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Excellent green emission of Tb3+ incorporated in MgAl–NO3 layered double hydroxides system
Journal of Luminescence 181 (2017) 71–77
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Excellent green emission of Tb3 þ incorporated in MgAl–NO3 layered double hydroxides system Yufeng Chen n, Yao Bao, Zhipeng Yu, Guangchao Yang, Ling Zhang College of Chemistry, Nanchang University, Nanchang 330031, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 August 2015 Received in revised form 26 August 2016 Accepted 27 August 2016 Available online 31 August 2016
A series of Tb-doped MgAl–NO3 layered double hydroxides (LDHs) with Mg2 þ /(Al3 þ þTb3 þ ) molar ratios ranging from 1.0 to 4.0 were synthesized through co-precipitation method at room temperature. X-ray diffraction (XRD) results indicated that the crystallinity of all the Tb-doped samples presented a single phase corresponding to LDHs. SEM measurement suggested that all the samples have similar morphologies. Fluorescence spectra show strong green emissions at 490 and 544 nm, ascribed to the 5 D4-7F6 and 5D4-7F5 transition of Tb3 þ , respectively. This result revealed that the MgAl–NO3 LDH system was favorable for the green emissions of Tb3 þ ions. & 2016 Elsevier B.V. All rights reserved.
Keywords: MgAl-LDHs Tb3 þ -doped Co-precipitation method Fluorescence
1. Introduction Rare-earth doped materials, such as nanocrystals or organic complexes, have been extensive studies owing to their luminescence properties [1–6]. In particular, Eu(III) and Tb(III) complexes have attracted attention due to their well-defined luminescence properties, including hypersensitivity to the coordination environment, and narrow bandwidth [7–11]. In comparison with that of trivalent europium ion, the study on luminescent property of trivalent terbium ion is limited. Moreover, most studies on the fluorescence of trivalent terbium ions focus on its organic complexes [12–18], and reveal the energy transfer from organic ligand to Tb (III) occurred in the Tb (III) complexes [16,18]. In view of the thermal and chemical stability as well as less environmental pollution, the investigation about Tb (III) doped inorganic materials is still worthwhile to be paid attention. Despite some reports on the studies of Tb-doped inorganic materials, the preparation of materials related to sintering process at high temperature is in need of much energy consumption [19,20]. Therefore, it is important to prepare the Tb-doped inorganic materials at room temperatures, especially for inorganic layered double hydroxides that are potential application in biological technology. However, some studies on Tb-complex ions intercalated into layered double hydroxides were developed. For example, Zhuravleva et al. have investigated the luminescent hybrid materials based on mixed Eu/Tb n
Corresponding author. Fax: þ 86 791 3969514. E-mail address: [email protected] (Y. Chen).
http://dx.doi.org/10.1016/j.jlumin.2016.08.060 0022-2313/& 2016 Elsevier B.V. All rights reserved.
complexes intercalated into Mg–Al LDH [21], and revealed highly efficient ligand-Tb3 þ /Eu3 þ and Tb3 þ -Eu3 þ communication channels; Liu et al. have studied the intercalation of organic sensitizer guests into layered Tb(OH)3, and found synergistic effects in luminescence enhancing and tuning [22]. In order to better apply the fluorescence of Tb3 þ to biological technology, along with our successful experiences of Eu ion doped onto layers of LDHs [23,24], we have further incorporated Tb3 þ onto the brucite-like octahedral layers of MgAl-LDH, and found strong green emission of the Tb3 þ doped into layers of MgAl-LDH. This Tb incorporated onto the layers of LDHs is more favorable for touching outside environment compared with the Tb incorporated into interlayer space of LDHs, which is very important as a fluorescent probe for the potential application in biological technology. The Tb-doped layered double hydroxides should more high thermal stability and less toxicity compared with those Tb–organic complexes.
2. Experimental 2.1. Samples preparation Mg(NO3)2 6H2O, Al(NO3)3 9H2O, Tb2O3, NH3 H2O, and HNO3 were of A.R. grade, and were purchased from Chemistry Reagent Corporation of National Medicine Group. Tb(NO3)3 solution (0.05 mol L 1) was prepared by Tb2O3 solid dissolved in mixed solution of HNO3 and H2O2. In order to keep a constant Tb/(Al þTb) ratio of 0.06, but vary the Mg/(Al þTb) ratio, the amount of Mg (NO3)2 and Al(NO3)3 was adjusted for each sample. That is, a mixed
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solution with the Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratios of 1.0, 2.0, 3.0, and 4.0, and an constant Tb3 þ /(Al3 þ þ Tb3 þ ) molar ratio of 0.06, was obtained by dissolving Mg(NO3)2 6H2O and Al(NO3)3 9H2O solid in dilute HNO3 and joining Tb(NO3)3 solution. Then, a series of Tb-doped MgAl–NO3 layered double hydroxides precipitate produced by the addition of a 3.0 mol L 1 NH3 solution. After precipitation (pH ¼8–9), the suspension aged at 40 °C for two hours, then the slurry was filtrated, washed with deionize water, and dried at 70 °C for 24 h. The MgAl–NO3 samples with Mg2 þ /(Al3 þ þTb3 þ ) molar ratios of 1.0, 2.0, 3.0, and 4.0 were signed as MgAl-Tb-LDH-1, MgAl-Tb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4, respectively. A binary MgAl-LDH with Mg2 þ /Al3 þ molar ratio of 2.0 was prepared by the same method as above. Tb (OH)3 was prepared with above Tb(NO)3 solution (0.05 mol L 1) and NH3 solution (3.0 mol L 1) by precipitation. In order to avoid carbonate contamination, the CO2-free deionized water was used in all the experiments.
range of errors. These results are similar to those of literatures [25–27]. The XRD patterns of synthesized Mg-Al-Tb-LDHs and Tb(OH)3 are shown in Fig. 1. All the samples exhibit a low crystallinity in view of the synthesis conditions (at room temperature, fast addition, aged for 2 h at 40 °C). For the Mg-Al-Tb-LDHs, the main diffraction peaks are in good agreement with the characteristics of hexagonal phase [26]. The position of the first 00l diffraction line situated in the low angle region (2θ) is relevant to the interlayer distance (d) and mainly depends on the size of the intercalated anion. The interlayer distances (d003 ¼9.07–8.81 Å) of all samples are consistent with the presence of NO3 intercalated anions [27,28] (Table 2), but are larger than those of MgAl–CO3 LDHs in
2.2. Characterization techniques Chemical contents of Mg, Al, and Tb were determined by inductively coupled plasma atomic emission spectroscopy (ICPAES Optima 5300DV American Pe Company, America). Scanning electron microscope (SEM, JEOL JSM-6701F, JEOL Company, Akishima, Tokyo, Japan) was employed for the morphology analysis of all the samples. X-ray diffraction (XRD) patterns were performed by a X-ray diffractometer using CuKα radiation (XD-3, Beijing Puxi Tongyong Yiqi Ltd. China). All the samples were scanned in the 2θ range of 4–70° at a scan rate 2°/min. Fourier transform infrared (FTIR) spectra of the solid materials were obtained with Shimadzu IR Prestige-21 FTIR spectrometer by the KBr method. Thermogravimetric (TG) and differential thermogravimetric (DTG) data were collected using synchronous thermal analyzer (PYRIS DIAMOVD, AMERICAN PE COMPANY) under a flowing nitrogen atmosphere at a scan rate of 10 °C/min. The fluorescence of the samples was investigated with the help of F-7000 FL Spectrophotometer.
3. Results and discussion 3.1. Structural and compositional analysis A series of three intra-layer cations LDH incorporating small Tb3 þ by substitution of Al3 þ in a MgAl–NO3 LDHs phase were synthesized by the co-precipitation route at room temperature. The Tb3 þ /(Al3 þ þTb3 þ ) molar ratio was maintained constant at 0.06. From ICP-AES elemental analysis, chemical composition of the as-prepared samples agreed well with those expected based on the composition of the reaction mixtures (Table 1). It is worth noting that although the Mg2 þ /(Al3 þ þTb3 þ ) molar ratio determined from ICP-AES analysis differs from the initial Mg2 þ / (Al3 þ þ Tb3 þ ) molar ratio, the difference is within the reasonable Fig. 1. XRD patterns of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-Tb-LDH-2, (d) MgAl-Tb-LDH-3, (e) MgA-Tb-LDH-4, and (f) Tb(OH)3.
Table 1 Chemical composition of samples by ICP-AES. Samples
MgAl-LDH MgAl-Tb-LDH-1 MgAl-Tb-LDH-2 MgAl-Tb-LDH-3 MgAl-Tb-LDH-4
Mg(Al þ Tb) molar ratio
Tb/(Al þTb) molar ratio
Initial
Experimental
Initial
Experimental
2.00 1.0 2.00 3.00 4.00
1.98 1.01 2.01 2.97 3.96
0.06 0.06 0.06 0.06 0.06
0.06 0.06 0.06 0.06 0.06
Table 2 Lattice parameters of all MgAl-LDH and MgAl-Tb-LDH-n (n¼1,2,3,4). Lattice parameters
MgAl-LDH
Tb-LDH-1
Tb-LDH-2
Tb-LDH-3
Tb-LDH-4
a c
3.202(3) 27.08(9)
3.207(4) 26.99(2)
3.200(1) 26.968(8)
3.199(4) 26.51(6)
3.253(3) 26.57(6)
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Fig. 2. SEM images of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-Tb-LDH-2, (d) MgAl-Tb-LDH-3, and (e) MgAl-Tb-LDH-4.
consideration of the different ionic Radii of NO3 (2.3 Å) and CO32 (1.74 Å) [29–32]. The (0 0 3), (0 0 6) and (0 0 9) peaks of all samples appeared at about 10.2°, 20.1°, and 35.0° respectively. The (1 1 0) peaks of all samples, which represent layer structure, appeared at about 61.7°. Cell parameters c and a, which reflect the interlayer and cation-cation distances, were calculated from the 003 and 110 peak positions, assuming 3R stacking [25,33]. The basal distances of d (0 0 3) for all samples are 9.03–8.81 Å and those of d (1 1 0) are 1.50–1.52 Å. The value of the cell parameter a is about two times of the d110 (seen in Table 2) for all the Mg-AlTb-LDHs, which is in agreement with those of previous reports [25,33]. With regard to the Tb(OH)3, the major peaks assigned to (1 0 0), (1 0 1), (0 0 2), and (2 2 0) planes of the hexagonal crystal structure were found (JCPDS 01-083-2038). Meanwhile, an undefined impurity peak (assigned as *) appeared. This impurity peak was also observed in the Tb(OH)3 phase prepared by Sohn [34]. In the light of the diffraction intensity of XRD, the crystallinity of the Tb-doped LDH tended to be better while the Mg2 þ / (Al3 þ þTb3 þ ) molar ratio varied from 1.0 to 4.0. No phase corresponding to Tb(OH)3 (Fig. 1(f)) [34] or other Tb3 þ -contained compounds was observed. This indicated that the Tb3 þ ions should be isomorphously present in the brucite-like layer because of their favorable ionic radii (Tb3 þ 0.92 Å, Al3 þ 0.51 Å, and
Mg2 þ 0.66 Å). The crystallographic parameters of the ternary MgAl-Tb-LDHs and binary MgAl-LDH were refined basing on the XRD data (seen in Table 2) and literatures [28,29]. Small differences appeared in all samples. In general, the parameter c can be affected by various factors such as the amount of interlayer water and anions, Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratio, and the crystallinity of the samples, etc. It is very complicated to define these influencing factors. It is noteworthy that the SEM images (seen in Fig. 2) of all the samples are neither the hexagonal platelike synthesized by hydrothermal reaction [26,29,35,36] nor other morphologies reported [37], but similar to the previous MgAl–NO3 [28]. These morphological differences may be due to different preparing conditions or processes. Meanwhile, FT-IR spectroscopy (Fig. 3) shows a strong sharp band at 1386 cm 1 attributed to stretching vibrations of NO3 ions [38–40], a broad strong band at 3445 cm 1 along with a weak sharp band at 1642 cm 1 ascribed to O–H stretching and bending modes from layer and the interlayer water molecules [41]. The bands at 654 and 444 cm 1 are due to metal–oxygen vibration [24,42]. All these results indicated the formation of the Tb-doped MgAl–NO3 LDHs. It was worthwhile to notice that the bands at 2973 and 1049 cm 1 only appeared in the MgAl-Tb-LDH-3, but were not found in other MgAl-Tb-LDHs.
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The reason is that the bands at 2973 and 1049 cm 1 are attributed to ethanol which is used as a cleaning agent during measurement. 3.2. Thermogravimetry and differential thermogravimetry (TG–DTG) Fig. 4 shows the TG and differential thermal gravimetry (DTG) curves obtained for all the samples, and the corresponding mass loss stages present in Table 3. The decomposition of MgAl-LDH occurred in the following four stages: stage 1, mass loss of 0–10.46% until 145 °C, corresponded to the evaporation of surface adsorbed water and interlayer water in MgAl-LDH; stage 2, mass loss of 10.46–19.71% at 145–320 °C; stage 3, mass loss of 19.71– 37.45% at 320–486 °C. The second and third stages were mainly attributable to the dehydroxylation of the brucite-like octahedral layers in MgAl-LDH. The fourth stage 4, happened at 486–675 °C with mass loss of 37.45–52.21%, was most probably due to the elimination of NO3 intercalated in the MgAl-LDH interlayers [27]. This thermal decomposition of MgAl-LDH is similar to that of the reported MgAl–NO3 LDH [27]. There were similar mass loss steps for MgAl-Tb-LDH-1 and MgAl-LDH. Four stages were also found for the decomposition of MgAl-Tb-LDH-1. The first stage happened at 25–145 °C, with mass loss of 9.20%, was corresponding to the loss of the adsorbed water and the interlayer water. The second and third stages took place at 145–270 °C and 270–380 °C,
Fig. 4. TG–DTA–DTG curves of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-TbLDH-2, (d) MgAl-Tb-LDH-3, and (e) MgA-Tb-LDH-4.
Table 3 Mass loss steps of all samples.
Fig. 3. IR-FT spectroscopy of MgAl-LDH and MgAl-Tb-LDH-n (n¼ 1,2,3,4).
Samples
Stage1 (weight loss/%)
Stage 2
Stage 3
MgAl-LDH MgAl-Tb-LDH-1 MgAl-Tb-LDH-2 MgAl-Tb-LDH-3 MgAl-Tb-LDH-4
25–145 °C 25–145 °C 25–145 °C 25–145 °C 25–145 °C
145–320 °C 145–270 °C 145–340 °C 145–410 °C 145–360 °C
320–486 °C 486–640 °C 270–380 °C 380–628 °C 340–550 °C 410–600 °C 360–550 °C
(10.46%) (9.20%) (9.20%) (9.98%) (10.20%)
Stage 4
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Fig. 5. Excitation spectra of MgAl-Tb-LDH-n (n ¼1,2,3,4).
respectively, were attributed to the dehydroxylation of the brucitelike octahedral layers. The fourth stage at 380–628 °C was mainly due to the elimination of interlayer NO3 . By contrast, only three stages were obviously observed from the TG–DTG curves of MgAlTb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4. The first stage emerged in 25–145 °C for the three samples, with mass losses of 9.20%, 9.98%, and 10.20%, respectively, was attributed to the evaporation of physically adsorbed and interlayer water. The second stage happened at 145–340 °C, 145–410 °C, and 145–360 °C, respectively, mainly due to the dehydroxylation of LDH layers. The third stage appeared in 340–550, 410–600, and 360–50 °C, respectively, for the three samples, which are owing to the elimination of interlayer NO3 . The decomposing stages of the MgAlTb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4 are different from those of the MgAl-LDH and MgAl-Tb-LDH-1, which may be attributed to the different crystallinity, Mg2 þ /(Al3 þ þTb3 þ ) molar ratio, or the different interlayer water content of the samples. 3.3. Fluorescence Fig. 5 displays excitation spectra of MgAl-Tb-LDH-n (n ¼1,2,3,4). The excitation spectra were obtained at an emission wavelength of 544 nm, which corresponds to the 5D4-7F5 transition emission of Tb(III). Some strong excitation bands appeared at 350, 370, and 380 nm, assigned to 7F6-5G4, 7F6-5L10, and 7F6-5G6 electronic transitions, respectively [34,43]. Meanwhile, some weak excitation bands emerged at 274, 285, 320, 340, and 486 nm. The band at 274–285 nm was attributed to the 4f 8- 4f75d1 Tb transition [44,45]; while the bands at 320–340 and 486 nm may be due to 5 D2’7F6 and 5D4’7F6, respectively [34,46]. According to the excitation spectra of samples, emission spectra recorded at room temperature for all the samples were in optimum excitation with 350 and 380 nm wavelength (shown in Fig. 6). The emission spectra of Tb (OH)3 show a abroad peak at 475–494 nm. No discrete emissions due to the transitions of 5 D4-7FJ (J ¼3, 4, 5, 6) were observed, which was similar to the literatures [47–50]. The emission spectrum of MgAl-LDH also exhibited a broad band at 450–475 nm, which may be due to energy gap of MgAl-LDH. While Tb3 þ ions were incorporated into layers of MgAl-LDHs, the emission spectra of all the Tb-doped LDHs exhibited typical emissions attributed to 5D4-7FJ ( J ¼3, 4, 5, 6) transitions of Tb3 þ , corresponding to 623, 586, 544, and 490 nm, respectively. These green emissions (490 and 544 nm) are as strong as those of organic Tb-complexes [51–55]. The emission spectra are dominated by the peak at around 544 m ascribed to
Fig. 6. Fluorescent spectra of Tb(OH)3 and MgAl-Tb-LDH-n (n¼1,2,3,4) under excitation of 350 and 380 nm wavelengths.
the 5D4-7F5 transition of Tb3 þ . This electric-dipole allowed transition is hypersensitive, so its intensity is strongly dependent on the Tb3 þ surrounding, and it always will be dominant when Tb3 þ is in the lattice site of noncentro-symmetric environment in the cube-like phases [56–59]. The 5D4-7F6 transition however has a magnetic dipole character and its intensity is almost independent of the environment. In this way, the ratio of the (5D4-7F5)/ (5D4-7F6) emission intensity can give us valuable information about the symmetry of the site in which Tb3 þ ions are situated [55]. It was found the decreases in ratio of the (5D4-7F5)/ (5D4-7F6) emission intensity with increasing molar ratio of Mg2 þ / (Al3 þ þ Tb3 þ ) from 1.0 to 4.0 (seen in Fig. 7), indicating that the Tb3 þ surroundings in these samples are different and present an
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Fig. 7. Ratio of (5D4–7F5)/(5D4–7F6) emission intensity depending on molar ratio of Mg2 þ (Al3 þ þ Tb3 þ ).
increase in the symmetry of the Tb3 þ site with increasing molar ratio of Mg2 þ /(Al3 þ þ Tb3 þ ) from 1.0 to 4.0. The highest value for the sample with Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratio of 1.0 suggested distorted local environment for the Tb3 þ ion. The lowest value for the sample with Mg2 þ /(Al3 þ þTb3 þ ) molar ratio of 4.0, corresponded to less distorted local environment for the Tb3 þ ion. The ratio of the (5D4-7F5)/(5D4-7F6) emission intensity tended to decrease when the molar ratio of Mg2 þ /(Al3 þ þ Tb3 þ ) varied from 1.0 to 4.0, indicating the less lattice distortion in the local environment of the Tb3 þ ion, due to less divalent metal ions (Mg2 þ ) isomorphously substituted by trivalent metal ions (Al3 þ þTb3 þ ) in the LDH framework. This result was in accordant to the previous work [24].
4. Conclusions Tb-doped Mg–Al layered double hydroxides (LDHs) with various Mg2 þ /(Al3 þ þTb3 þ ) molar ratios from 1.0 to 4.0 were synthesized by the co-precipitation at room temperature. The XRD patterns confirmed the incorporation of Tb3 þ ions onto layers of MgAl-LDHs and presented a single phase. The effect of Mg2 þ / (Al3 þ þ Tb3 þ ) molar ratios on the crystallinity of the hydrotalcite materials indicated that the increase in the Mg2 þ /(Al3 þ þTb3 þ ) molar ratios favored the formation of the hydrotalcite. Fluorescent spectra showed that all the Tb-doped MgAl-LDHs exhibited strong green emissions compared with that of Tb(OH)3 as well as those of reported Tb(III) organic complex. This result suggested that the MgAl-NO3-LDHs system was favorable for the emissions of Tb3 þ ions, which is important as a fluorescent probe for the Tb-doped MgAl-LDHs to be application in biological technology in the future.
Acknowledgments The Project was supported by National Natural Science Foundation of China (No. 51162021).
References [1] S. Petoud, G. Muller, E.G. Moore, J. Xu, J. Sokolnicki, J.P. Riehl, U.N. Le, S.M. Cohen, K.N. Raymond, J. Am. Chem. Soc. 129 (2007) 77. [2] J. Xu, T.M. Corneillie, E.G. Moore, G.L. Law, N.G. Butlin, K.N. Raymond, J. Am. Chem. Soc. 133 (2011) 19900. [3] D. Zhang, Y. Lu, D. Zhu, Y. Xu, Inorg. Chem. 52 (2013) 3253. [4] J. Han, L. Wang, S.S. Wong, J. Phys. Chem. C 118 (2014) 5671.
[5] J.A. Dorman, J.H. Choi, G. Kuzmanich, J.P. Chan, J. Phys. Chem. C 116 (2012) 12854. [6] G.A. Sotiriou, M. Schneider, S.E. Pratsinis, J. Phys. Chem. C 115 (2011) 1084. [7] B.K. McMahon, T. Gunnlaugsson, J. Am. Chem. Soc. 134 (2012) 10725. [8] X.P. Yang, R.A. Jones, J. Am. Chem. Soc. 127 (2005) 7686. [9] A.P.S. Samuel, J. Xu, K.N. Raymond, Inorg. Chem. 48 (2009) 687. [10] C.J. Gao, A.M. Kirillov, W. Dou, X.L. Tang, L.L. Liu, X.H. Yan, Y.J. Xie, P.X. Zang, W.S. Liu, Y. Tang, Inorg. Chem. 53 (2014) 935. [11] S. Viswanathan, A. Bettencourt-Dias, Inorg. Chem. 45 (2006) 10138. [12] H.B. Xiao, M.J. Chen, C. Mei, H.Y. Yin, X.Y. Zhang, X.X. Cao, Spectrochim. Acta Part A 84 (2011) 238. [13] B. Yue, Y.N. Chen, H.B. Chu, Y.R. Qu, A.L. Wang, Y.L. Zhao, Inorg. Chim. Acta 414 (2014) 39. [14] J.Q. Bao, Z.F. Zhang, R.R. Tang, H.X. Han, Z.F. Yang, J. Lumin. 136 (2013) 68. [15] N.E. Greig, J.D. Einkauf, J.M. Clark, E.J. Corcoran, J.P. Karrama, C.A. Kent, V.E. Eugene, B.C. Chan, D.T. deLill, J. Solid State Chem. 225 (2015) 402. [16] L. Zhang, Y.F. Jia, X.B. Xu, Z.L. Liu, J.K. Tang, J. Lumin. 132 (2012) 1906. [17] W.T. Chen, R.H. Hu, Y.F. Wang, X. Zhang, J. Liu, J. Solid State Chem. 213 (2014) 218. [18] Y. Yang, Y.Q. Zhang, G.B. Shu, Q. Dong, L.L. Zou, Y.G. Zhu, J. Lumin. 159 (2015) 73. [19] J.V. Soares, C.F. Gugliotti, Y.S. Kawashima, S.H. Tatumi, J.C.R. Mittani, Radiat. Meas. 5 (2014) 15. [20] Y.S. Kawashima, C.F. Gugliotti, M. Yee, S.H. Tatumi, J.C.R. Mittani, Radiat. Phys. Chem. 95 (2014) 91. [21] N.G. Zhuravleva, A.A. Eliseev, A.V. Lukashin, U. Kynast, Y.D. Tretyakov, Mendeleev Commun. 14 (2004) 176. [22] L.L. Liu, Q. Wang, D. Xia, T.T. Shen, M.H. Yu, W.S. Liu, Y. Tang, Chin. Chem. Lett. 24 (2013) 93. [23] Y.F. Chen, S.H. Zhou, F. Li, Y.W. Chen, J. Mater. Sci. 45 (2010) 6417. [24] Y.F. Chen, F. Li, S.H. Zhou, J.C. Wei, Y.F. Dai, Y.W. Chen, J. Solid State Chem. 183 (2010) 2222. [25] P. Vialat, F. Leroux, C. Taviot-Gueho, G. Villemure, C. Mousty, Electrochim. Acta 107 (2013) 599. [26] X.B. Wang, Z.M. Bai, D. Zhao, Y.P. Chai, M. Guo, J.Y. Zhang, Mater. Res. Bull. 48 (2013) 1228. [27] T. Kameda, Y. Fubasami, N. Uchiyama, T. Yoshioka, Thermochim. Acta 499 (2010) 106. [28] L.J. Wang, X.Y. Xu, D.G. Evans, X. Duan, D.Q. Li, J. Solid State Chem. 183 (2010) 1114. [29] Y. Zhang, L.Q. Wang, L.J. Zou, D.F. Xue, J. Cryst. Growth 312 (2010) 3367. [30] M. Dadwhal, M. Sahimi, T.T. Tsotsis, Ind. Eng. Chem. Res. 50 (2011) 2220. [31] M.J. Reis, F. Silvério, J. Tronto, J.B. Valim, J. Phys. Chem. Solids 65 (2004) 487. [32] J.G. Wang, Y. Wei, J. Yu, Appl. Clay Sci. 72 (2013) 37. [33] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173. [34] Y. Sohn, Ceram. Int. 40 (2014) 13803. [35] N. Iyi, T. Sasaki, J. Colloid Interface Sci. 322 (2008) 237. [36] N. Iyi, T. Sasaki, Appl. Clay Sci. 42 (2008) 246. [37] M. Zhang, B. Gao, Y. Yao, M. Inyang, Chemosphere 92 (2013) 1042. [38] K. Vivekanandan, S. Selvasekarapandian, P. Kolandaivel, Mater. Chem. Phys. 39 (1995) 284. [39] P.V. Jentzsch, V. Ciobota, R.M. Bolanz, B. Kampe, P. Rosch, J. Majzlan, J. Popp, J. Mol. Struct. 1022 (2012) 147. [40] F.P. de Sá, B.N. Cunha, L.M. Nunes, Chem. Eng. J. 215/216 (2013) 122. [41] X.B. Wang, Z.M. Bai, D. Zhao, Y.P. Chai, M. Guo, J.Y. Zhang, Mater. Res. Bull. 48 (2013) 1228. [42] R.R. Delgado, C.P.D. Pauli, C.B. Carrasco, M.J. Avena, Appl. Clay Sci. 40 (2008) 27. [43] P.V. Jyothy, K.A. Amrutha, J. Gijo, N.V. Unnikrishnan, J. Fluoresc. 19 (2009) 165. [44] R. Reisfeld, M. Zelner, A. Patra, J. Alloy. Compd. 300/301 (2000) 147. [45] A.A. Ismail, M. Abboudi, P. Holloway, H. El-Shall, Mater. Res. Bull. 42 (2007) 137. [46] C. Davesnne, A. Ziani, C. Labbé, P. Marie, C. Frilay, X. Portier, Thin Solid Films 553 (2014) 33.
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[47] J. Domaradzki, E.L. Prociow, D. Kaczmarek, A. Borkowska, T. Berlicki, K. Prociow, Opt. Mater. 31 (2009) 1349. [48] M. Ayvackl, A. Canimoglu, Y. Karabulut, Z. Kotan, L.K.S. Herval, M.P.F. de Godoy, Y.G. Gobato, M. Henini, N. Can, J. Alloy. Compd. 590 (2014) 417. [49] P.P. Pal, J. Manam, Mater. Sci. Eng. B 178 (2013) 400. [50] G.L. Kabongo, G.H. Mhlongo, T. Malwela, B.M. Mothudi, K.T. Hillie, M.S. Dhlamini, J. Alloy. Compd. 591 (2014) 156. [51] Z.Q. Xia, Q. Wei, S.P. Chen, X.M. Feng, G. Xie, C.F. Qiao, G.C. Zhang, S.L. Gao, J. Solid State Chem. 197 (2013) 489. [52] J.T. Lin, Y.H. Zheng, Q.M. Wang, Dyes Pigments 112 (2015) 239. [53] E.C. Spencer, J. Zhao, N.L. Ross, M.B. Andrews, R.G. Surbella, C.L. Cahill, J. Solid State Chem. 202 (2013) 99.
77
[54] M. Khorasani-Motlagh, M. Noroozifar, S. Niroomand, A. Moodi, J. Lumin. 143 (2013) 56. [55] N. Hildebrandt, K.D. Wegner, W.R. Algar, Coord. Chem. Rev. 273–274 (2014) 125. [56] Y. Liu, Z. Yang, Mater. Lett. 65 (2011) 1853. [57] A.P.A. Marques, F.V. Motta, M.A. Cruz, J.A. Varela, E. Longo, I.L.V. Rosa, Solid State Ion. 202 (2011) 54. [58] Z. Li, J. Zeng, C. Chen, Y. Li, J. Cryst. Growth 286 (2006) 487. [59] F.V. Motta, A.P.A. Marques, M.S. Li, M.F.C. Abreu, C.A. Paskocimas, M.R. D. Bomio, R.P. Souza, J.A. Varela, E. Longo, J. Alloy. Compd. 553 (2013) 338.
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Full Length Article
Excellent green emission of Tb3 þ incorporated in MgAl–NO3 layered double hydroxides system Yufeng Chen n, Yao Bao, Zhipeng Yu, Guangchao Yang, Ling Zhang College of Chemistry, Nanchang University, Nanchang 330031, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 August 2015 Received in revised form 26 August 2016 Accepted 27 August 2016 Available online 31 August 2016
A series of Tb-doped MgAl–NO3 layered double hydroxides (LDHs) with Mg2 þ /(Al3 þ þTb3 þ ) molar ratios ranging from 1.0 to 4.0 were synthesized through co-precipitation method at room temperature. X-ray diffraction (XRD) results indicated that the crystallinity of all the Tb-doped samples presented a single phase corresponding to LDHs. SEM measurement suggested that all the samples have similar morphologies. Fluorescence spectra show strong green emissions at 490 and 544 nm, ascribed to the 5 D4-7F6 and 5D4-7F5 transition of Tb3 þ , respectively. This result revealed that the MgAl–NO3 LDH system was favorable for the green emissions of Tb3 þ ions. & 2016 Elsevier B.V. All rights reserved.
Keywords: MgAl-LDHs Tb3 þ -doped Co-precipitation method Fluorescence
1. Introduction Rare-earth doped materials, such as nanocrystals or organic complexes, have been extensive studies owing to their luminescence properties [1–6]. In particular, Eu(III) and Tb(III) complexes have attracted attention due to their well-defined luminescence properties, including hypersensitivity to the coordination environment, and narrow bandwidth [7–11]. In comparison with that of trivalent europium ion, the study on luminescent property of trivalent terbium ion is limited. Moreover, most studies on the fluorescence of trivalent terbium ions focus on its organic complexes [12–18], and reveal the energy transfer from organic ligand to Tb (III) occurred in the Tb (III) complexes [16,18]. In view of the thermal and chemical stability as well as less environmental pollution, the investigation about Tb (III) doped inorganic materials is still worthwhile to be paid attention. Despite some reports on the studies of Tb-doped inorganic materials, the preparation of materials related to sintering process at high temperature is in need of much energy consumption [19,20]. Therefore, it is important to prepare the Tb-doped inorganic materials at room temperatures, especially for inorganic layered double hydroxides that are potential application in biological technology. However, some studies on Tb-complex ions intercalated into layered double hydroxides were developed. For example, Zhuravleva et al. have investigated the luminescent hybrid materials based on mixed Eu/Tb n
Corresponding author. Fax: þ 86 791 3969514. E-mail address: [email protected] (Y. Chen).
http://dx.doi.org/10.1016/j.jlumin.2016.08.060 0022-2313/& 2016 Elsevier B.V. All rights reserved.
complexes intercalated into Mg–Al LDH [21], and revealed highly efficient ligand-Tb3 þ /Eu3 þ and Tb3 þ -Eu3 þ communication channels; Liu et al. have studied the intercalation of organic sensitizer guests into layered Tb(OH)3, and found synergistic effects in luminescence enhancing and tuning [22]. In order to better apply the fluorescence of Tb3 þ to biological technology, along with our successful experiences of Eu ion doped onto layers of LDHs [23,24], we have further incorporated Tb3 þ onto the brucite-like octahedral layers of MgAl-LDH, and found strong green emission of the Tb3 þ doped into layers of MgAl-LDH. This Tb incorporated onto the layers of LDHs is more favorable for touching outside environment compared with the Tb incorporated into interlayer space of LDHs, which is very important as a fluorescent probe for the potential application in biological technology. The Tb-doped layered double hydroxides should more high thermal stability and less toxicity compared with those Tb–organic complexes.
2. Experimental 2.1. Samples preparation Mg(NO3)2 6H2O, Al(NO3)3 9H2O, Tb2O3, NH3 H2O, and HNO3 were of A.R. grade, and were purchased from Chemistry Reagent Corporation of National Medicine Group. Tb(NO3)3 solution (0.05 mol L 1) was prepared by Tb2O3 solid dissolved in mixed solution of HNO3 and H2O2. In order to keep a constant Tb/(Al þTb) ratio of 0.06, but vary the Mg/(Al þTb) ratio, the amount of Mg (NO3)2 and Al(NO3)3 was adjusted for each sample. That is, a mixed
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solution with the Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratios of 1.0, 2.0, 3.0, and 4.0, and an constant Tb3 þ /(Al3 þ þ Tb3 þ ) molar ratio of 0.06, was obtained by dissolving Mg(NO3)2 6H2O and Al(NO3)3 9H2O solid in dilute HNO3 and joining Tb(NO3)3 solution. Then, a series of Tb-doped MgAl–NO3 layered double hydroxides precipitate produced by the addition of a 3.0 mol L 1 NH3 solution. After precipitation (pH ¼8–9), the suspension aged at 40 °C for two hours, then the slurry was filtrated, washed with deionize water, and dried at 70 °C for 24 h. The MgAl–NO3 samples with Mg2 þ /(Al3 þ þTb3 þ ) molar ratios of 1.0, 2.0, 3.0, and 4.0 were signed as MgAl-Tb-LDH-1, MgAl-Tb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4, respectively. A binary MgAl-LDH with Mg2 þ /Al3 þ molar ratio of 2.0 was prepared by the same method as above. Tb (OH)3 was prepared with above Tb(NO)3 solution (0.05 mol L 1) and NH3 solution (3.0 mol L 1) by precipitation. In order to avoid carbonate contamination, the CO2-free deionized water was used in all the experiments.
range of errors. These results are similar to those of literatures [25–27]. The XRD patterns of synthesized Mg-Al-Tb-LDHs and Tb(OH)3 are shown in Fig. 1. All the samples exhibit a low crystallinity in view of the synthesis conditions (at room temperature, fast addition, aged for 2 h at 40 °C). For the Mg-Al-Tb-LDHs, the main diffraction peaks are in good agreement with the characteristics of hexagonal phase [26]. The position of the first 00l diffraction line situated in the low angle region (2θ) is relevant to the interlayer distance (d) and mainly depends on the size of the intercalated anion. The interlayer distances (d003 ¼9.07–8.81 Å) of all samples are consistent with the presence of NO3 intercalated anions [27,28] (Table 2), but are larger than those of MgAl–CO3 LDHs in
2.2. Characterization techniques Chemical contents of Mg, Al, and Tb were determined by inductively coupled plasma atomic emission spectroscopy (ICPAES Optima 5300DV American Pe Company, America). Scanning electron microscope (SEM, JEOL JSM-6701F, JEOL Company, Akishima, Tokyo, Japan) was employed for the morphology analysis of all the samples. X-ray diffraction (XRD) patterns were performed by a X-ray diffractometer using CuKα radiation (XD-3, Beijing Puxi Tongyong Yiqi Ltd. China). All the samples were scanned in the 2θ range of 4–70° at a scan rate 2°/min. Fourier transform infrared (FTIR) spectra of the solid materials were obtained with Shimadzu IR Prestige-21 FTIR spectrometer by the KBr method. Thermogravimetric (TG) and differential thermogravimetric (DTG) data were collected using synchronous thermal analyzer (PYRIS DIAMOVD, AMERICAN PE COMPANY) under a flowing nitrogen atmosphere at a scan rate of 10 °C/min. The fluorescence of the samples was investigated with the help of F-7000 FL Spectrophotometer.
3. Results and discussion 3.1. Structural and compositional analysis A series of three intra-layer cations LDH incorporating small Tb3 þ by substitution of Al3 þ in a MgAl–NO3 LDHs phase were synthesized by the co-precipitation route at room temperature. The Tb3 þ /(Al3 þ þTb3 þ ) molar ratio was maintained constant at 0.06. From ICP-AES elemental analysis, chemical composition of the as-prepared samples agreed well with those expected based on the composition of the reaction mixtures (Table 1). It is worth noting that although the Mg2 þ /(Al3 þ þTb3 þ ) molar ratio determined from ICP-AES analysis differs from the initial Mg2 þ / (Al3 þ þ Tb3 þ ) molar ratio, the difference is within the reasonable Fig. 1. XRD patterns of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-Tb-LDH-2, (d) MgAl-Tb-LDH-3, (e) MgA-Tb-LDH-4, and (f) Tb(OH)3.
Table 1 Chemical composition of samples by ICP-AES. Samples
MgAl-LDH MgAl-Tb-LDH-1 MgAl-Tb-LDH-2 MgAl-Tb-LDH-3 MgAl-Tb-LDH-4
Mg(Al þ Tb) molar ratio
Tb/(Al þTb) molar ratio
Initial
Experimental
Initial
Experimental
2.00 1.0 2.00 3.00 4.00
1.98 1.01 2.01 2.97 3.96
0.06 0.06 0.06 0.06 0.06
0.06 0.06 0.06 0.06 0.06
Table 2 Lattice parameters of all MgAl-LDH and MgAl-Tb-LDH-n (n¼1,2,3,4). Lattice parameters
MgAl-LDH
Tb-LDH-1
Tb-LDH-2
Tb-LDH-3
Tb-LDH-4
a c
3.202(3) 27.08(9)
3.207(4) 26.99(2)
3.200(1) 26.968(8)
3.199(4) 26.51(6)
3.253(3) 26.57(6)
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Fig. 2. SEM images of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-Tb-LDH-2, (d) MgAl-Tb-LDH-3, and (e) MgAl-Tb-LDH-4.
consideration of the different ionic Radii of NO3 (2.3 Å) and CO32 (1.74 Å) [29–32]. The (0 0 3), (0 0 6) and (0 0 9) peaks of all samples appeared at about 10.2°, 20.1°, and 35.0° respectively. The (1 1 0) peaks of all samples, which represent layer structure, appeared at about 61.7°. Cell parameters c and a, which reflect the interlayer and cation-cation distances, were calculated from the 003 and 110 peak positions, assuming 3R stacking [25,33]. The basal distances of d (0 0 3) for all samples are 9.03–8.81 Å and those of d (1 1 0) are 1.50–1.52 Å. The value of the cell parameter a is about two times of the d110 (seen in Table 2) for all the Mg-AlTb-LDHs, which is in agreement with those of previous reports [25,33]. With regard to the Tb(OH)3, the major peaks assigned to (1 0 0), (1 0 1), (0 0 2), and (2 2 0) planes of the hexagonal crystal structure were found (JCPDS 01-083-2038). Meanwhile, an undefined impurity peak (assigned as *) appeared. This impurity peak was also observed in the Tb(OH)3 phase prepared by Sohn [34]. In the light of the diffraction intensity of XRD, the crystallinity of the Tb-doped LDH tended to be better while the Mg2 þ / (Al3 þ þTb3 þ ) molar ratio varied from 1.0 to 4.0. No phase corresponding to Tb(OH)3 (Fig. 1(f)) [34] or other Tb3 þ -contained compounds was observed. This indicated that the Tb3 þ ions should be isomorphously present in the brucite-like layer because of their favorable ionic radii (Tb3 þ 0.92 Å, Al3 þ 0.51 Å, and
Mg2 þ 0.66 Å). The crystallographic parameters of the ternary MgAl-Tb-LDHs and binary MgAl-LDH were refined basing on the XRD data (seen in Table 2) and literatures [28,29]. Small differences appeared in all samples. In general, the parameter c can be affected by various factors such as the amount of interlayer water and anions, Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratio, and the crystallinity of the samples, etc. It is very complicated to define these influencing factors. It is noteworthy that the SEM images (seen in Fig. 2) of all the samples are neither the hexagonal platelike synthesized by hydrothermal reaction [26,29,35,36] nor other morphologies reported [37], but similar to the previous MgAl–NO3 [28]. These morphological differences may be due to different preparing conditions or processes. Meanwhile, FT-IR spectroscopy (Fig. 3) shows a strong sharp band at 1386 cm 1 attributed to stretching vibrations of NO3 ions [38–40], a broad strong band at 3445 cm 1 along with a weak sharp band at 1642 cm 1 ascribed to O–H stretching and bending modes from layer and the interlayer water molecules [41]. The bands at 654 and 444 cm 1 are due to metal–oxygen vibration [24,42]. All these results indicated the formation of the Tb-doped MgAl–NO3 LDHs. It was worthwhile to notice that the bands at 2973 and 1049 cm 1 only appeared in the MgAl-Tb-LDH-3, but were not found in other MgAl-Tb-LDHs.
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The reason is that the bands at 2973 and 1049 cm 1 are attributed to ethanol which is used as a cleaning agent during measurement. 3.2. Thermogravimetry and differential thermogravimetry (TG–DTG) Fig. 4 shows the TG and differential thermal gravimetry (DTG) curves obtained for all the samples, and the corresponding mass loss stages present in Table 3. The decomposition of MgAl-LDH occurred in the following four stages: stage 1, mass loss of 0–10.46% until 145 °C, corresponded to the evaporation of surface adsorbed water and interlayer water in MgAl-LDH; stage 2, mass loss of 10.46–19.71% at 145–320 °C; stage 3, mass loss of 19.71– 37.45% at 320–486 °C. The second and third stages were mainly attributable to the dehydroxylation of the brucite-like octahedral layers in MgAl-LDH. The fourth stage 4, happened at 486–675 °C with mass loss of 37.45–52.21%, was most probably due to the elimination of NO3 intercalated in the MgAl-LDH interlayers [27]. This thermal decomposition of MgAl-LDH is similar to that of the reported MgAl–NO3 LDH [27]. There were similar mass loss steps for MgAl-Tb-LDH-1 and MgAl-LDH. Four stages were also found for the decomposition of MgAl-Tb-LDH-1. The first stage happened at 25–145 °C, with mass loss of 9.20%, was corresponding to the loss of the adsorbed water and the interlayer water. The second and third stages took place at 145–270 °C and 270–380 °C,
Fig. 4. TG–DTA–DTG curves of (a) MgAl-LDH, (b) MgAl-Tb-LDH-1, (c) MgAl-TbLDH-2, (d) MgAl-Tb-LDH-3, and (e) MgA-Tb-LDH-4.
Table 3 Mass loss steps of all samples.
Fig. 3. IR-FT spectroscopy of MgAl-LDH and MgAl-Tb-LDH-n (n¼ 1,2,3,4).
Samples
Stage1 (weight loss/%)
Stage 2
Stage 3
MgAl-LDH MgAl-Tb-LDH-1 MgAl-Tb-LDH-2 MgAl-Tb-LDH-3 MgAl-Tb-LDH-4
25–145 °C 25–145 °C 25–145 °C 25–145 °C 25–145 °C
145–320 °C 145–270 °C 145–340 °C 145–410 °C 145–360 °C
320–486 °C 486–640 °C 270–380 °C 380–628 °C 340–550 °C 410–600 °C 360–550 °C
(10.46%) (9.20%) (9.20%) (9.98%) (10.20%)
Stage 4
Y. Chen et al. / Journal of Luminescence 181 (2017) 71–77
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Fig. 5. Excitation spectra of MgAl-Tb-LDH-n (n ¼1,2,3,4).
respectively, were attributed to the dehydroxylation of the brucitelike octahedral layers. The fourth stage at 380–628 °C was mainly due to the elimination of interlayer NO3 . By contrast, only three stages were obviously observed from the TG–DTG curves of MgAlTb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4. The first stage emerged in 25–145 °C for the three samples, with mass losses of 9.20%, 9.98%, and 10.20%, respectively, was attributed to the evaporation of physically adsorbed and interlayer water. The second stage happened at 145–340 °C, 145–410 °C, and 145–360 °C, respectively, mainly due to the dehydroxylation of LDH layers. The third stage appeared in 340–550, 410–600, and 360–50 °C, respectively, for the three samples, which are owing to the elimination of interlayer NO3 . The decomposing stages of the MgAlTb-LDH-2, MgAl-Tb-LDH-3, and MgAl-Tb-LDH-4 are different from those of the MgAl-LDH and MgAl-Tb-LDH-1, which may be attributed to the different crystallinity, Mg2 þ /(Al3 þ þTb3 þ ) molar ratio, or the different interlayer water content of the samples. 3.3. Fluorescence Fig. 5 displays excitation spectra of MgAl-Tb-LDH-n (n ¼1,2,3,4). The excitation spectra were obtained at an emission wavelength of 544 nm, which corresponds to the 5D4-7F5 transition emission of Tb(III). Some strong excitation bands appeared at 350, 370, and 380 nm, assigned to 7F6-5G4, 7F6-5L10, and 7F6-5G6 electronic transitions, respectively [34,43]. Meanwhile, some weak excitation bands emerged at 274, 285, 320, 340, and 486 nm. The band at 274–285 nm was attributed to the 4f 8- 4f75d1 Tb transition [44,45]; while the bands at 320–340 and 486 nm may be due to 5 D2’7F6 and 5D4’7F6, respectively [34,46]. According to the excitation spectra of samples, emission spectra recorded at room temperature for all the samples were in optimum excitation with 350 and 380 nm wavelength (shown in Fig. 6). The emission spectra of Tb (OH)3 show a abroad peak at 475–494 nm. No discrete emissions due to the transitions of 5 D4-7FJ (J ¼3, 4, 5, 6) were observed, which was similar to the literatures [47–50]. The emission spectrum of MgAl-LDH also exhibited a broad band at 450–475 nm, which may be due to energy gap of MgAl-LDH. While Tb3 þ ions were incorporated into layers of MgAl-LDHs, the emission spectra of all the Tb-doped LDHs exhibited typical emissions attributed to 5D4-7FJ ( J ¼3, 4, 5, 6) transitions of Tb3 þ , corresponding to 623, 586, 544, and 490 nm, respectively. These green emissions (490 and 544 nm) are as strong as those of organic Tb-complexes [51–55]. The emission spectra are dominated by the peak at around 544 m ascribed to
Fig. 6. Fluorescent spectra of Tb(OH)3 and MgAl-Tb-LDH-n (n¼1,2,3,4) under excitation of 350 and 380 nm wavelengths.
the 5D4-7F5 transition of Tb3 þ . This electric-dipole allowed transition is hypersensitive, so its intensity is strongly dependent on the Tb3 þ surrounding, and it always will be dominant when Tb3 þ is in the lattice site of noncentro-symmetric environment in the cube-like phases [56–59]. The 5D4-7F6 transition however has a magnetic dipole character and its intensity is almost independent of the environment. In this way, the ratio of the (5D4-7F5)/ (5D4-7F6) emission intensity can give us valuable information about the symmetry of the site in which Tb3 þ ions are situated [55]. It was found the decreases in ratio of the (5D4-7F5)/ (5D4-7F6) emission intensity with increasing molar ratio of Mg2 þ / (Al3 þ þ Tb3 þ ) from 1.0 to 4.0 (seen in Fig. 7), indicating that the Tb3 þ surroundings in these samples are different and present an
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Fig. 7. Ratio of (5D4–7F5)/(5D4–7F6) emission intensity depending on molar ratio of Mg2 þ (Al3 þ þ Tb3 þ ).
increase in the symmetry of the Tb3 þ site with increasing molar ratio of Mg2 þ /(Al3 þ þ Tb3 þ ) from 1.0 to 4.0. The highest value for the sample with Mg2 þ /(Al3 þ þ Tb3 þ ) molar ratio of 1.0 suggested distorted local environment for the Tb3 þ ion. The lowest value for the sample with Mg2 þ /(Al3 þ þTb3 þ ) molar ratio of 4.0, corresponded to less distorted local environment for the Tb3 þ ion. The ratio of the (5D4-7F5)/(5D4-7F6) emission intensity tended to decrease when the molar ratio of Mg2 þ /(Al3 þ þ Tb3 þ ) varied from 1.0 to 4.0, indicating the less lattice distortion in the local environment of the Tb3 þ ion, due to less divalent metal ions (Mg2 þ ) isomorphously substituted by trivalent metal ions (Al3 þ þTb3 þ ) in the LDH framework. This result was in accordant to the previous work [24].
4. Conclusions Tb-doped Mg–Al layered double hydroxides (LDHs) with various Mg2 þ /(Al3 þ þTb3 þ ) molar ratios from 1.0 to 4.0 were synthesized by the co-precipitation at room temperature. The XRD patterns confirmed the incorporation of Tb3 þ ions onto layers of MgAl-LDHs and presented a single phase. The effect of Mg2 þ / (Al3 þ þ Tb3 þ ) molar ratios on the crystallinity of the hydrotalcite materials indicated that the increase in the Mg2 þ /(Al3 þ þTb3 þ ) molar ratios favored the formation of the hydrotalcite. Fluorescent spectra showed that all the Tb-doped MgAl-LDHs exhibited strong green emissions compared with that of Tb(OH)3 as well as those of reported Tb(III) organic complex. This result suggested that the MgAl-NO3-LDHs system was favorable for the emissions of Tb3 þ ions, which is important as a fluorescent probe for the Tb-doped MgAl-LDHs to be application in biological technology in the future.
Acknowledgments The Project was supported by National Natural Science Foundation of China (No. 51162021).
References [1] S. Petoud, G. Muller, E.G. Moore, J. Xu, J. Sokolnicki, J.P. Riehl, U.N. Le, S.M. Cohen, K.N. Raymond, J. Am. Chem. Soc. 129 (2007) 77. [2] J. Xu, T.M. Corneillie, E.G. Moore, G.L. Law, N.G. Butlin, K.N. Raymond, J. Am. Chem. Soc. 133 (2011) 19900. [3] D. Zhang, Y. Lu, D. Zhu, Y. Xu, Inorg. Chem. 52 (2013) 3253. [4] J. Han, L. Wang, S.S. Wong, J. Phys. Chem. C 118 (2014) 5671.
[5] J.A. Dorman, J.H. Choi, G. Kuzmanich, J.P. Chan, J. Phys. Chem. C 116 (2012) 12854. [6] G.A. Sotiriou, M. Schneider, S.E. Pratsinis, J. Phys. Chem. C 115 (2011) 1084. [7] B.K. McMahon, T. Gunnlaugsson, J. Am. Chem. Soc. 134 (2012) 10725. [8] X.P. Yang, R.A. Jones, J. Am. Chem. Soc. 127 (2005) 7686. [9] A.P.S. Samuel, J. Xu, K.N. Raymond, Inorg. Chem. 48 (2009) 687. [10] C.J. Gao, A.M. Kirillov, W. Dou, X.L. Tang, L.L. Liu, X.H. Yan, Y.J. Xie, P.X. Zang, W.S. Liu, Y. Tang, Inorg. Chem. 53 (2014) 935. [11] S. Viswanathan, A. Bettencourt-Dias, Inorg. Chem. 45 (2006) 10138. [12] H.B. Xiao, M.J. Chen, C. Mei, H.Y. Yin, X.Y. Zhang, X.X. Cao, Spectrochim. Acta Part A 84 (2011) 238. [13] B. Yue, Y.N. Chen, H.B. Chu, Y.R. Qu, A.L. Wang, Y.L. Zhao, Inorg. Chim. Acta 414 (2014) 39. [14] J.Q. Bao, Z.F. Zhang, R.R. Tang, H.X. Han, Z.F. Yang, J. Lumin. 136 (2013) 68. [15] N.E. Greig, J.D. Einkauf, J.M. Clark, E.J. Corcoran, J.P. Karrama, C.A. Kent, V.E. Eugene, B.C. Chan, D.T. deLill, J. Solid State Chem. 225 (2015) 402. [16] L. Zhang, Y.F. Jia, X.B. Xu, Z.L. Liu, J.K. Tang, J. Lumin. 132 (2012) 1906. [17] W.T. Chen, R.H. Hu, Y.F. Wang, X. Zhang, J. Liu, J. Solid State Chem. 213 (2014) 218. [18] Y. Yang, Y.Q. Zhang, G.B. Shu, Q. Dong, L.L. Zou, Y.G. Zhu, J. Lumin. 159 (2015) 73. [19] J.V. Soares, C.F. Gugliotti, Y.S. Kawashima, S.H. Tatumi, J.C.R. Mittani, Radiat. Meas. 5 (2014) 15. [20] Y.S. Kawashima, C.F. Gugliotti, M. Yee, S.H. Tatumi, J.C.R. Mittani, Radiat. Phys. Chem. 95 (2014) 91. [21] N.G. Zhuravleva, A.A. Eliseev, A.V. Lukashin, U. Kynast, Y.D. Tretyakov, Mendeleev Commun. 14 (2004) 176. [22] L.L. Liu, Q. Wang, D. Xia, T.T. Shen, M.H. Yu, W.S. Liu, Y. Tang, Chin. Chem. Lett. 24 (2013) 93. [23] Y.F. Chen, S.H. Zhou, F. Li, Y.W. Chen, J. Mater. Sci. 45 (2010) 6417. [24] Y.F. Chen, F. Li, S.H. Zhou, J.C. Wei, Y.F. Dai, Y.W. Chen, J. Solid State Chem. 183 (2010) 2222. [25] P. Vialat, F. Leroux, C. Taviot-Gueho, G. Villemure, C. Mousty, Electrochim. Acta 107 (2013) 599. [26] X.B. Wang, Z.M. Bai, D. Zhao, Y.P. Chai, M. Guo, J.Y. Zhang, Mater. Res. Bull. 48 (2013) 1228. [27] T. Kameda, Y. Fubasami, N. Uchiyama, T. Yoshioka, Thermochim. Acta 499 (2010) 106. [28] L.J. Wang, X.Y. Xu, D.G. Evans, X. Duan, D.Q. Li, J. Solid State Chem. 183 (2010) 1114. [29] Y. Zhang, L.Q. Wang, L.J. Zou, D.F. Xue, J. Cryst. Growth 312 (2010) 3367. [30] M. Dadwhal, M. Sahimi, T.T. Tsotsis, Ind. Eng. Chem. Res. 50 (2011) 2220. [31] M.J. Reis, F. Silvério, J. Tronto, J.B. Valim, J. Phys. Chem. Solids 65 (2004) 487. [32] J.G. Wang, Y. Wei, J. Yu, Appl. Clay Sci. 72 (2013) 37. [33] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173. [34] Y. Sohn, Ceram. Int. 40 (2014) 13803. [35] N. Iyi, T. Sasaki, J. Colloid Interface Sci. 322 (2008) 237. [36] N. Iyi, T. Sasaki, Appl. Clay Sci. 42 (2008) 246. [37] M. Zhang, B. Gao, Y. Yao, M. Inyang, Chemosphere 92 (2013) 1042. [38] K. Vivekanandan, S. Selvasekarapandian, P. Kolandaivel, Mater. Chem. Phys. 39 (1995) 284. [39] P.V. Jentzsch, V. Ciobota, R.M. Bolanz, B. Kampe, P. Rosch, J. Majzlan, J. Popp, J. Mol. Struct. 1022 (2012) 147. [40] F.P. de Sá, B.N. Cunha, L.M. Nunes, Chem. Eng. J. 215/216 (2013) 122. [41] X.B. Wang, Z.M. Bai, D. Zhao, Y.P. Chai, M. Guo, J.Y. Zhang, Mater. Res. Bull. 48 (2013) 1228. [42] R.R. Delgado, C.P.D. Pauli, C.B. Carrasco, M.J. Avena, Appl. Clay Sci. 40 (2008) 27. [43] P.V. Jyothy, K.A. Amrutha, J. Gijo, N.V. Unnikrishnan, J. Fluoresc. 19 (2009) 165. [44] R. Reisfeld, M. Zelner, A. Patra, J. Alloy. Compd. 300/301 (2000) 147. [45] A.A. Ismail, M. Abboudi, P. Holloway, H. El-Shall, Mater. Res. Bull. 42 (2007) 137. [46] C. Davesnne, A. Ziani, C. Labbé, P. Marie, C. Frilay, X. Portier, Thin Solid Films 553 (2014) 33.
Y. Chen et al. / Journal of Luminescence 181 (2017) 71–77
[47] J. Domaradzki, E.L. Prociow, D. Kaczmarek, A. Borkowska, T. Berlicki, K. Prociow, Opt. Mater. 31 (2009) 1349. [48] M. Ayvackl, A. Canimoglu, Y. Karabulut, Z. Kotan, L.K.S. Herval, M.P.F. de Godoy, Y.G. Gobato, M. Henini, N. Can, J. Alloy. Compd. 590 (2014) 417. [49] P.P. Pal, J. Manam, Mater. Sci. Eng. B 178 (2013) 400. [50] G.L. Kabongo, G.H. Mhlongo, T. Malwela, B.M. Mothudi, K.T. Hillie, M.S. Dhlamini, J. Alloy. Compd. 591 (2014) 156. [51] Z.Q. Xia, Q. Wei, S.P. Chen, X.M. Feng, G. Xie, C.F. Qiao, G.C. Zhang, S.L. Gao, J. Solid State Chem. 197 (2013) 489. [52] J.T. Lin, Y.H. Zheng, Q.M. Wang, Dyes Pigments 112 (2015) 239. [53] E.C. Spencer, J. Zhao, N.L. Ross, M.B. Andrews, R.G. Surbella, C.L. Cahill, J. Solid State Chem. 202 (2013) 99.
77
[54] M. Khorasani-Motlagh, M. Noroozifar, S. Niroomand, A. Moodi, J. Lumin. 143 (2013) 56. [55] N. Hildebrandt, K.D. Wegner, W.R. Algar, Coord. Chem. Rev. 273–274 (2014) 125. [56] Y. Liu, Z. Yang, Mater. Lett. 65 (2011) 1853. [57] A.P.A. Marques, F.V. Motta, M.A. Cruz, J.A. Varela, E. Longo, I.L.V. Rosa, Solid State Ion. 202 (2011) 54. [58] Z. Li, J. Zeng, C. Chen, Y. Li, J. Cryst. Growth 286 (2006) 487. [59] F.V. Motta, A.P.A. Marques, M.S. Li, M.F.C. Abreu, C.A. Paskocimas, M.R. D. Bomio, R.P. Souza, J.A. Varela, E. Longo, J. Alloy. Compd. 553 (2013) 338.