4, a¼b¼1.25–2.50, x¼y¼ 0.005–0.010) were the same as mentioned above. 2.3. Characterization of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y and corresponding Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2 photocatalysts
2.1. Synthesis of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y Er3 þ :YbnY3 nAl5O12 (n ¼0.00–0.40 at 0.10 intervals) doped with Yb3 þ ion were synthesized via sol–gel procedure in the presence of citric acid (C6H8O7 H2O, 99.99%, Veking Company, China) as chelating agent according to the following process [34]. Take Er3 þ :Yb0.4Y2.6Al5O12 for example, 0.0031 g Er2O3 (99.99%, Veking Company, China), 0.1255 g Yb2O3 (99.99%, Veking Company, China) and 0.4650 g Y2O3 (99.99%, Veking Company, China)
For confirming the formation of anatase phase and estimating the proportion of different crystalline phases, the X-ray powder diffraction (XRD) patterns were determined by X-ray powder diffractometer (D-8, Bruker-axs, Germany) using Ni-filtered Cu Ka radiation in the range of 2y from 101 to 701. Scanning electron microscopy (SEM, JEOLJSM-5610LV, Hitachi Corporation, Japan) was used to detect the morphology of particles. Fluorescence spectrophotometer (FLSP920, Edinburgh Instruments, UK) was
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adopted to detect the emission spectra of Er3 þ :YnYb3 nGaaBb Al5 a bNxFyO12 x y. And the UV–vis spectrometer (LAMBDA-17, Perkin–Elmer Company, USA) was applied to judge the excitation wavelength of up-conversion luminescence agents and degradation ratios of dyes in aqueous solutions. 2.4. Investigation of solar photocatalytic activity of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y The evaluation of photocatalytic activity of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y/TiO2 composites heat-treated at 500 1C for 60 min was carried out through the degradation of some organic dyes under given conditions such as 10 mg/L initial concentration, 1000 mg/L photocatalyst addition amount and 100 mL total volume except special demand. The dye suspensions were irradiated by solar light after agitation in dark for 30 min. Then, the suspensions were sampled at specific intervals to determine the changes of dye concentration. The sampled suspensions were centrifuged three times at 4000 rpm for 30 min to obtain the clear solution. The UV–vis spectrometer was used to analyze the degradation ratio of the dye solution.
3. Results and discussion 3.1. XRD, SEM and XPS of Er3 þ :YbnY3 nBaGabAl5 a bNxFiO12 x y The prepared samples were investigated by powder X-ray diffractometer (XRD) over the 2y range between 101 and 701. Fig. 1 intriguingly shows the changes of different Er3 þ :YbnY3 nBaGab Al5 a bNxFyO12 x y powders in XRD patterns. By and large, various doped ions seem to enhance their diffraction peak intensities. The main characteristic peaks are displayed at 2y ¼18.121 (211), 33.361 (400), 42.581 (422), 46.621 (521) and 55.121 (532) in all given Fig. 1, which indicates the presence of elementary Er3þ :Y3Al5O12 composition. Fig. 1a(1–6) shows the peak characters of different up-conversion luminescence agents. It can be seen that doping ions make peaks change a little both in peak intensity and position. Fig. 1b(1–5) shows
that the characteristic diffraction peaks slightly sharpen along with the increase of Yb doping quantity [36], and no change in phase composite, but few changes can be found when n40.30. It can be concluded that the crystal shape tends to stabilize at n40.30. The stronger peaks appear at 2y ¼33.381, 33.401, 32.941, 33.461 and 33.401, but becomes less than that at 2y ¼33.551 (400) [20]. Because the doping amount of B, Ga, N and F is small, the characteristic peaks shift only a little. There are a few of differences among different upconversion luminescence agents, which suggests the structure of upconversion luminescence agents will not greatly change by doping other ions. It is worth noting that the peak width of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y is wider than that of Er3 þ :Y3Al5O12. It has the similar tendency with Ga, N and F doping Er3þ :Y3Al5O12 shown in Fig. 1(d–f). The peak of Er3þ :Y3BaAl5 aO12 is different from others. As described in Fig. 1c(1–2), the more the doping amount of B the weaker the peaks become. And a new peak appeared at 2y ¼30.521, which might be considered as B2O3 [37]. A strong peak in Fig. 1d(1–2) appears at 2y ¼36.551, which is the characteristic peak of Ga2O3 [38,39]. As the amount of doping ions increases, new peaks become strong as depicted above. Especially, for Er3þ :Yb0.3Y2.7 B1.25Ga1.25Al2.5N0.01F0.01O11.99, its peaks have become high and thin after the ions were doped. In addition, the average crystallite sizes of Er3 þ :YbnY3 n BaGabAl5 a bNxFyO12 x y were roughly estimated by calculation from the width of the XRD peaks using the Scherrer equation [40]: D ¼ K l=bcos y where D is average crystallite size, K represents a constant (0.89), l is the XRD wavelength (0.154 nm), b is the corrected half width of the strongest diffraction peak and y is the diffraction angle. It is apparent that with the increase of temperature the diffraction peaks are appreciably broadened. On the basis of the formula, the particle granularities become thin (about 50 nm). However, when the temperature is 1100 1C, the nano-particle size becomes larger (above 62 nm). In the same way, the average sizes of grainy balls encased on the surface of up-conversion luminescence agent were determined to be approximately 50 nm according to Scherrer formula.
Fig. 1. XRD patterns of Er3 þ :Y3Al5O12 with (a) different doping elements (Yb, B, Ga, N and F) ((a-1) Er3 þ :Yb0.3Y2.7Al5O12; (a-2) Er3 þ :Y3B2.5Al2.5O12; (a-3) Er3 þ :Y3Ga2.5Al2.5O12; (a-4) Er3 þ :Y3Al5N0.01O11.99; (a-5) Er3 þ :Y3Al5F0.01O11.99; (a-6) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98); (b) different Yb molar ratio ((b-1) Er3 þ :Yb0.4Y2.6Al5O12 (n¼ 0.4); (b-2) Er3 þ :Yb0.3Y2.7Al5O12 (n¼ 0.3); (b-3) Er3 þ :Yb0.2Y2.8Al5O12 (n ¼0.2); (b-4) Er3 þ :Yb0.1Y2.9Al5O12 (n¼ 0.1); (b-5) Er3 þ :Yb0.0Y3.0Al5O12 (n¼ 0.0)); (c) different B molar ratio ((c-1) Er3 þ :Y3B2.50Al2.50O12 (a¼ 2.50); (c-2) Er3 þ :Y3B1.25Al3.75O12 (a¼1.25); (c-3) Er3 þ :Y3B0.00Al5.00O12 (a¼ 0.00)); (d) different Ga molar ratio ((d-1) Er3 þ :Y3Ga2.50Al2.50O12 (b¼ 2.50); (d-2) Er3 þ :Y3Ga1.25Al3.75O12 (b ¼1.25); (d-3) Er3 þ :Y3Ga0.00Al5.00O12 (b ¼ 0.00)); (e) different N molar ratio ((e-1) Er3 þ :Y3Al5N0.01O11.99 (x¼ 0.01); (e-2) Er3 þ :Y3Al5N0.005O11.995 (x ¼0.005); (e-3) Er3 þ :Y3Al5N0.00O12.00 (x¼ 0.00)); (f) different N molar ratio (f(-1) Er3 þ :Y3Al5F0.01O11.99 (y¼0.01); (f-2) Er3 þ :Y3Al5F0.005O11.995 (y¼0.005); (f-3) Er3 þ :Y3Al5F0.00O12.00 (y ¼0.00)). (Heat-treated at 1100 1C for 120 min).
L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
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Fig. 2. SEM images of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 1100 1C for 120 min).
SEM morphologies of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y powders heat-treated at 1100 1C for 120 min are shown in Fig. 2. It can be seen clearly that there are a large number of elliptic species with average size about 60 nm, which is similar to the result calculated by Scherrer formula. In comparison, the sizes of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y particles are larger than that of Er3 þ :Y3Al5O12 as shown in SEM images of Fig. 2a. It suggests that the crystal lattice has been enlarged by doping ions with larger diameter. For Er3 þ :Yb0.3Y2.7Al5O12, many round particles can be found in Fig. 2b. Fig. 2c shows rod like nanoparticles with average size of 60–80 nm. Images of Er3 þ :Y3Al5N0.01O11.99 and Er3 þ :Y3Al5F0.01O11.99 particles are depicted in Fig. 2e and f, in which 50 nm homogeneous round particles can be seen. Fig. 2g shows that the diameter of larger grey white particles is about 60 nm, of which slight agglomeration phenomenon was found. It can be also observed that the shapes of them appeared in figures are some what different, such as the surface structure, which may be due to the different structures of modified up-conversion luminescence agents. XPS pattern of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 is shown in Fig. 3, in which the amount and type of doping atoms can be detected. Judging from the full and fine spectrum of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 sample, in addition to three kinds of Y, Al and O elements, apparently, there exists a small amount of Er, Yb, B, Ga, N and F. It can be known that these ions have been doped into the crystal lattice of Y3Al5O12. The element C comes from carbon pollution or the carbon precursor body incompletely removed with XPS test. On the basis of XPS, the molar ratio of Yb, B and Ga is 0.8893%, 0.6302% and 0.5939%, respectively. They are slightly less than theoretical measurement. It would suggest that there is relatively low Yb, B and Ga doped amount near the surface. Still, the molar fraction of N and F is 3.51% and 3.36%, respectively, which is slightly more than perspective doped amount. Thus, N and F are indeed doped into the lattice little of Er3 þ :Y3Al5O12 in the form of ionic morphology. 3.2. XRD and SEM of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2 The crystal phases of Er3 þ :Y3Al5O12/TiO2, Er3 þ :Yb0.3Y2.7Al5 O12/TiO2, Er3 þ :Y3B2.5Al2.5O12/TiO2, Er3 þ :Y3Ga2.5Al2.5O12/TiO2, Er3 þ :Y3Al5N0.01O11.99/TiO2, Er3 þ :Y3Al5F0.01O11.99/TiO2 and
Fig. 3. XPS images of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 1100 1C for 120 min).
Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2 were also analyzed by X-ray powder diffractometer in the range of 2y from 101 to 701 shown in Fig. 4. Since the mass ratio of up-conversion luminescence agent is 30% in prepared photocatalyst, the main structure of Y3Al5O12 still can be seen clearly. In comparison with the basic crystal structure of Y3Al5O12, the slight change shows that a small quantity of Er, Yb, B, Ga, N and F ions enter the primary conformation. In addition, new peaks centered at 2y ¼25.341 (1 0 1), 37.941 (0 0 4), 48.241 (2 0 0), 54.021 (1 0 5), 55.161 (2 1 1) and 62.761 (2 0 4) can be observed [41], respectively, which are the characteristic diffraction peaks of anatase phase TiO2 that is the intermediate product with high activity. It could be seen that the characteristic peaks of up-conversion luminescence agent hardly shift, which displays that the crystal change of TiO2 and Er3 þ :Y3Al5O12 are not occurred in the presence of coating of TiO2. And that, no other polymorph was found from the XRD patterns. According to the curve shown in Fig. 4, the peaks of TiO2 and Y3Al5O12 are so high that they have an influence on the performance of up-conversion luminescence agents and the existence of TiO2 makes an impact on the result of the study.
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Fig. 4. XRD patterns of Er3 þ :Y3Al5O12/TiO2 with (a) different doping elements (Yb, B, Ga, N and F) ((a-1) Er3 þ :Yb0.3Y2.7Al5O12/TiO2; (a-2) Er3 þ :Y3B2.5Al2.5O12/TiO2; (a-3)Er3 þ :Y3Ga2.5Al2.5O12/TiO2; (a-4) Er3 þ :Y3Al5N0.01O11.99/TiO2; (a-5) Er3 þ :Y3Al5F0.01O11.99/TiO2; (a-6) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2); (b) different Yb molar ratio ((b-1) Er3 þ :Yb0.3Y2.7Al5O12/TiO2 (n ¼0.3); (b-2) Er3 þ :Yb0.1Y2.9Al5O12/TiO2 (n¼ 0.1); (b-3) Er3 þ :Yb0.0Y3.0Al5O12/TiO2 (n¼0.0)); (c) different B molar ratio ((c-1) Er3 þ :Y3B2.50Al2.50O12/TiO2 (a¼ 2.50); (c-2) Er3 þ :Y3B1.25Al3.75O12/TiO2 (a ¼1.25); (c-3) Er3 þ :Y3B0.00Al5.00O12/TiO2 (a¼ 0.00)); (d) different Ga molar ratio ((d-1) Er3 þ :Y3Ga2.50Al2.50O12/TiO2 (b ¼2.50); (d-2) Er3 þ :Y3Ga1.25Al3.75O12/TiO2 (b ¼1.25); (d-3) Er3 þ :Y3Ga0.00Al5.00O12/TiO2 (b¼ 0.00)); (e) different N molar ratio ((e-1) Er3 þ :Y3Al5N0.01O11.99/TiO2 (x¼ 0.01); (e-2) Er3 þ :Y3Al5N0.005O11.995/TiO2 (x¼ 0.005); (e-3) Er3 þ :Y3Al5N0.00O12.00/TiO2 (x ¼0.00)); (f) different N molar ratio ((f-1) Er3 þ :Y3Al5F0.01O11.99/TiO2 (y ¼0.01); (f-2) Er3 þ :Y3Al5F0.005O11.995/TiO2 (y¼ 0.005); (f-3) Er3 þ :Y3Al5F0.00O12.00/TiO2 (y ¼0.00)). (Heat-treated at 500 1C for 60 min).
The morphologies of TiO2 coating up-conversion luminescence agents, Er3 þ :Y3Al5O12/TiO2, Er3 þ :Yb0.3Y2.7Al5O12/TiO2, Er3 þ :Y3B2.5 Al2.5O12/TiO2, Er3þ :Y3Ga2.5Al2.5O12/TiO2, Er3 þ :Y3Al5N0.01O11.99/TiO2, Er3þ :Y3Al5F0.01O11.99/TiO2 and Er3þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01 O11.98, were characterized by scanning electron microscopy (SEM). In Fig. 5 many grayer spherical particles can be found clearly, which can confirm the rough elliptical form of photocatalyst particles with the average size of 2.0–2.5 mm. In comparison with the SEM shown in Fig. 2, the average size of TiO2 folium is much larger than that of upconversion luminescence agents. It proved that a TiO2 composite particle, in fact, coats many up-conversion luminescence agents particles. Hence, the visible light may sufficiently penetrate through TiO2 folium and excite the inner Er3þ :YbnY3 nBaGabAl5 a b NxFyO12 x y particles, which result in the emission of ultraviolet light. 3.3. Influence of Yb doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 The UV–vis spectra of Er3 þ :Yb0.3Y2.7Al5O12 in the wavelength region of 200–800 nm is detected and the data are shown in Table 1(b). It can be found that in absorption spectra the Er3 þ :Yb0.3Y2.7Al5O12 gives three narrow and strong absorption bands with a maximum at 488 nm, 652 nm and 899 nm, with the corresponding absorbance of 0.052, 0.024 and 0.031, respectively. Although the peak centered at 652 nm is weaker than other two, the absorbance becomes much stronger compared with that of Er3 þ :Y3Al5O12 shown in Table 1(a). The data of up-conversion fluorescence spectrum of Er3 þ : Yb0.3Y2.7Al5O12 in the wavelength of 200–450 nm excited by 488 nm are shown in Table 2-1(b). In principle, the wavelength of the strong emission peaks should be less than 387 nm that can effectively excite TiO2 as photocatalyst. For Er3 þ :Yb0.3Y2.7Al5O12, a peak centered at 317 nm is corresponding to the transition of 2 P3/2-4I15/2 [21,42] with fluorescence intensity of 3.63 104 mau
and full width at half maximum (FWHM) of 10 nm. Apparently, the fluorescence spectrum of Er3 þ :Yb0.3Y2.7Al5O12 gives wider and stronger emission peaks than those of Er3 þ :Y3Al5O12 shown in Table 2-1(a). It suggests that the performance of modified upconversion luminescence agent is better than before. The emission peak at 403 nm is associated with transitions of 2P3/ 2 2- I13/2 [21,42,43] and another peak at 429 nm attributes to the transition of 2G9/2-4I15/2 [21,42] whose FWHM are 3.0 nm and 1.0 nm wider and intensity are 0.20 105 mau and 0.32 105 mau, respectively. Obviously, they are stronger than data shown in Table 2-1(a). In other word, because of Yb doping the peaks all become stronger and wider than those of Er3 þ :Y3Al5O12. Table 2-2(b) shows that the intensities of the emission peaks at 246 nm corresponding to 3I4-3P5/2 [44] and 497 nm related to 4 S3/2-4I15/2 [44], with 1.42 104 mau and 3.28 104 mau, respectively, are not so strong compared with that of Er3 þ :Y3Al5O12 shown in Table 2-2(a). However, the peak at 588 nm which belongs to 2G9/2-4I13/2 [44] is strong enough. Furthermore, the FWHM of three peaks shown in Table 2-3(b) are all wider than those shown in Table 2-3(a). The emission peak at 491 nm which is assigned to 4F7/2-4I15/2 [10,46] is much stronger than corresponding that of Er3 þ :Y3Al5O12. And that, the peaks at 268 nm and 426 nm corresponding to 4G7/2-4I15/2 and 2G9/2-4I15/2 [10,45], respectively, are similar to those displayed in Table 2-3(a). The emission peak at 491 nm which is assigned to 4 F7/2-4I15/2 [10,46] is much strong. In any case, the doped Yb ion as a sensitizer plays a certain role in enlarging the spectrum range and intensity to some extent. 3.4. Influence of B and Ga doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 The data of absorption and emission spectra of Er3 þ :Y3B2.5 Al2.5O12 and Er3 þ :Y3Ga2.5Al2.5O12 shown in Table 1(c) and (d) and Table 2(c) and (d) suggest that spectra of modified up-conversion
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Fig. 5. SEM images of (a) Er3 þ :Y3Al5O12/TiO2; (b) Er3 þ :Yb0.3Y2.7Al5O12/TiO2; (c) Er3 þ :Y3B2.5Al2.5O12/TiO2; (d) Er3 þ :Y3Ga2.5Al2.5O12/TiO2; (e) Er3 þ :Y3Al5N0.01O11.99/TiO2; (f) Er3 þ :Y3Al5F0.01O11.99/TiO2; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2. (Heat-treated at 500 1C for 60 min).
Table 1 Characteristic absorption spectra of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 500 1C for 60 min). Sample
First absorption peak
Second absorption peak
(No:)
Peak position (nm)
Absorbance (au)
Peak position (nm)
Absorbance (au)
Peak position (nm)
Absorbance (au)
a b c d e f g
488 488 488 488 488 488 488
0.009 0.052 0.029 0.023 0.029 0.040 0.058
653 652 648 648 650 650 649
0.014 0.024 0.051 0.014 0.019 0.032 0.042
896 899 898 893 893 899 898
0.002 0.031 0.053 0.012 0.021 0.028 0.042
luminescence agents are improved compared with that of Er3 þ :Y3Al5O12 shown in Table 1(a) and Table 2(a). It indicates that doping B and Ga makes an effect on enhancing spectrum intensity. The absorption spectrum of Er3 þ :Y3B2.5Al2.5O12 shown in Table 1(c) displays an obvious increase in peak width. The same phenomenon can be seen in Table 1(d), and peaks centered at 488 nm, 648 nm and 893 nm all become stronger than that Er3 þ :Y3Al5O12 of in Table 1(a). It is desirable that the emission spectra within ultraviolet range are strong enough to stimulate TiO2, which could increase the utilization rate of solar light. In Table 2-1(c), it can be seen that the peaks centered at 403 nm and 429 nm do not change compared with those in Table 2-1(a), but the peak centered at 318 nm becomes stronger than that in Table 2-1(a). In Table 2-2(c), the emission peaks at 492 nm and 582 nm become strong and FWHM of peaks at 246 nm and 582 nm become wide obviously. It indicates that doped B enhances the peak intensity and width to some extent. In Table 2-3(c), the peak at 260 nm which shifts a little is wider than that at the same wavelength in Table 2-3(a). The characterized peaks all become wide and that the peaks at 421 nm and 495 nm become strong enough. As shown in Table 2-1(d), the peak centered at 429 nm is much stronger than that in Table 2-1(a). In Table 2-2(d), all peak widths become wide by 2–4 nm, whereas only the peak at 582 nm is not so strong. In Table 2-3(d), all peak widths broaden much, but the peak intensities hardly change.
Third absorption peak
3.5. Influence of N and F doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 As seen in Table 1(e), all absorption peaks of Er3 þ :Y3Al5N0.01 O11.99 become strong. Especially, the absorbance at 488 nm and 893 nm are intensified by a large margin, with amplification of 0.020 and 0.019, respectively. The absorbance of Er3 þ :Y3Al5F0.01 O11.99 in Table 1(f) increase to 0.031, 0.018 and 0.026, respectively, but the peak positions do not express obvious changes. It indicates that doping of N and F makes more visible light convert into ultraviolet light. In Table 2-1(e) and (f), the emission peaks at l ¼319 nm, 404 nm and 429 nm are somewhat similar to the data in Table 2-1(a), but their FWHM becomes wider by 3–6 nm. Especially, the first emission peak becomes very wide and the wavelength range is from l ¼317 nm to l ¼ 319 nm. Table 2-1(e) shows the similar peak position to Table 2-1(a), but the ultraviolet light emission peak in the wavelength region of 340–400 nm is wider than that of Er3 þ :Y3Al5O12. In Table 2–2(e), the intensity of the ultraviolet light emissions at l ¼246 nm is not so strong but the FWHM was enlarged by 5 nm. Nevertheless, both the peak width and intensity of the other two peaks are enhanced largely. In Table 2-3(e), the FWHM are all enlarged by 3–5 nm, whereas only the peak intensity at 426 nm becomes very strong. As shown in Table 2-1(f), the peak intensity becomes much strong compared with that of Er3 þ :Y3Al5O12 and the FWHM also becomes
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Table 2 Characteristic emission spectra of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 500 1C for 60 min). Sample
2
P3/2-4I15/2
(No:)
Peak position (nm)
P3/2-2I13/2
Half band width (nm)
Intensity Peak position (104 ma.u) (nm)
(1) Under 488 nm excitation A 317 9 B 317 10 C 318 10 D 319 13 E 318 15 F 319 15 G 312 10.5 3 Sample I4-3P5/2 (No:) Peak position Half band width (nm) (nm)
3.25 3.63 3.27 3.25 3.22 3.77 3.02
404 403 403 404 404 403 404
Intensity (104ma.u)
Peak position (nm)
(2) Under 653 nm excitation A 246 6 B 246 7 C 246 13 D 235 10 E 246 11 F 245 12 G 220 10 4 Sample G7/2-4I15/2 (No:) Peak position Half band width (nm) (nm)
1.42 1.42 1.06 2.13 1.38 0.52 0.44
496 497 492 496 497 494 497
Intensity (102ma.u)
Peak position (nm)
(3) Under 900 nm excitation A 266 5 B 268 6 C 260 7 D 255 7 E 266 10 F 262 10 G 269 9
2.91 0.67 1.24 0.92 1.85 1.08 2.55
426 426 421 426 426 420 425
G9/2-4I15/2
2
2
Half band width Intensity (nm) (105ma.u)
Peak position (nm)
Half band width (nm)
Intensity (105ma.u)
8 11 14 12 12 12 14 4 S3/2-4I15/2 Half band width (nm)
1.55 1.75 1.51 1.56 1.50 1.70 1.39
432 429 429 429 429 429 429
2.31 2.63 2.28 2.41 2.31 2.59 2.11
Intensity (104ma.u)
Peak position (nm)
9 10 9 10 12 12 14 2 G9/2-4I13/2 Half band width (nm)
3.28 3.28 3.03 3.31 3.93 3.87 0.67
580 588 582 582 588 584 587
4 6 12 13 9 9 11
Intensity (104ma.u)
Peak position (nm)
4 F7/2-4I15/2 Half band width Intensity (nm) (102ma.u)
3.28 3.28 3.03 1.31 3.93 3.87 0.67
495 491 495 502 493 493 495
5 6 7 8 11 8 9
5 7 5 8 10 5 11 2 G9/2-4I15/2 Half band width (nm)
6 7 10 7 10 11 12
Intensity (104ma.u)
3.35 4.64 4.26 2.04 4.83 5.34 1.10
17.10 37.00 42.31 3.76 5.86 3.64 17.93
wide in a large scale. In Table 2-2(f), both of the emission peak intensity and FWHM are enhanced more or less, which indicates the doping F ion makes the emission peaks become wide and strong. In Table 2-3(f), FWHM all become wide and only peak at 420 nm become strong, which suggests that the doping N or F ion might not enhance both the peak intensity and width at the same time. 3.6. Influence of Yb, B, Ga, N and F co-doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 In Table 1(g), the absorption peaks at 488 nm, 649 nm and 898 nm are all very strong. In fact, the absorbance becomes quite intense compared to that (Table 1(a)) of Er3 þ :Y3Al5O12. The appealing result is the anti-stokes emission under 400 nm wavelength excitation, which displays an enhancement for up-conversion effect of Er3 þ :Y3Al5O12. It suggests that the modified upconversion luminescence agents make more visible light converted to ultraviolet light. At last, as a special case the fluorescence emission spectrum of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 under excitation of 488 nm wavelength light was given in Fig. 6. For comparison, the fluorescence emission spectrum of Er3 þ :Y3Al5O12 was also provided in Fig. 6. Particularly, the emission spectra in the range of 200–450 nm which is matching with the energy band gap (Ebg ¼3.2 eV) of TiO2 was researched. As depicted in Fig. 6, all emission peaks of modified up-conversion luminescence agent (Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98) become stronger and wider than ones of Er3 þ :Y3Al5O12, which indicates the effects
Fig. 6. Fluorescence emission spectra (lex ¼488 nm) of Er3 þ :Y3Al5O12 (a) and Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 (g).
of co-doping ions (Yb, B, Ga, N and F) once again. In detail, as shown in Table 2-1(g), the peak intensity becomes slightly strong but the peak width is much enlarged. The emission peaks at 312 nm, 404 nm and 429 nm were broadened by 1.5 nm, 6.0 nm and 5.0 nm, respectively. In Table 2-2(g), the same variation trend can be seen. It suggests that more emission light was converted. In Table 2-3(g), the emission peaks become a little wide but the peak intensity only at 495 nm becomes strong. In sum, the intensity and width of emission spectra are both improved in a
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photocatalysts reveal high photocatalytic activity in the degradation of organic dyes.
4. Conclusions
Fig. 7. Degradation of different dyes (with up-conversion luminescence agent: TiO2 ¼3: 10 (heat-treated at 500 1C for 60 min) amount, 24–28 1C temperature and 120 min solar light irradiation). (a) Er3 þ :Y3Al5O12/TiO2; (b) Er3 þ :Yb0.3Y2.7 Al5O12/TiO2; (c) Er3 þ :Y3B1.25Al3.75O12/TiO2; (d) Er3 þ :Y3Ga1.25Al3.75O12/TiO2; (e) Er3 þ :Y3Al5N0.005O11.995/TiO2; (f) Er3 þ :Y3Al5F0.005O11.995/TiO2; (g) Er3 þ :Yb0.3 Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2.
large scale. The doping ions serve as strengthening and widening spectra for up-conversion luminescence agents. 3.7. Photocatalytic activity of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y in degradation of organic dyes under solar light irradiation The degradation ratio was detected by UV–vis spectrometer because the absorbance of ordinary dye solution with low concentration abides by Lambert–Beer Law. The degradation ratio of different organic dyes under solar light irradiation (21–25 1C temperature, 8.00–10.00 a.m. and 2.00–4.00 p.m. every day in June, E1231270 and N711500 , Shenyang City, China) is shown in Fig. 7. After 60 min, with fragmentation of the azo bonds and naphthyl rings attacking, obvious degradation rate is obtained. Anyway, these results suggest that these dye molecules were already decomposed. In addition, under the same solar light irradiation the degradation ratio is much higher in the presence of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y/TiO2 compared to that in the presence of Er3 þ :Y3Al5O12/TiO2. Apparently, that is because the doping of Yb, B, Ga, N and F enhances the visible light absorption capability and ultraviolet light emission intensity of Er3 þ : Y3Al5O12, which further improves the photocatalytic activity of TiO2. These doping atoms demonstrate a good synergistic effect during up-conversion luminescence process, which is in accordance with the deduction ratios of various organic dyes in Fig. 7. Of course, due to the different molecule structures and chemical compositions, these used organic dyes show different degradation ratios. Methylene Blue was easy to degrade for the high photosensitivity. On the other hand, the degradation of Rhodamine B was lower than other dyes. In any way, all selected organic dyes could be degraded to some extent. It indicates the prepared TiO2 photocatalyst coating up-conversion luminescence agents should be broad-spectrum in photocatalytic degradation of various organic dyes. On the whole, for all used organic dyes, the degradation ratio in the presence of Er3 þ :Yb0.3Y2.7B1.25Ga1.25 Al2.5N0.01F0.01O11.98 is highest. The enhancement of the photocatalytic activity is due to the performance of modified up-conversion luminescence agents with other ions. The participation of other doped ions made the absorption and emission spectra become wider more or less, which leads to more transformation of visible light in solar spectra to ultraviolet light. Thus, the modified
The study aims at investigating the effect of some doping elements into Er3 þ :Y3Al5O12 on the luminescence characteristics and the photocatalytic performance of the corresponding Er3 þ :Y3Al5O12/TiO2 composites. In summary, we have developed an important synthesis of up-converted luminescence agents (Er3þ : Y3Al5O12, Er3 þ :YbnY3 nAl5O12, Er3 þ :Y3BaAl5 aO12, Er3 þ :Y3Gab Al5 bO12, Er3 þ :Y3Al5NxO12 x, Er3 þ :Y3Al5FyO12 y and Er3þ :YbnY3 n BaGabAl5 a bNxFyO12 x y) and their corresponding photocatalysts with TiO2 coating (Er3 þ :Y3Al5O12/TiO2, Er3 þ :YbnY3 nAl5O12/TiO2, Er3 þ :Y3BaAl5 aO12/TiO2, Er3 þ :Y3GabAl5 bO12/TiO2, Er3þ :Y3Al5Nx O12 x/TiO2, Er3þ :Y3Al5FyO12 y/TiO2 and Er3 þ :YbnY3 nBaGab Al5 a bNxFyO12 x y/TiO2). These prepared up-converted luminescence agents can present wide excitation wavelength and then produce strong emission peaks via the effective up-conversion process. That is, ultraviolet, violet and blue up-conversion luminescence emissions of Er3 þ :YbnY3 nGaaBbAl5 a bNxFyO12 x y could be observed under 488 nm, 654 nm and 900 nm light excitation. Judging from the result, the process is particularly effective when the Er3 þ :Y3Al5O12 is doped with Yb, B, Ga, N and F together. It should be noted that Yb as a sensitizer in the host lattice makes a significant contribution to the up-conversion emission and absorption spectra. Up-conversion luminescence agents doped with N and F exhibit somewhat spanning of deep UV regions light. And B and Ga make the absorption and emission peaks become strong in the results. At last, the prepared TiO2 coated composites are used to detect the photocatalytic degradation ratio of some organic dyes. It indicates that the photocatalytic activity of TiO2 can be enhanced obviously by modified up-conversion luminescence agents in dyes degradation. Of which, the Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2 displays the most effective photocatalytic activity in dyes degradation under solar light irradiation.
Acknowledgments The authors greatly acknowledge the National Natural Science Foundation of China, Liaoning Province Natural Science Foundation of Education Department, Liaoning Province Natural Science Foundation of Science and Technology Department and Liaoning university ‘‘211’’ project for financial support. The authors also thank our colleagues and other students for their participating in this work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
C.M. So, M.Y. Cheng, J.C. Yu, P.K. Wong, Chemosphere 46 (2002) 905. C. Debabrata, M. Anima, J. Photochem. Photobiol., A 153 (2002) 199. C. Karunakaran, R. Dhanalakshmi, Sol. Energy Mater. Sol. Cells 92 (2008) 588. J. Wang, Y.H. Lv, L.Q. Zhang, B. Liu, R.Z. Jiang, G.X. Han, R. Xu, X.D. Zhang, Ultrason. Sonochem. 17 (2010) 642. X.W. Zhang, L.C. Lei, J.L. Zhang, Q.X. Chen, J.G. Bao, B. Fang, Sep. Purif. Technol. 67 (2009) 50–57. X.F. You, F. Chen, J.L. Zhang, M. Anpo, Catal. Lett. 102 (2005) 247. N. Barka, S. Qourzal, A. Assabbane, A. Nounah, Y. Aˆıtichou, J. Photochem. Photobiol., A: Chem 195 (2008) 346. R. Comparelli, E. Fanizza, M.L. Curri, P.D. Cozzolia, G. Mascoloc, A. Agostiano, Appl. Catal., B: Environ 60 (2005) 1. J. Wang, G. Zhao, Z.H. Zhang, X.D. Zhang, G. Zhang, T. Ma, Y.F. Jiang, P. Zhang, Y. Li, Dyes Pigm. 75 (2007) 335. R. Francini, S. Pietrantoni, M. Zambelli, A. Speghini, M. Bettinelli, J. Alloys Compd. 380 (2004) 34. W.J. Tobler, W. Durisch, Appl. Energy 85 (2008) 483. H.M.H. Fadlalla, C.C. Tang, J. Cryst. Growth 311 (2009) 3737. D. Jaque, J. Capmany, F. Molero, Z.D. Luo, J.G. Sole, Opt. Mater. 10 (1998) 211.
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L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
[14] Z.G. Hu, M. Yoshimura, Y. Mori, T. Sasaki, K. Kato, Opt. Mater. 23 (2003) 353. [15] J. Wang, J. Li, Y.P. Xie, C.W. Li, G.X. Han, L.Q. Zhang, R. Xu, X.D. Zhang, J. Environ. Manage. 91 (2010) 677. [16] V. Mahalingam, F. Vetrone, R. Naccache, A. Speghini, J.A. Capobianco, Adv. Mater. 21 (2009) 4025. [17] M. Szachowicz, S. Tascu, M.F. Joubert, P. Moretti, M. Nikl, Opt. Mater. 28 (2007) 162. [18] J. Wang, F.Y. Wen, Z.H. Zhang, X.D. Zhang, Z.J. Pan, P. Zhang, P.L. Kang, J. Tong, L. Wang, L. Xu, J. Photochem. Photobiol., A 180 (2007) 189. [19] R. Xu, J. Li, J. Wang, X.F. Wang, B. Liu, B.X. Wang, X.Y. Luan, X.D. Zhang, Sol. Energy Mater. Sol. Cells 94 (2010) 1157. [20] J. Wang, R.H. Li, Z.H. Zhang, W. Sun, R. Xu, Y.P. Xie, Z.Q. Xing, X.D. Zhang, Appl. Catal., A 334 (2008) 227. [21] N.N. Zu, H.G. Yang, Z.W. Dai, Physica B 403 (2008) 174. ¨ zen, O. Forte, B. Di Bartolo, Opt. Mater. 27 (2005) 1664. [22] G. O [23] D. Sangla, N. Aubry, A. Nehari, A. Brenier, O. Tillement, K. Lebbou, F. Balembois, P. Georges, D. Perrodin., J. Didierjean, J.M. Fourmigue, J. Cryst. Growth 312 (2009) 125. [24] L.A. Diaz-Torrdes, E. De la Rosa, P. Salas, H. Desirena, Opt. Mater. 27 (2005) 1305. [25] X.D. Wang, X.D. Xu, Z.W. Zhao, B.X. Jiang, J. Xu, G.J. Zhao, P.Z. Deng, G. Bourdet, J.C. Chanteloup, Opt. Mater. 29 (2007) 1662. ¨ ¨ [26] J.F. Suyver, J. Grimm, K.W. Kramer, H.U. Gudel, J. Lumin. 114 (2005) 53. [27] L.F. Liang, X.M. Zhang, H.L. Hu, L. Feng, M.M. Wu, Q. Su, Mater. Lett. 59 (2005) 2186. [28] G. Dominiak-Dzik, P. Solarz, W. Ryba-Romanowski, E. Beregi, L. Kova´cs, J. Alloys Compd. 359 (2003) 51. [29] P.Y. Jia, J. Lin, X.M. Han, M. Yu, Thin Solid Films 483 (2005) 122.
[30] X.P. Chen, Q.Y. Zhang, C.H. Yang, D.D. Chen, C. Zhao, Spectrochim. Acta, Part A 74 (2009) 441. [31] Z.Q. Li, Y. Zhang, S. Jiang, Adv. Mater. 24 (2008) 4765. [32] M. Dulick, G.E. Faulkner, N.J. Cockroft, D.C. Nguyen, J. Lumin. 48–49 (1991) 517. [33] S. Nicolas, E. Descroix, M.F. Joubert, Y. Guyot, M. Laroche, R. Moncorge´, R. Yu Abdulsabirov, A.K. Naumov, V.V. Semashkod, A.M. Tkachuke, M. Malinowskif, Opt. Mater. 22 (2003) 139. [34] D.V. Arkhipov, T.I. Khristov, N.V. Popovich, S.S. Galaktionov, N.P. Soshchin, Inorg. Mater. 32 (1996) 459. [35] F.E. Ghodsi, F.Z. Tepehan, G.G. Tepehan, Sol. Energy Mater. Sol. Cells 92 (2008) 234. [36] J. Wang, Y.P. Xie, Z.H. Zhang, J. Li, X. Chen, L.Q. Zhang, R. Xu, X.D. Zhang, Sol. Energy Mater. Sol. Cells 93 (2009) 355. [37] Z.B. Hu., H.J. Li., Q.G. Fu., H. Xue, G.L. Sun, New Carbon Mater. 22 (2007) 131. [38] H.F. Jiang, Y.Q. Chen, Q.T. Zhou, Y. Su, H.H. Xiao, L.A. Zhu, H.F. Jiang, Mater. Chem. Phys. 103 (2007) 14. [39] B.C. Kim, K.T. Sun, K.S. Park, K.J. Im, T. Noh, M.Y. Sung, S. Kim, S. Nahm, Y.N. Choi, S.S. Park, Appl. Phys. Lett. 80 (2002) 479. [40] P.F.S. Pereira, J.M.A. Caiut, S.J.L. Ribeiro, Y. Messaddeq, K.J. Ciuffia, L.A. Rocha, E.F. Molina, E.J. Nassar, Ceram. Int. 126 (2007) 378. [41] J.Q. Gao, R.Z. Jiang, J. Wang, B.X. Wang, K. Li, P.L. Kang, Y. Li, X.D. Zhang, Chem. Eng. J. 168 (2011) 1041. [42] H.L. Xu, Z.K. Jiang, Chem. Phys. 287 (2003) 155. [43] S. Du, J.X. Xu, X.R. Dong, J. Zhang, Z.L. Fu, Z.W. Dai, J. Lumin. 130 (2010) 872. [44] H.G. Yang, Z.W. Dai, Z.W. Sun, J. Lumin. 124 (2007) 207. [45] G.Y. Chen, Y. Liu, Z.G. Zhang, B. Aghahadi, G. Somesfalean, Q. Sun, F.P. Wang, Chem. Phys. Lett. 448 (2007) 127.
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Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Effect of different doped elements on visible light absorption and ultraviolet light emission on Er3 þ :Y3Al5O12 Linuan Yin a, Ying Li a, Jun Wang a,n, Yu Zhai a, Yumei Kong b, Jingqun Gao a, Guangxi Han a, Ping Fan a,n a b
College of Chemistry, Liaoning University, Shenyang 110036, PR China College of Pharmacy, Liaoning University, Shenyang 110036, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 December 2011 Received in revised form 3 June 2012 Accepted 15 June 2012 Available online 26 June 2012
In this progress report, seven kinds of novel carefully designed and fabricated up-conversion luminescence agents, Er3 þ :Y3Al5O12, Er3 þ :YbnY3 nAl5O12, Er3 þ :Y3BaAl5 aO12, Er3 þ :Y3GabAl5 bO12, Er3 þ :Y3Al5NxO12 x, Er3 þ :Y3Al5FyO12 y and Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y, are successfully synthesized using sol–gel methods. After that, their corresponding photocatalysts, Er3 þ :Y3Al5O12/TiO2, Er3 þ :YbnY3 nAl5O12/TiO2, Er3 þ :Y3BaAl5 aO12/TiO2, Er3 þ :Y3GabAl5 bO12/TiO2, Er3 þ :Y3Al5NxO12 x/TiO2, Er3 þ :Y3Al5FyO12 y/TiO2 and Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2, are also prepared by sol–gel coating process. The obtained up-conversion luminescence agents and photocatalysts were characterized by using XRD, XPS, SEM, UV–vis and fluorescence spectrophotometer. Synchronously, several kinds of organic dyes are used to test their photocatalytic degradation using prepared photocatalysts. It indicates that the up-conversion luminescence ability of Er3 þ :Y3Al5O12 can be improved obviously through doping of some elements. And then, the photocatalytic activity of TiO2 is markedly enhanced by modified up-conversion luminescence agents which can transform much visible light into ultraviolet light. & 2012 Elsevier B.V. All rights reserved.
Keywords: Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y Up-conversion luminescence Effect of doped elements Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/ TiO2 Photocatalytic activity
1. Introduction In recent years, exploring new energy and material is attracting much attention for the contamination of environment, particularly, the use of solar energy appeals to many researchers [1–3]. TiO2 as a n-type semiconductor material plays an important role in removal of organic pollutants and use of solar power generation [4]. Its widely application is due to biological and chemical long-term stability, strong oxidizing power, low cost, against photocorrosion and chemical corrosion [5–8]. However, a general problem in use of TiO2 systems is the limited absorption spectrum. TiO2 absorbs strongly only during ultraviolet light below wavelength 387 nm [9], which limits the utilization of visible light sufficiently and leads to lower efficiency and high costs on utilizing TiO2. Er3 þ :Y3Al5O12 is a promising up-conversion luminescence agent precursor and can make visible light translate into ultraviolet light [10–12]. In our previous work, Er3 þ :Y3Al5O12/TiO2 composites had been studied in detail [13,14]. The changes of the corresponding spectra in the Er3 þ :Y3Al5O12 following the absorption of visible light and emission of ultraviolet light illustrate the high up-conversion activity. Hence, the TiO2 composite with
n
Corresponding authors. Tel.: þ 86 24 62207859; fax: þ 86 24 62202053. E-mail address: [email protected] (J. Wang).
0022-2313/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2012.06.017
up-conversion luminescence agent can make use of solar light efficiently. In the communication, for example, it becomes a reality to use ZnO–TiO2 coating Er3 þ :Y3Al5O12 in solar cell and dyes degradation under solar light irradiation [15]. The reason for this application, on the one hand, is largely because of their unique intra 4f transition [16]. On the other hand, it is due to the particular characters of TiO2 and ZnO, which possess superior photoreactivity, nontoxicity and long term stability. When the proportion of Er3 þ is 1.0 at%, the up-conversion efficiency of Er3 þ :Y3Al5O12 is high enough [17,18]. The photocatalytic activity of Fe and Co-doped TiO2 in degradation of organic dyes is obviously enhanced by Er3 þ :YAlO3 [19]. Nevertheless, the ultraviolet light (l o387 nm) generated by the Er3 þ :Y3Al5O12 is not sufficiently absorbed by TiO2. Mainly, Er3 þ :Y3Al5O12 is constrained by its narrow absorption spectra and weak excitation spectra [20]. In order to effectively utilize solar energy for environmental pollution control and solar electrical energy generation, it is urgent to further enhance the up-conversion luminescence efficiency of Er3 þ :Y3Al5O12. Perhaps, the doping of other ions into Er3 þ :Y3Al5O12 can improve the upconversion luminescence. According to the reports, up-conversion intensity can become strong due to Pr doping Er3 þ :Y3Al5O12 [21,22], but the absorption and emission spectra are still narrow. The infrared light is translated into visible light with Yb3 þ doping Er3 þ :Y3Al5O12 [23–25], which can also enhance the up-conversion ability of Er3 þ :Y3Al5O12. The up-conversion luminescence
L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
can take place with B doping Y3Al5O12 [26], including K2Al2B2O7 [27] and YAl3B4O12 [28]. Among them, K2Al2B2O7 makes the visible light translate into ultraviolet light. Jia et al. made a research on Y3GaxAl5 xO12 films doped with rare earth ion [29], which shows good luminescence property. The strong ultraviolet light can also be detected from Yb3 þ /Tm3 þ co-doped LiYF4, BaYF5 and NaYF4 [30–33]. It turned out to be a great improvement for the past work, but the spectrum range is still unsatisfied. Thus, the utilization of solar energy by up-conversion luminescence is limited still. To compensate the disadvantage of up-conversion luminescence agent, in this work, through systematically doping other ions we tried to widen the spectrum range. That is, doping Yb, B, Ga, N and F makes the absorption spectrum range and emission spectrum intensity of Er3 þ :Y3Al5O12 enlarge much. Theoretically, these doping ions can change the crystal field and energy level around the central Er ion in a way. Concretely, the purpose to dope Yb is to sensitize Er3 þ :Y3Al5O12 and enhance the upconversion activity. Further, up-conversion and emission scopes are rationally enlarged through doped ions with defined concentrations. Al is replaced by B and Ga atoms, which have small and big ionic diameter compared with Al, respectively, to enhance the visible light absorption range and ultraviolet light emission intensity. For this reason, as e/r changing great, the intensity of crystal field inside will be transformed. In the same way, N and F are used to replace O in order to enhance the absorption and emission extent, for their different electronegativity and radius from O atom. The improvement of up-conversion ability of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y might be attributed to the presence of Yb, B, Ga, N and F. It supposed that the Er3 þ : YbnY3 nBaGabAl5 a bNxFyO12 x y would become a great promising up-conversion luminescence system. In this paper, we reported that some elements were used to dope into Er3 þ :Y3Al5O12 and then coated by TiO2 film to form novel photocatalysts. That is, several new up-conversion luminescence agents and corresponding photocatalysts with excellent performance are prepared by a simple sol–gel procedure. Structural properties were studied by X-ray powder diffractometer (XRD). Grain sizes have been calculated and estimated based on the XRD patterns and SEM images. The category and amount of doping ions were detected by XPS. Decay curves of absorption and emission spectra have been recorded and analyzed using UV–vis and fluorescence spectrophotometer. And then, the photocatalytic performance of different TiO2 coated composites of Er3 þ :Y3Al5O12 doping with Yb, B, Ga, N and F was studied through the degradation of some organic dyes under solar light irradiation. The results indicate these modified up-conversion luminescence agent have the additional advantage of widening and intensifying up-conversion spectra, thus opening up vast opportunities for solar cell and sewerage treatment. We believe that the enormous improvement of the up-conversion efficiency of these up-conversion luminescence materials opens the door for future applications in the field of solar cell.
2. Experimental
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powders were dissolved in HNO3 (65%, Veking Company, China) with magnetic stirring and heating until transparent. 2.9566 g Al(NO3)3 9H2O (99.99%, Veking Company, China) was dissolved in 30 mL distilled water. At room temperature, the aqueous solution of aluminum nitrate solution was introduced slowly into the rare earth metal ion solutions under vigorous stirring. Then 8.0301 g citric acid (C6H8O7 H2O, 99.99%) was added as chelating agent and assistant solvent, in a molar ratio of citric acid:metalion¼ 3:1. Then the remaining solution was stirred and heated at 50–60 1C until the transparent solution was successfully prepared. In the process of drying, no deposit was formed until all solvent was evaporated and the foamy gel was finally obtained. Afterwards, the gel was heated at 80 1C and ground into fine homogeneous powders. The collected powders were heated at 500 1C for 50 min, and then kept at 1100 1C for 2.0 h. At last, the sintered substance was taken out of the tube furnace and allowed to cool down to the room temperature in atmosphere. Then, the desired white Er3 þ :Yb0.4Y2.6Al5O12 powder was obtained. The synthesis methods of Er3þ :Y3Al5O12, Er3þ :Y3BaAl5 aO12 (a¼1.25–2.50), Er3 þ :Y3GabAl5 bO12 (b¼1.25–2.50), Er3 þ :Y3Al5 NxO12 x (x¼0.005–0.010), Er3þ :Y3Al5FyO12 y (y¼0.005–0.010) and Er3 þ :Yb3 nYnGaaBbAl5 a bNxFyO12 x y (n¼0.0–0.4, a¼b¼1.25– 2.50, x¼y¼0.005–0.010) were similar to above mentioned. In order to prevent the volatilization of H3BO3, ethanediamine (C2H8N2) and HF, they were added after the solution was neutral and transparent. 2.2. Preparation of Er3 þ :YbnY3 nGaaBbAl5 a bNxFyO12 x y/TiO2 Take Er3þ :Yb0.3Y2.7Al5O12/TiO2 for example, Er3 þ :Yb0.3Y2.7Al5O12/ TiO2 composite was prepared through the ultrasonic dispersion and sol–gel method [35]. The molar ratio of Ti(O–Bu)4:ethanol:H2O:acetic acid was controlled at 1:10:2:1 and the final quality ratio of TiO2 and Er3 þ :Yb0.3Y2.7Al5O12 was controlled at 1.0:0.3. At first, through treating a suspension of Er3 þ :Yb0.3Y2.7Al5O12 particle in an ultrasonic bath for 10 min the transparent colloidal solution containing 1.0 wt% Er3 þ :Yb0.3Y2.7Al5O12 was obtained. Second, a homogeneous solution of Ti(O–Bu)4 in ethanol was used as titanium dioxide precursor. The mixed solution of ethanol, acetic acid and deionized water were gradually added into above solution under stirring magnetically. The final pH value of solution was about 3.0. After 10 min stirring, 0.3000 g Er3 þ : Yb0.3Y2.7Al5O12 colloidal solutions were added into the final solution with stirring until to gel. The gel was heated to 120 1C in oven and kept at constant temperature for 120 min. Afterwards, the temperature was controlled at 500 1C for 60 min. Finally, the Er3 þ :Yb0.3Y2.7Al5O12/TiO2 composite particles were obtained. The synthesis method of Er3þ :Y3Al5O12/TiO2, Er3 þ :Y3BaAl5 aO12/ TiO2 (a¼1.25–2.50), Er3þ :Y3GabAl5 bO12/TiO2 (b¼1.25–2.50), Er3 þ : Y3Al5NxO12 x/TiO2 (x¼0.005–0.010), Er3 þ :Y3Al5FyO12 y/TiO2 (y¼ 0.005–0.010) and Er3 þ :Yb3 nYnGaaBbAl5 a bNxFyO12 x y/TiO2 (n¼ 0.0–0.4, a¼b¼1.25–2.50, x¼y¼ 0.005–0.010) were the same as mentioned above. 2.3. Characterization of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y and corresponding Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2 photocatalysts
2.1. Synthesis of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y Er3 þ :YbnY3 nAl5O12 (n ¼0.00–0.40 at 0.10 intervals) doped with Yb3 þ ion were synthesized via sol–gel procedure in the presence of citric acid (C6H8O7 H2O, 99.99%, Veking Company, China) as chelating agent according to the following process [34]. Take Er3 þ :Yb0.4Y2.6Al5O12 for example, 0.0031 g Er2O3 (99.99%, Veking Company, China), 0.1255 g Yb2O3 (99.99%, Veking Company, China) and 0.4650 g Y2O3 (99.99%, Veking Company, China)
For confirming the formation of anatase phase and estimating the proportion of different crystalline phases, the X-ray powder diffraction (XRD) patterns were determined by X-ray powder diffractometer (D-8, Bruker-axs, Germany) using Ni-filtered Cu Ka radiation in the range of 2y from 101 to 701. Scanning electron microscopy (SEM, JEOLJSM-5610LV, Hitachi Corporation, Japan) was used to detect the morphology of particles. Fluorescence spectrophotometer (FLSP920, Edinburgh Instruments, UK) was
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adopted to detect the emission spectra of Er3 þ :YnYb3 nGaaBb Al5 a bNxFyO12 x y. And the UV–vis spectrometer (LAMBDA-17, Perkin–Elmer Company, USA) was applied to judge the excitation wavelength of up-conversion luminescence agents and degradation ratios of dyes in aqueous solutions. 2.4. Investigation of solar photocatalytic activity of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y The evaluation of photocatalytic activity of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y/TiO2 composites heat-treated at 500 1C for 60 min was carried out through the degradation of some organic dyes under given conditions such as 10 mg/L initial concentration, 1000 mg/L photocatalyst addition amount and 100 mL total volume except special demand. The dye suspensions were irradiated by solar light after agitation in dark for 30 min. Then, the suspensions were sampled at specific intervals to determine the changes of dye concentration. The sampled suspensions were centrifuged three times at 4000 rpm for 30 min to obtain the clear solution. The UV–vis spectrometer was used to analyze the degradation ratio of the dye solution.
3. Results and discussion 3.1. XRD, SEM and XPS of Er3 þ :YbnY3 nBaGabAl5 a bNxFiO12 x y The prepared samples were investigated by powder X-ray diffractometer (XRD) over the 2y range between 101 and 701. Fig. 1 intriguingly shows the changes of different Er3 þ :YbnY3 nBaGab Al5 a bNxFyO12 x y powders in XRD patterns. By and large, various doped ions seem to enhance their diffraction peak intensities. The main characteristic peaks are displayed at 2y ¼18.121 (211), 33.361 (400), 42.581 (422), 46.621 (521) and 55.121 (532) in all given Fig. 1, which indicates the presence of elementary Er3þ :Y3Al5O12 composition. Fig. 1a(1–6) shows the peak characters of different up-conversion luminescence agents. It can be seen that doping ions make peaks change a little both in peak intensity and position. Fig. 1b(1–5) shows
that the characteristic diffraction peaks slightly sharpen along with the increase of Yb doping quantity [36], and no change in phase composite, but few changes can be found when n40.30. It can be concluded that the crystal shape tends to stabilize at n40.30. The stronger peaks appear at 2y ¼33.381, 33.401, 32.941, 33.461 and 33.401, but becomes less than that at 2y ¼33.551 (400) [20]. Because the doping amount of B, Ga, N and F is small, the characteristic peaks shift only a little. There are a few of differences among different upconversion luminescence agents, which suggests the structure of upconversion luminescence agents will not greatly change by doping other ions. It is worth noting that the peak width of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y is wider than that of Er3 þ :Y3Al5O12. It has the similar tendency with Ga, N and F doping Er3þ :Y3Al5O12 shown in Fig. 1(d–f). The peak of Er3þ :Y3BaAl5 aO12 is different from others. As described in Fig. 1c(1–2), the more the doping amount of B the weaker the peaks become. And a new peak appeared at 2y ¼30.521, which might be considered as B2O3 [37]. A strong peak in Fig. 1d(1–2) appears at 2y ¼36.551, which is the characteristic peak of Ga2O3 [38,39]. As the amount of doping ions increases, new peaks become strong as depicted above. Especially, for Er3þ :Yb0.3Y2.7 B1.25Ga1.25Al2.5N0.01F0.01O11.99, its peaks have become high and thin after the ions were doped. In addition, the average crystallite sizes of Er3 þ :YbnY3 n BaGabAl5 a bNxFyO12 x y were roughly estimated by calculation from the width of the XRD peaks using the Scherrer equation [40]: D ¼ K l=bcos y where D is average crystallite size, K represents a constant (0.89), l is the XRD wavelength (0.154 nm), b is the corrected half width of the strongest diffraction peak and y is the diffraction angle. It is apparent that with the increase of temperature the diffraction peaks are appreciably broadened. On the basis of the formula, the particle granularities become thin (about 50 nm). However, when the temperature is 1100 1C, the nano-particle size becomes larger (above 62 nm). In the same way, the average sizes of grainy balls encased on the surface of up-conversion luminescence agent were determined to be approximately 50 nm according to Scherrer formula.
Fig. 1. XRD patterns of Er3 þ :Y3Al5O12 with (a) different doping elements (Yb, B, Ga, N and F) ((a-1) Er3 þ :Yb0.3Y2.7Al5O12; (a-2) Er3 þ :Y3B2.5Al2.5O12; (a-3) Er3 þ :Y3Ga2.5Al2.5O12; (a-4) Er3 þ :Y3Al5N0.01O11.99; (a-5) Er3 þ :Y3Al5F0.01O11.99; (a-6) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98); (b) different Yb molar ratio ((b-1) Er3 þ :Yb0.4Y2.6Al5O12 (n¼ 0.4); (b-2) Er3 þ :Yb0.3Y2.7Al5O12 (n¼ 0.3); (b-3) Er3 þ :Yb0.2Y2.8Al5O12 (n ¼0.2); (b-4) Er3 þ :Yb0.1Y2.9Al5O12 (n¼ 0.1); (b-5) Er3 þ :Yb0.0Y3.0Al5O12 (n¼ 0.0)); (c) different B molar ratio ((c-1) Er3 þ :Y3B2.50Al2.50O12 (a¼ 2.50); (c-2) Er3 þ :Y3B1.25Al3.75O12 (a¼1.25); (c-3) Er3 þ :Y3B0.00Al5.00O12 (a¼ 0.00)); (d) different Ga molar ratio ((d-1) Er3 þ :Y3Ga2.50Al2.50O12 (b¼ 2.50); (d-2) Er3 þ :Y3Ga1.25Al3.75O12 (b ¼1.25); (d-3) Er3 þ :Y3Ga0.00Al5.00O12 (b ¼ 0.00)); (e) different N molar ratio ((e-1) Er3 þ :Y3Al5N0.01O11.99 (x¼ 0.01); (e-2) Er3 þ :Y3Al5N0.005O11.995 (x ¼0.005); (e-3) Er3 þ :Y3Al5N0.00O12.00 (x¼ 0.00)); (f) different N molar ratio (f(-1) Er3 þ :Y3Al5F0.01O11.99 (y¼0.01); (f-2) Er3 þ :Y3Al5F0.005O11.995 (y¼0.005); (f-3) Er3 þ :Y3Al5F0.00O12.00 (y ¼0.00)). (Heat-treated at 1100 1C for 120 min).
L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
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Fig. 2. SEM images of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 1100 1C for 120 min).
SEM morphologies of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y powders heat-treated at 1100 1C for 120 min are shown in Fig. 2. It can be seen clearly that there are a large number of elliptic species with average size about 60 nm, which is similar to the result calculated by Scherrer formula. In comparison, the sizes of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y particles are larger than that of Er3 þ :Y3Al5O12 as shown in SEM images of Fig. 2a. It suggests that the crystal lattice has been enlarged by doping ions with larger diameter. For Er3 þ :Yb0.3Y2.7Al5O12, many round particles can be found in Fig. 2b. Fig. 2c shows rod like nanoparticles with average size of 60–80 nm. Images of Er3 þ :Y3Al5N0.01O11.99 and Er3 þ :Y3Al5F0.01O11.99 particles are depicted in Fig. 2e and f, in which 50 nm homogeneous round particles can be seen. Fig. 2g shows that the diameter of larger grey white particles is about 60 nm, of which slight agglomeration phenomenon was found. It can be also observed that the shapes of them appeared in figures are some what different, such as the surface structure, which may be due to the different structures of modified up-conversion luminescence agents. XPS pattern of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 is shown in Fig. 3, in which the amount and type of doping atoms can be detected. Judging from the full and fine spectrum of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 sample, in addition to three kinds of Y, Al and O elements, apparently, there exists a small amount of Er, Yb, B, Ga, N and F. It can be known that these ions have been doped into the crystal lattice of Y3Al5O12. The element C comes from carbon pollution or the carbon precursor body incompletely removed with XPS test. On the basis of XPS, the molar ratio of Yb, B and Ga is 0.8893%, 0.6302% and 0.5939%, respectively. They are slightly less than theoretical measurement. It would suggest that there is relatively low Yb, B and Ga doped amount near the surface. Still, the molar fraction of N and F is 3.51% and 3.36%, respectively, which is slightly more than perspective doped amount. Thus, N and F are indeed doped into the lattice little of Er3 þ :Y3Al5O12 in the form of ionic morphology. 3.2. XRD and SEM of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y/TiO2 The crystal phases of Er3 þ :Y3Al5O12/TiO2, Er3 þ :Yb0.3Y2.7Al5 O12/TiO2, Er3 þ :Y3B2.5Al2.5O12/TiO2, Er3 þ :Y3Ga2.5Al2.5O12/TiO2, Er3 þ :Y3Al5N0.01O11.99/TiO2, Er3 þ :Y3Al5F0.01O11.99/TiO2 and
Fig. 3. XPS images of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 1100 1C for 120 min).
Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2 were also analyzed by X-ray powder diffractometer in the range of 2y from 101 to 701 shown in Fig. 4. Since the mass ratio of up-conversion luminescence agent is 30% in prepared photocatalyst, the main structure of Y3Al5O12 still can be seen clearly. In comparison with the basic crystal structure of Y3Al5O12, the slight change shows that a small quantity of Er, Yb, B, Ga, N and F ions enter the primary conformation. In addition, new peaks centered at 2y ¼25.341 (1 0 1), 37.941 (0 0 4), 48.241 (2 0 0), 54.021 (1 0 5), 55.161 (2 1 1) and 62.761 (2 0 4) can be observed [41], respectively, which are the characteristic diffraction peaks of anatase phase TiO2 that is the intermediate product with high activity. It could be seen that the characteristic peaks of up-conversion luminescence agent hardly shift, which displays that the crystal change of TiO2 and Er3 þ :Y3Al5O12 are not occurred in the presence of coating of TiO2. And that, no other polymorph was found from the XRD patterns. According to the curve shown in Fig. 4, the peaks of TiO2 and Y3Al5O12 are so high that they have an influence on the performance of up-conversion luminescence agents and the existence of TiO2 makes an impact on the result of the study.
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Fig. 4. XRD patterns of Er3 þ :Y3Al5O12/TiO2 with (a) different doping elements (Yb, B, Ga, N and F) ((a-1) Er3 þ :Yb0.3Y2.7Al5O12/TiO2; (a-2) Er3 þ :Y3B2.5Al2.5O12/TiO2; (a-3)Er3 þ :Y3Ga2.5Al2.5O12/TiO2; (a-4) Er3 þ :Y3Al5N0.01O11.99/TiO2; (a-5) Er3 þ :Y3Al5F0.01O11.99/TiO2; (a-6) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2); (b) different Yb molar ratio ((b-1) Er3 þ :Yb0.3Y2.7Al5O12/TiO2 (n ¼0.3); (b-2) Er3 þ :Yb0.1Y2.9Al5O12/TiO2 (n¼ 0.1); (b-3) Er3 þ :Yb0.0Y3.0Al5O12/TiO2 (n¼0.0)); (c) different B molar ratio ((c-1) Er3 þ :Y3B2.50Al2.50O12/TiO2 (a¼ 2.50); (c-2) Er3 þ :Y3B1.25Al3.75O12/TiO2 (a ¼1.25); (c-3) Er3 þ :Y3B0.00Al5.00O12/TiO2 (a¼ 0.00)); (d) different Ga molar ratio ((d-1) Er3 þ :Y3Ga2.50Al2.50O12/TiO2 (b ¼2.50); (d-2) Er3 þ :Y3Ga1.25Al3.75O12/TiO2 (b ¼1.25); (d-3) Er3 þ :Y3Ga0.00Al5.00O12/TiO2 (b¼ 0.00)); (e) different N molar ratio ((e-1) Er3 þ :Y3Al5N0.01O11.99/TiO2 (x¼ 0.01); (e-2) Er3 þ :Y3Al5N0.005O11.995/TiO2 (x¼ 0.005); (e-3) Er3 þ :Y3Al5N0.00O12.00/TiO2 (x ¼0.00)); (f) different N molar ratio ((f-1) Er3 þ :Y3Al5F0.01O11.99/TiO2 (y ¼0.01); (f-2) Er3 þ :Y3Al5F0.005O11.995/TiO2 (y¼ 0.005); (f-3) Er3 þ :Y3Al5F0.00O12.00/TiO2 (y ¼0.00)). (Heat-treated at 500 1C for 60 min).
The morphologies of TiO2 coating up-conversion luminescence agents, Er3 þ :Y3Al5O12/TiO2, Er3 þ :Yb0.3Y2.7Al5O12/TiO2, Er3 þ :Y3B2.5 Al2.5O12/TiO2, Er3þ :Y3Ga2.5Al2.5O12/TiO2, Er3 þ :Y3Al5N0.01O11.99/TiO2, Er3þ :Y3Al5F0.01O11.99/TiO2 and Er3þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01 O11.98, were characterized by scanning electron microscopy (SEM). In Fig. 5 many grayer spherical particles can be found clearly, which can confirm the rough elliptical form of photocatalyst particles with the average size of 2.0–2.5 mm. In comparison with the SEM shown in Fig. 2, the average size of TiO2 folium is much larger than that of upconversion luminescence agents. It proved that a TiO2 composite particle, in fact, coats many up-conversion luminescence agents particles. Hence, the visible light may sufficiently penetrate through TiO2 folium and excite the inner Er3þ :YbnY3 nBaGabAl5 a b NxFyO12 x y particles, which result in the emission of ultraviolet light. 3.3. Influence of Yb doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 The UV–vis spectra of Er3 þ :Yb0.3Y2.7Al5O12 in the wavelength region of 200–800 nm is detected and the data are shown in Table 1(b). It can be found that in absorption spectra the Er3 þ :Yb0.3Y2.7Al5O12 gives three narrow and strong absorption bands with a maximum at 488 nm, 652 nm and 899 nm, with the corresponding absorbance of 0.052, 0.024 and 0.031, respectively. Although the peak centered at 652 nm is weaker than other two, the absorbance becomes much stronger compared with that of Er3 þ :Y3Al5O12 shown in Table 1(a). The data of up-conversion fluorescence spectrum of Er3 þ : Yb0.3Y2.7Al5O12 in the wavelength of 200–450 nm excited by 488 nm are shown in Table 2-1(b). In principle, the wavelength of the strong emission peaks should be less than 387 nm that can effectively excite TiO2 as photocatalyst. For Er3 þ :Yb0.3Y2.7Al5O12, a peak centered at 317 nm is corresponding to the transition of 2 P3/2-4I15/2 [21,42] with fluorescence intensity of 3.63 104 mau
and full width at half maximum (FWHM) of 10 nm. Apparently, the fluorescence spectrum of Er3 þ :Yb0.3Y2.7Al5O12 gives wider and stronger emission peaks than those of Er3 þ :Y3Al5O12 shown in Table 2-1(a). It suggests that the performance of modified upconversion luminescence agent is better than before. The emission peak at 403 nm is associated with transitions of 2P3/ 2 2- I13/2 [21,42,43] and another peak at 429 nm attributes to the transition of 2G9/2-4I15/2 [21,42] whose FWHM are 3.0 nm and 1.0 nm wider and intensity are 0.20 105 mau and 0.32 105 mau, respectively. Obviously, they are stronger than data shown in Table 2-1(a). In other word, because of Yb doping the peaks all become stronger and wider than those of Er3 þ :Y3Al5O12. Table 2-2(b) shows that the intensities of the emission peaks at 246 nm corresponding to 3I4-3P5/2 [44] and 497 nm related to 4 S3/2-4I15/2 [44], with 1.42 104 mau and 3.28 104 mau, respectively, are not so strong compared with that of Er3 þ :Y3Al5O12 shown in Table 2-2(a). However, the peak at 588 nm which belongs to 2G9/2-4I13/2 [44] is strong enough. Furthermore, the FWHM of three peaks shown in Table 2-3(b) are all wider than those shown in Table 2-3(a). The emission peak at 491 nm which is assigned to 4F7/2-4I15/2 [10,46] is much stronger than corresponding that of Er3 þ :Y3Al5O12. And that, the peaks at 268 nm and 426 nm corresponding to 4G7/2-4I15/2 and 2G9/2-4I15/2 [10,45], respectively, are similar to those displayed in Table 2-3(a). The emission peak at 491 nm which is assigned to 4 F7/2-4I15/2 [10,46] is much strong. In any case, the doped Yb ion as a sensitizer plays a certain role in enlarging the spectrum range and intensity to some extent. 3.4. Influence of B and Ga doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 The data of absorption and emission spectra of Er3 þ :Y3B2.5 Al2.5O12 and Er3 þ :Y3Ga2.5Al2.5O12 shown in Table 1(c) and (d) and Table 2(c) and (d) suggest that spectra of modified up-conversion
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Fig. 5. SEM images of (a) Er3 þ :Y3Al5O12/TiO2; (b) Er3 þ :Yb0.3Y2.7Al5O12/TiO2; (c) Er3 þ :Y3B2.5Al2.5O12/TiO2; (d) Er3 þ :Y3Ga2.5Al2.5O12/TiO2; (e) Er3 þ :Y3Al5N0.01O11.99/TiO2; (f) Er3 þ :Y3Al5F0.01O11.99/TiO2; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2. (Heat-treated at 500 1C for 60 min).
Table 1 Characteristic absorption spectra of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 500 1C for 60 min). Sample
First absorption peak
Second absorption peak
(No:)
Peak position (nm)
Absorbance (au)
Peak position (nm)
Absorbance (au)
Peak position (nm)
Absorbance (au)
a b c d e f g
488 488 488 488 488 488 488
0.009 0.052 0.029 0.023 0.029 0.040 0.058
653 652 648 648 650 650 649
0.014 0.024 0.051 0.014 0.019 0.032 0.042
896 899 898 893 893 899 898
0.002 0.031 0.053 0.012 0.021 0.028 0.042
luminescence agents are improved compared with that of Er3 þ :Y3Al5O12 shown in Table 1(a) and Table 2(a). It indicates that doping B and Ga makes an effect on enhancing spectrum intensity. The absorption spectrum of Er3 þ :Y3B2.5Al2.5O12 shown in Table 1(c) displays an obvious increase in peak width. The same phenomenon can be seen in Table 1(d), and peaks centered at 488 nm, 648 nm and 893 nm all become stronger than that Er3 þ :Y3Al5O12 of in Table 1(a). It is desirable that the emission spectra within ultraviolet range are strong enough to stimulate TiO2, which could increase the utilization rate of solar light. In Table 2-1(c), it can be seen that the peaks centered at 403 nm and 429 nm do not change compared with those in Table 2-1(a), but the peak centered at 318 nm becomes stronger than that in Table 2-1(a). In Table 2-2(c), the emission peaks at 492 nm and 582 nm become strong and FWHM of peaks at 246 nm and 582 nm become wide obviously. It indicates that doped B enhances the peak intensity and width to some extent. In Table 2-3(c), the peak at 260 nm which shifts a little is wider than that at the same wavelength in Table 2-3(a). The characterized peaks all become wide and that the peaks at 421 nm and 495 nm become strong enough. As shown in Table 2-1(d), the peak centered at 429 nm is much stronger than that in Table 2-1(a). In Table 2-2(d), all peak widths become wide by 2–4 nm, whereas only the peak at 582 nm is not so strong. In Table 2-3(d), all peak widths broaden much, but the peak intensities hardly change.
Third absorption peak
3.5. Influence of N and F doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 As seen in Table 1(e), all absorption peaks of Er3 þ :Y3Al5N0.01 O11.99 become strong. Especially, the absorbance at 488 nm and 893 nm are intensified by a large margin, with amplification of 0.020 and 0.019, respectively. The absorbance of Er3 þ :Y3Al5F0.01 O11.99 in Table 1(f) increase to 0.031, 0.018 and 0.026, respectively, but the peak positions do not express obvious changes. It indicates that doping of N and F makes more visible light convert into ultraviolet light. In Table 2-1(e) and (f), the emission peaks at l ¼319 nm, 404 nm and 429 nm are somewhat similar to the data in Table 2-1(a), but their FWHM becomes wider by 3–6 nm. Especially, the first emission peak becomes very wide and the wavelength range is from l ¼317 nm to l ¼ 319 nm. Table 2-1(e) shows the similar peak position to Table 2-1(a), but the ultraviolet light emission peak in the wavelength region of 340–400 nm is wider than that of Er3 þ :Y3Al5O12. In Table 2–2(e), the intensity of the ultraviolet light emissions at l ¼246 nm is not so strong but the FWHM was enlarged by 5 nm. Nevertheless, both the peak width and intensity of the other two peaks are enhanced largely. In Table 2-3(e), the FWHM are all enlarged by 3–5 nm, whereas only the peak intensity at 426 nm becomes very strong. As shown in Table 2-1(f), the peak intensity becomes much strong compared with that of Er3 þ :Y3Al5O12 and the FWHM also becomes
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Table 2 Characteristic emission spectra of (a) Er3 þ :Y3Al5O12; (b) Er3 þ :Yb0.3Y2.7Al5O12; (c) Er3 þ :Y3B2.5Al2.5O12; (d) Er3 þ :Y3Ga2.5Al2.5O12; (e) Er3 þ :Y3Al5N0.01O11.99; (f) Er3 þ :Y3Al5F0.01O11.99; (g) Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98. (Heat-treated at 500 1C for 60 min). Sample
2
P3/2-4I15/2
(No:)
Peak position (nm)
P3/2-2I13/2
Half band width (nm)
Intensity Peak position (104 ma.u) (nm)
(1) Under 488 nm excitation A 317 9 B 317 10 C 318 10 D 319 13 E 318 15 F 319 15 G 312 10.5 3 Sample I4-3P5/2 (No:) Peak position Half band width (nm) (nm)
3.25 3.63 3.27 3.25 3.22 3.77 3.02
404 403 403 404 404 403 404
Intensity (104ma.u)
Peak position (nm)
(2) Under 653 nm excitation A 246 6 B 246 7 C 246 13 D 235 10 E 246 11 F 245 12 G 220 10 4 Sample G7/2-4I15/2 (No:) Peak position Half band width (nm) (nm)
1.42 1.42 1.06 2.13 1.38 0.52 0.44
496 497 492 496 497 494 497
Intensity (102ma.u)
Peak position (nm)
(3) Under 900 nm excitation A 266 5 B 268 6 C 260 7 D 255 7 E 266 10 F 262 10 G 269 9
2.91 0.67 1.24 0.92 1.85 1.08 2.55
426 426 421 426 426 420 425
G9/2-4I15/2
2
2
Half band width Intensity (nm) (105ma.u)
Peak position (nm)
Half band width (nm)
Intensity (105ma.u)
8 11 14 12 12 12 14 4 S3/2-4I15/2 Half band width (nm)
1.55 1.75 1.51 1.56 1.50 1.70 1.39
432 429 429 429 429 429 429
2.31 2.63 2.28 2.41 2.31 2.59 2.11
Intensity (104ma.u)
Peak position (nm)
9 10 9 10 12 12 14 2 G9/2-4I13/2 Half band width (nm)
3.28 3.28 3.03 3.31 3.93 3.87 0.67
580 588 582 582 588 584 587
4 6 12 13 9 9 11
Intensity (104ma.u)
Peak position (nm)
4 F7/2-4I15/2 Half band width Intensity (nm) (102ma.u)
3.28 3.28 3.03 1.31 3.93 3.87 0.67
495 491 495 502 493 493 495
5 6 7 8 11 8 9
5 7 5 8 10 5 11 2 G9/2-4I15/2 Half band width (nm)
6 7 10 7 10 11 12
Intensity (104ma.u)
3.35 4.64 4.26 2.04 4.83 5.34 1.10
17.10 37.00 42.31 3.76 5.86 3.64 17.93
wide in a large scale. In Table 2-2(f), both of the emission peak intensity and FWHM are enhanced more or less, which indicates the doping F ion makes the emission peaks become wide and strong. In Table 2-3(f), FWHM all become wide and only peak at 420 nm become strong, which suggests that the doping N or F ion might not enhance both the peak intensity and width at the same time. 3.6. Influence of Yb, B, Ga, N and F co-doping on light absorption and luminescence characters of Er3 þ :Y3Al5O12 In Table 1(g), the absorption peaks at 488 nm, 649 nm and 898 nm are all very strong. In fact, the absorbance becomes quite intense compared to that (Table 1(a)) of Er3 þ :Y3Al5O12. The appealing result is the anti-stokes emission under 400 nm wavelength excitation, which displays an enhancement for up-conversion effect of Er3 þ :Y3Al5O12. It suggests that the modified upconversion luminescence agents make more visible light converted to ultraviolet light. At last, as a special case the fluorescence emission spectrum of Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 under excitation of 488 nm wavelength light was given in Fig. 6. For comparison, the fluorescence emission spectrum of Er3 þ :Y3Al5O12 was also provided in Fig. 6. Particularly, the emission spectra in the range of 200–450 nm which is matching with the energy band gap (Ebg ¼3.2 eV) of TiO2 was researched. As depicted in Fig. 6, all emission peaks of modified up-conversion luminescence agent (Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98) become stronger and wider than ones of Er3 þ :Y3Al5O12, which indicates the effects
Fig. 6. Fluorescence emission spectra (lex ¼488 nm) of Er3 þ :Y3Al5O12 (a) and Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98 (g).
of co-doping ions (Yb, B, Ga, N and F) once again. In detail, as shown in Table 2-1(g), the peak intensity becomes slightly strong but the peak width is much enlarged. The emission peaks at 312 nm, 404 nm and 429 nm were broadened by 1.5 nm, 6.0 nm and 5.0 nm, respectively. In Table 2-2(g), the same variation trend can be seen. It suggests that more emission light was converted. In Table 2-3(g), the emission peaks become a little wide but the peak intensity only at 495 nm becomes strong. In sum, the intensity and width of emission spectra are both improved in a
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photocatalysts reveal high photocatalytic activity in the degradation of organic dyes.
4. Conclusions
Fig. 7. Degradation of different dyes (with up-conversion luminescence agent: TiO2 ¼3: 10 (heat-treated at 500 1C for 60 min) amount, 24–28 1C temperature and 120 min solar light irradiation). (a) Er3 þ :Y3Al5O12/TiO2; (b) Er3 þ :Yb0.3Y2.7 Al5O12/TiO2; (c) Er3 þ :Y3B1.25Al3.75O12/TiO2; (d) Er3 þ :Y3Ga1.25Al3.75O12/TiO2; (e) Er3 þ :Y3Al5N0.005O11.995/TiO2; (f) Er3 þ :Y3Al5F0.005O11.995/TiO2; (g) Er3 þ :Yb0.3 Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2.
large scale. The doping ions serve as strengthening and widening spectra for up-conversion luminescence agents. 3.7. Photocatalytic activity of Er3 þ :YbnY3 nBaGabAl5 a bNxFyO12 x y in degradation of organic dyes under solar light irradiation The degradation ratio was detected by UV–vis spectrometer because the absorbance of ordinary dye solution with low concentration abides by Lambert–Beer Law. The degradation ratio of different organic dyes under solar light irradiation (21–25 1C temperature, 8.00–10.00 a.m. and 2.00–4.00 p.m. every day in June, E1231270 and N711500 , Shenyang City, China) is shown in Fig. 7. After 60 min, with fragmentation of the azo bonds and naphthyl rings attacking, obvious degradation rate is obtained. Anyway, these results suggest that these dye molecules were already decomposed. In addition, under the same solar light irradiation the degradation ratio is much higher in the presence of Er3 þ :Ybn Y3 nBaGabAl5 a bNxFyO12 x y/TiO2 compared to that in the presence of Er3 þ :Y3Al5O12/TiO2. Apparently, that is because the doping of Yb, B, Ga, N and F enhances the visible light absorption capability and ultraviolet light emission intensity of Er3 þ : Y3Al5O12, which further improves the photocatalytic activity of TiO2. These doping atoms demonstrate a good synergistic effect during up-conversion luminescence process, which is in accordance with the deduction ratios of various organic dyes in Fig. 7. Of course, due to the different molecule structures and chemical compositions, these used organic dyes show different degradation ratios. Methylene Blue was easy to degrade for the high photosensitivity. On the other hand, the degradation of Rhodamine B was lower than other dyes. In any way, all selected organic dyes could be degraded to some extent. It indicates the prepared TiO2 photocatalyst coating up-conversion luminescence agents should be broad-spectrum in photocatalytic degradation of various organic dyes. On the whole, for all used organic dyes, the degradation ratio in the presence of Er3 þ :Yb0.3Y2.7B1.25Ga1.25 Al2.5N0.01F0.01O11.98 is highest. The enhancement of the photocatalytic activity is due to the performance of modified up-conversion luminescence agents with other ions. The participation of other doped ions made the absorption and emission spectra become wider more or less, which leads to more transformation of visible light in solar spectra to ultraviolet light. Thus, the modified
The study aims at investigating the effect of some doping elements into Er3 þ :Y3Al5O12 on the luminescence characteristics and the photocatalytic performance of the corresponding Er3 þ :Y3Al5O12/TiO2 composites. In summary, we have developed an important synthesis of up-converted luminescence agents (Er3þ : Y3Al5O12, Er3 þ :YbnY3 nAl5O12, Er3 þ :Y3BaAl5 aO12, Er3 þ :Y3Gab Al5 bO12, Er3 þ :Y3Al5NxO12 x, Er3 þ :Y3Al5FyO12 y and Er3þ :YbnY3 n BaGabAl5 a bNxFyO12 x y) and their corresponding photocatalysts with TiO2 coating (Er3 þ :Y3Al5O12/TiO2, Er3 þ :YbnY3 nAl5O12/TiO2, Er3 þ :Y3BaAl5 aO12/TiO2, Er3 þ :Y3GabAl5 bO12/TiO2, Er3þ :Y3Al5Nx O12 x/TiO2, Er3þ :Y3Al5FyO12 y/TiO2 and Er3 þ :YbnY3 nBaGab Al5 a bNxFyO12 x y/TiO2). These prepared up-converted luminescence agents can present wide excitation wavelength and then produce strong emission peaks via the effective up-conversion process. That is, ultraviolet, violet and blue up-conversion luminescence emissions of Er3 þ :YbnY3 nGaaBbAl5 a bNxFyO12 x y could be observed under 488 nm, 654 nm and 900 nm light excitation. Judging from the result, the process is particularly effective when the Er3 þ :Y3Al5O12 is doped with Yb, B, Ga, N and F together. It should be noted that Yb as a sensitizer in the host lattice makes a significant contribution to the up-conversion emission and absorption spectra. Up-conversion luminescence agents doped with N and F exhibit somewhat spanning of deep UV regions light. And B and Ga make the absorption and emission peaks become strong in the results. At last, the prepared TiO2 coated composites are used to detect the photocatalytic degradation ratio of some organic dyes. It indicates that the photocatalytic activity of TiO2 can be enhanced obviously by modified up-conversion luminescence agents in dyes degradation. Of which, the Er3 þ :Yb0.3Y2.7B1.25Ga1.25Al2.5N0.01F0.01O11.98/TiO2 displays the most effective photocatalytic activity in dyes degradation under solar light irradiation.
Acknowledgments The authors greatly acknowledge the National Natural Science Foundation of China, Liaoning Province Natural Science Foundation of Education Department, Liaoning Province Natural Science Foundation of Science and Technology Department and Liaoning university ‘‘211’’ project for financial support. The authors also thank our colleagues and other students for their participating in this work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
C.M. So, M.Y. Cheng, J.C. Yu, P.K. Wong, Chemosphere 46 (2002) 905. C. Debabrata, M. Anima, J. Photochem. Photobiol., A 153 (2002) 199. C. Karunakaran, R. Dhanalakshmi, Sol. Energy Mater. Sol. Cells 92 (2008) 588. J. Wang, Y.H. Lv, L.Q. Zhang, B. Liu, R.Z. Jiang, G.X. Han, R. Xu, X.D. Zhang, Ultrason. Sonochem. 17 (2010) 642. X.W. Zhang, L.C. Lei, J.L. Zhang, Q.X. Chen, J.G. Bao, B. Fang, Sep. Purif. Technol. 67 (2009) 50–57. X.F. You, F. Chen, J.L. Zhang, M. Anpo, Catal. Lett. 102 (2005) 247. N. Barka, S. Qourzal, A. Assabbane, A. Nounah, Y. Aˆıtichou, J. Photochem. Photobiol., A: Chem 195 (2008) 346. R. Comparelli, E. Fanizza, M.L. Curri, P.D. Cozzolia, G. Mascoloc, A. Agostiano, Appl. Catal., B: Environ 60 (2005) 1. J. Wang, G. Zhao, Z.H. Zhang, X.D. Zhang, G. Zhang, T. Ma, Y.F. Jiang, P. Zhang, Y. Li, Dyes Pigm. 75 (2007) 335. R. Francini, S. Pietrantoni, M. Zambelli, A. Speghini, M. Bettinelli, J. Alloys Compd. 380 (2004) 34. W.J. Tobler, W. Durisch, Appl. Energy 85 (2008) 483. H.M.H. Fadlalla, C.C. Tang, J. Cryst. Growth 311 (2009) 3737. D. Jaque, J. Capmany, F. Molero, Z.D. Luo, J.G. Sole, Opt. Mater. 10 (1998) 211.
3018
L. Yin et al. / Journal of Luminescence 132 (2012) 3010–3018
[14] Z.G. Hu, M. Yoshimura, Y. Mori, T. Sasaki, K. Kato, Opt. Mater. 23 (2003) 353. [15] J. Wang, J. Li, Y.P. Xie, C.W. Li, G.X. Han, L.Q. Zhang, R. Xu, X.D. Zhang, J. Environ. Manage. 91 (2010) 677. [16] V. Mahalingam, F. Vetrone, R. Naccache, A. Speghini, J.A. Capobianco, Adv. Mater. 21 (2009) 4025. [17] M. Szachowicz, S. Tascu, M.F. Joubert, P. Moretti, M. Nikl, Opt. Mater. 28 (2007) 162. [18] J. Wang, F.Y. Wen, Z.H. Zhang, X.D. Zhang, Z.J. Pan, P. Zhang, P.L. Kang, J. Tong, L. Wang, L. Xu, J. Photochem. Photobiol., A 180 (2007) 189. [19] R. Xu, J. Li, J. Wang, X.F. Wang, B. Liu, B.X. Wang, X.Y. Luan, X.D. Zhang, Sol. Energy Mater. Sol. Cells 94 (2010) 1157. [20] J. Wang, R.H. Li, Z.H. Zhang, W. Sun, R. Xu, Y.P. Xie, Z.Q. Xing, X.D. Zhang, Appl. Catal., A 334 (2008) 227. [21] N.N. Zu, H.G. Yang, Z.W. Dai, Physica B 403 (2008) 174. ¨ zen, O. Forte, B. Di Bartolo, Opt. Mater. 27 (2005) 1664. [22] G. O [23] D. Sangla, N. Aubry, A. Nehari, A. Brenier, O. Tillement, K. Lebbou, F. Balembois, P. Georges, D. Perrodin., J. Didierjean, J.M. Fourmigue, J. Cryst. Growth 312 (2009) 125. [24] L.A. Diaz-Torrdes, E. De la Rosa, P. Salas, H. Desirena, Opt. Mater. 27 (2005) 1305. [25] X.D. Wang, X.D. Xu, Z.W. Zhao, B.X. Jiang, J. Xu, G.J. Zhao, P.Z. Deng, G. Bourdet, J.C. Chanteloup, Opt. Mater. 29 (2007) 1662. ¨ ¨ [26] J.F. Suyver, J. Grimm, K.W. Kramer, H.U. Gudel, J. Lumin. 114 (2005) 53. [27] L.F. Liang, X.M. Zhang, H.L. Hu, L. Feng, M.M. Wu, Q. Su, Mater. Lett. 59 (2005) 2186. [28] G. Dominiak-Dzik, P. Solarz, W. Ryba-Romanowski, E. Beregi, L. Kova´cs, J. Alloys Compd. 359 (2003) 51. [29] P.Y. Jia, J. Lin, X.M. Han, M. Yu, Thin Solid Films 483 (2005) 122.
[30] X.P. Chen, Q.Y. Zhang, C.H. Yang, D.D. Chen, C. Zhao, Spectrochim. Acta, Part A 74 (2009) 441. [31] Z.Q. Li, Y. Zhang, S. Jiang, Adv. Mater. 24 (2008) 4765. [32] M. Dulick, G.E. Faulkner, N.J. Cockroft, D.C. Nguyen, J. Lumin. 48–49 (1991) 517. [33] S. Nicolas, E. Descroix, M.F. Joubert, Y. Guyot, M. Laroche, R. Moncorge´, R. Yu Abdulsabirov, A.K. Naumov, V.V. Semashkod, A.M. Tkachuke, M. Malinowskif, Opt. Mater. 22 (2003) 139. [34] D.V. Arkhipov, T.I. Khristov, N.V. Popovich, S.S. Galaktionov, N.P. Soshchin, Inorg. Mater. 32 (1996) 459. [35] F.E. Ghodsi, F.Z. Tepehan, G.G. Tepehan, Sol. Energy Mater. Sol. Cells 92 (2008) 234. [36] J. Wang, Y.P. Xie, Z.H. Zhang, J. Li, X. Chen, L.Q. Zhang, R. Xu, X.D. Zhang, Sol. Energy Mater. Sol. Cells 93 (2009) 355. [37] Z.B. Hu., H.J. Li., Q.G. Fu., H. Xue, G.L. Sun, New Carbon Mater. 22 (2007) 131. [38] H.F. Jiang, Y.Q. Chen, Q.T. Zhou, Y. Su, H.H. Xiao, L.A. Zhu, H.F. Jiang, Mater. Chem. Phys. 103 (2007) 14. [39] B.C. Kim, K.T. Sun, K.S. Park, K.J. Im, T. Noh, M.Y. Sung, S. Kim, S. Nahm, Y.N. Choi, S.S. Park, Appl. Phys. Lett. 80 (2002) 479. [40] P.F.S. Pereira, J.M.A. Caiut, S.J.L. Ribeiro, Y. Messaddeq, K.J. Ciuffia, L.A. Rocha, E.F. Molina, E.J. Nassar, Ceram. Int. 126 (2007) 378. [41] J.Q. Gao, R.Z. Jiang, J. Wang, B.X. Wang, K. Li, P.L. Kang, Y. Li, X.D. Zhang, Chem. Eng. J. 168 (2011) 1041. [42] H.L. Xu, Z.K. Jiang, Chem. Phys. 287 (2003) 155. [43] S. Du, J.X. Xu, X.R. Dong, J. Zhang, Z.L. Fu, Z.W. Dai, J. Lumin. 130 (2010) 872. [44] H.G. Yang, Z.W. Dai, Z.W. Sun, J. Lumin. 124 (2007) 207. [45] G.Y. Chen, Y. Liu, Z.G. Zhang, B. Aghahadi, G. Somesfalean, Q. Sun, F.P. Wang, Chem. Phys. Lett. 448 (2007) 127.