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Photoluminescence of nanocrystalline YVO4:TmxDy1−x prepared by a modified Pechini method
Materials Letters 61 (2007) 308 – 311 www.elsevier.com/locate/matlet
Photoluminescence of nanocrystalline YVO4:TmxDy1−x prepared by a modified Pechini method Hongwu Zhang a,⁎, Xiaoyan Fu b , Shuyun Niu b , Gongquan Sun a , Qin Xin a,⁎ a
Dalian Institute of Chemical Physics, CAS, P.O. Box 110, Dalian 116023, PR China b Chemistry Department, Liaoning Normal University, Dalian, 116029, PR China Received 13 November 2005; accepted 9 April 2006 Available online 17 May 2006
Abstract This paper reports the luminescence effects of Tm3+ doped YVO4:Dy nanocrystalline synthesized by a modified Pechini method. The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The relationship between the ratio of Tm3+/Dy3+ and the chromaticity is studied, i.e. Tm3+ ion doping effectively tunes the emission color of YVO4:TmxDy1−x phosphors. The best white light emission was observed with YVO4:1%(Tm0.6Dy0.4). These results indicate that thulium doped YVO4:Dy phosphors are promising white-emitting luminescence materials. © 2006 Elsevier B.V. All rights reserved. Keywords: Optical materials; YVO4:Tm,Dy; Photoluminescence
1. Introduction Oxide phosphors have recently gained much attention because of the higher chemical stability of oxide phosphors relative to that of sulfide. White-light-emitting materials are important phosphors which have been widely applied in lighting lamp. There have been many efforts to develop the white-light-emitting oxide phosphors, such as luminescent materials doped with Dy3+, which have been used as novel white-emitting phosphors by adjusting the blue– yellow ratio [1–3]. Due to the lack of the white fluorescent materials, two or more colors must be combined, i.e., a highenergy emitter (e.g. blue) and a relatively low-energy emitter (e.g. green/yellow), to obtain white light emission [4]. It is well known that Tm3+ ions doped into YVO4 or GdVO4 can exhibit blue emissions with excellent color coordinates [5,6]. In addition, due to the location of Dy3+ at a site (D2d) deviated from an inverse center in the host of YVO4, YVO4:Dy exhibited a strong yellow emission [7,8]. So Tm3+- and Dy3+-codoped YVO4 may be a potential white-emitting phosphor, which has been investigated by few people, to the best of the authors' knowledge.
⁎ Corresponding authors. Tel./fax: +86 411 84379071. E-mail address: [email protected] (H. Zhang). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.095
In addition, for good luminescent characteristics, phosphors must have fine size, narrow size distribution, nonaggregation, and spherical morphology particles [9]. Large phosphor particles are more likely to be prone to poor adhesion to the substrate and loss of coating [8]. In addition, nanoparticles enable a wider variation constant and charge transfer properties than polymer which is advantageous for improved efficiency of polymer light-emitting diodes [10]. Thus, fine particles of white phosphors are essential for white-light-emitting diodes (LEDs). The Pechini sol–gel technique is based on forming a solid polymer resin with cations chelated on it in homogeneous manner, which is a good method for the preparation of nanocrystalline composite oxide materials [11,12]. Hence, in this study, we used a modified Pechini method to prepare thulium doped YVO4:Dy and by adjusting the ratio of Tm3+/Dy3+ we realize a white light emission with excellent color coordinates. 2. Experimental High-purity Y2O3 (99.99%), Tm2O3 (99.99%), Dy2O3 (99.99%) and NH4VO3 were taken as the starting chemicals. (NH4)2-EDTA was used as chelating agent and Citric acid (CA, 99%) was used as polymerization agents. The modified Pechini process used to prepare nanosized Tm, Dy-codoped YVO4 is as follows. Firstly, the stoichiometric
H. Zhang et al. / Materials Letters 61 (2007) 308–311
309
amounts of Y2O3, Tm2O3, Dy2O3 and NH4VO3 were dissolved in dilute HNO3 to prepare the solution. After their dissolution (NH4)2-EDTA was added into the solution in the ratio of 1:1. The prepared solution was stirred continuously to ensure the cations complex completely and convert them to stable complexes. Then Citric acid was added into the mixed solution as a polymerization agent. The final PH was adjusted to 6–7 by using ammonia and the solution became transparent and during the whole process, the system was continuously stirred. Finally, the resulting solution was heated in a water bath at 90 °C for 24 h to prepare the gel. The gel was heated in a laboratory furnace at 300 °C to burn out the organic residues and calcined at higher temperature (800 °C) to obtain nanocrystalline YVO4:TmxDy1−x with different ratios of Tm3+/Dy3+. The total concentration of doping ions (Tm3+ and Dy3+) in the samples was kept constant at 1 mol% and this value was checked by chemical analysis. Spectrofluorometer (JASCO, FP6500) equipped with a 450 W Xe lamp was used for the photoluminescence (PL) measurement at room temperature. The CIE coordinates of these luminescent materials were measured by a PMS-3 spectroscan spectrometer. The UV spectrum was recorded using JASCO, V570 with an integral sphere. The quantum yields were determined by comparing the integrated emission of the colloidal solutions (4 × 10− 4 mol L− 1 YVO4:1%(Tm0.6Dy0.4) solution in ethanol) with the emission from a Rhodamine B solution in ethanol having the same optical density and excited at the same wavelength (320 nm). The diffractometer employed was a Rigaku D/MAX RB X-ray diffractometer using Cu Kα(λ = 1.5418 Å) Cu radiation. Micrographs were recorded using JEM-2000Ex transmission electron microscope under a working voltage of 100 kV. Specimens were prepared by dispersing small amounts of the powder in ethanol. 3. Results and discussion The crystalline phase of the nanosized YVO4:1%(Tm0.6Dy0.4) was determined by X-ray diffraction (Fig. 1). As comparison with standard XRD pattern of bulk YVO4 (JCPDS Card 17-341[13]), it is found that the only crystalline form observed is YVO4 and without any evidence
Fig. 1. XRD of YVO4:1%(Tm0.6Dy0.4) nanocrystalline.
Fig. 2. TEM images of nanocrystalline YVO4:1%(Tm0.6Dy0.4) prepared by the modified Pechini method.
of impurity phase, i.e., Y2O3, V2O5. The mean particle size can be roughly determined about 50 nm from the broadening of the peaks by using the Scherrer formula [14]. The TEM micrograph and the particle size distribution given in Fig. 2 show the morphology and particle size of nanocrystalline YVO4:1%(Tm0.6Dy0.4) prepared by the modified Pechini method. It is possible to observe that the particles are approximately spherical with diameters ranging from 30 to 50 nm. The crystalline size data obtained through TEM and X-ray line broadening are thus in good agreement. The typical absorption spectrum of the nanocrystalline YVO4:1% (Tm0.6Dy0.4) is present in Fig. 3 (dot line). The broad bands, peaking at 266 and 300 nm are attributed to the charge transfer from the oxygen ligands to the central vanadium atom inside the VO3− 4 [7,15,16]. The cause of two excitation peaks existing may be attributed to the different V–O bond which was induced by the distortion of YVO4. The absorption intensity is strong, which indicates that the host absorption in UV region is very efficient. Fig. 3 (solid line) shows the excitation spectra of YVO4:1% (Tm0.6Dy0.4) under different monitored lengths of Tm3+ (λem = 475 nm) and Dy3+ (λem = 575 nm), respectively. The two excitation spectra are similar, which consist of a strong broad excitation band with two peaks, one of which centered at 260 nm and the other at 320 nm. It should be
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H. Zhang et al. / Materials Letters 61 (2007) 308–311
Fig. 3. Excitation spectra and absorption spectrum of YVO4:Tm0.6,Dy0.4 at room temperature.
Fig. 5. The blue-to-yellow intensity ratio vs. Tm3+ concentration of the YVO4: TmxDy1−x.
pointed out that the absorption spectrum (Fig. 3, dot line) fits well with both of the excitation spectra of the host, which illustrates that the host of YVO4 can transfer energy to Dy3+ and Tm3+ efficiently. That is, with excitation monitored at host absorption band around 320 nm, whether Tm3+ or Dy3+ in the host of YVO4 can emit bright light with high efficiency. Fig. 4 shows the emission spectra of YVO4:1%(TmxDy1−x) (x = 0–1.0) as a function of Tm3+ contents (x). Excitated at 320 nm, the main emission peak of YVO4:Tm is located at 475 nm which is assigned to 1G4→3H6 transition [5]. There are two dominant bands in the emission spectrum of YVO4:Dy. The yellow band (575 nm) corresponds to the hypersensitive transition 4F9/2→6H13/2 and the blue band (485 nm) corresponds to the 4 F9/2→6H15/2 transition [7]. Because Dy3+ is located at a site (D2d) deviated from an inverse center in the host of YVO4, the intensity of its yellow emission is stronger than that of its blue emission. As the content of Tm3+ enhances gradually, the intensity of blue emission increases accordingly. When the value of x reaches 0.6, the intensity of yellow emission is nearly equal to that of blue emission, which indicates that the emission color of the samples is conveniently controlled by only changing the ratio of Tm3+/Dy3+. The continuous enhancements of Tm3+ contents make the luminescence materials exhibit blue emission. Fig. 5 shows the intensity ratio of blue emission and yellow emission as a function of Tm3+ ions content and Fig. 6 shows the dependence of CIE
coordinate on the content of Tm3+. From the diagram (Fig. 3), it is noticed that the intensity ratio of blue emission and yellow emission is greatly enhanced by the doping of Tm3+ ions. When the content of Tm3+ ions is 0.6, the B/Y intensity ratio reaches 1.035, which means the intensities of these lines in blue and yellow regions are nearly equal. From Fig. 6, it is clearer to see that the coordinate YVO4:1%(Tm0.6Dy0.4) is (0.3417, 0.3540), very close to the equi-energy white point (x = 0.33, y = 0.33). Then the best white light emission was observed with YVO4:0.01(Tm0.6Dy0.4). At the same time, the quantum yield of YVO4:1%(Tm0.6Dy0.4) arrived at 0.61 under UV excitation. So the phosphor YVO4:1%(Tm0.6Dy0.4) is a promising white-emitting luminescence materials. These results suggest that the white emission can be gained by suitably adjusting the ratio of Tm3+/Dy3+ in the host of YVO4. As reported in previous literatures, both YVO4:Tm and YVO4:Dy exhibit strong emission because of the efficient energy transfer from VO3− 4 to the dopant ions [6–9]. From the excitation and emission spectra, it can be seen that the energy transfer between Tm3+ and Dy3+ doesn't happen, which assure that the two dopants in YVO4 can emit intrinsical light, respectively. Therefore the Tm3+ doping may offset the low blue emission intensity of YVO4:Dy to realize the white light emission and does not decrease the emission intensities of this luminescent materials at the same time.
Fig. 4. The luminescence spectra of YVO4:TmxDy1−x (x = 0–1.0) as a function of Tm3+ contents under excitation of 320 nm at room temperature.
Fig. 6. The dependence of CIE coordinate on the content of Tm3+.
H. Zhang et al. / Materials Letters 61 (2007) 308–311
4. Conclusions In summary, we have successfully prepared Tm- and Dycodoped YVO4 nanocrystalline with high luminance of white light emitting by a modified Pechini method. The TEM photograph demonstrated that the crystalline size of the particles was in the range between 30 and 50 nm. The results of the correlation between the ratio of Tm3+/Dy3+ in the host YVO4 and the chromaticity of nanosized YVO4:TmxDy1−x show that Tm3+ ion doping can tune the emission color of this material and the best white light emission is gained when the content of Tm3+ ions is 0.6. In addition, due to the efficient energy transfer from VO43− to the two dopants Tm3+ and Dy3+, YVO4:Tm0.6, Dy0.4 exhibits a strong white light emission. References [1] Q. Su, Z.W. Pei, L.S. Chi, H.J. Zhang, Z.Y. Zhang, F. Zou, J. Alloys Compd. 192 (1993) 25–27. [2] H. Choi, C.-H. Pyun, S.-J. Kim, J. Lumin. 82 (1999) 25–32. [3] H.B. Liang, Q.H. Zeng, Y. Tao, S.B. Wang, Q. Su, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 98 (2003) 213–219.
311
[4] K.X. Yang, W.B. Gao, J.H. Zhao, J.X. Sun, S.X. Lu, S.Y. Liu, Synth. Met. 132 (2002) 43–47. [5] T. Minami, T. Utsubo, T. Miyata, Y. Suzuki, Thin Solid Films 445 (2003) 377–381. [6] H. Zhang, X. Fu, S. Niu, G. Sun, Q. Xin, Solid State Commun. 132 (2004) 527–531. [7] M. Yu, J. Lin, Z. Wang, J. Fu, S. Wang, H.J. Zhang, Y.C. Han, Chem. Mater. 14 (2002) 2224–2231. [8] A. Newport, J. Silver, A. Vecht, J. Electrochem. Sci. 147 (2000) 3944. [9] L.D. Sun, C. Qian, C.S. Liao, X.L. Wang, C.H. Yan, Solid State Commun. 119 (2001) 393. [10] V. Bliznyuk, B. Ruhstaller, P.J. Brock, U. Scherf, S.A. Carter, Adv. Mater. 11 (1999) 1257. [11] S.A.M. Lima, F.A. Sigoli, M.R. Davolos, M. Jafelicci Jr., J. Alloys Compd. 344 (2002) 280–284. [12] Z.G. Wei, L.D. Sun, C.S. Liao, J.L. Yin, X.C. Jiang, C.H. Yan, J. Phys. Chem., B 106 (2002) 10611. [13] JCPDS Powder Diffraction Data base, Joint Committee on Powder Diffraction Standards, International Center of Diffraction Data, Swarthmore, PA, 1990. [14] B.E. Warren, X-ray Diffraction, Dover Publications Inc., New York, 1990. [15] K. Riwotzki, M. Haase, J. Phys. Chem., B 105 (2001) 12709–12713. [16] A. Huignard, V. Buissette, G. Laurent, T. Gacoin, J.-P. Boilot, Chem. Mater. 14 (2002) 2264–2269.
Photoluminescence of nanocrystalline YVO4:TmxDy1−x prepared by a modified Pechini method Hongwu Zhang a,⁎, Xiaoyan Fu b , Shuyun Niu b , Gongquan Sun a , Qin Xin a,⁎ a
Dalian Institute of Chemical Physics, CAS, P.O. Box 110, Dalian 116023, PR China b Chemistry Department, Liaoning Normal University, Dalian, 116029, PR China Received 13 November 2005; accepted 9 April 2006 Available online 17 May 2006
Abstract This paper reports the luminescence effects of Tm3+ doped YVO4:Dy nanocrystalline synthesized by a modified Pechini method. The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The relationship between the ratio of Tm3+/Dy3+ and the chromaticity is studied, i.e. Tm3+ ion doping effectively tunes the emission color of YVO4:TmxDy1−x phosphors. The best white light emission was observed with YVO4:1%(Tm0.6Dy0.4). These results indicate that thulium doped YVO4:Dy phosphors are promising white-emitting luminescence materials. © 2006 Elsevier B.V. All rights reserved. Keywords: Optical materials; YVO4:Tm,Dy; Photoluminescence
1. Introduction Oxide phosphors have recently gained much attention because of the higher chemical stability of oxide phosphors relative to that of sulfide. White-light-emitting materials are important phosphors which have been widely applied in lighting lamp. There have been many efforts to develop the white-light-emitting oxide phosphors, such as luminescent materials doped with Dy3+, which have been used as novel white-emitting phosphors by adjusting the blue– yellow ratio [1–3]. Due to the lack of the white fluorescent materials, two or more colors must be combined, i.e., a highenergy emitter (e.g. blue) and a relatively low-energy emitter (e.g. green/yellow), to obtain white light emission [4]. It is well known that Tm3+ ions doped into YVO4 or GdVO4 can exhibit blue emissions with excellent color coordinates [5,6]. In addition, due to the location of Dy3+ at a site (D2d) deviated from an inverse center in the host of YVO4, YVO4:Dy exhibited a strong yellow emission [7,8]. So Tm3+- and Dy3+-codoped YVO4 may be a potential white-emitting phosphor, which has been investigated by few people, to the best of the authors' knowledge.
⁎ Corresponding authors. Tel./fax: +86 411 84379071. E-mail address: [email protected] (H. Zhang). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.095
In addition, for good luminescent characteristics, phosphors must have fine size, narrow size distribution, nonaggregation, and spherical morphology particles [9]. Large phosphor particles are more likely to be prone to poor adhesion to the substrate and loss of coating [8]. In addition, nanoparticles enable a wider variation constant and charge transfer properties than polymer which is advantageous for improved efficiency of polymer light-emitting diodes [10]. Thus, fine particles of white phosphors are essential for white-light-emitting diodes (LEDs). The Pechini sol–gel technique is based on forming a solid polymer resin with cations chelated on it in homogeneous manner, which is a good method for the preparation of nanocrystalline composite oxide materials [11,12]. Hence, in this study, we used a modified Pechini method to prepare thulium doped YVO4:Dy and by adjusting the ratio of Tm3+/Dy3+ we realize a white light emission with excellent color coordinates. 2. Experimental High-purity Y2O3 (99.99%), Tm2O3 (99.99%), Dy2O3 (99.99%) and NH4VO3 were taken as the starting chemicals. (NH4)2-EDTA was used as chelating agent and Citric acid (CA, 99%) was used as polymerization agents. The modified Pechini process used to prepare nanosized Tm, Dy-codoped YVO4 is as follows. Firstly, the stoichiometric
H. Zhang et al. / Materials Letters 61 (2007) 308–311
309
amounts of Y2O3, Tm2O3, Dy2O3 and NH4VO3 were dissolved in dilute HNO3 to prepare the solution. After their dissolution (NH4)2-EDTA was added into the solution in the ratio of 1:1. The prepared solution was stirred continuously to ensure the cations complex completely and convert them to stable complexes. Then Citric acid was added into the mixed solution as a polymerization agent. The final PH was adjusted to 6–7 by using ammonia and the solution became transparent and during the whole process, the system was continuously stirred. Finally, the resulting solution was heated in a water bath at 90 °C for 24 h to prepare the gel. The gel was heated in a laboratory furnace at 300 °C to burn out the organic residues and calcined at higher temperature (800 °C) to obtain nanocrystalline YVO4:TmxDy1−x with different ratios of Tm3+/Dy3+. The total concentration of doping ions (Tm3+ and Dy3+) in the samples was kept constant at 1 mol% and this value was checked by chemical analysis. Spectrofluorometer (JASCO, FP6500) equipped with a 450 W Xe lamp was used for the photoluminescence (PL) measurement at room temperature. The CIE coordinates of these luminescent materials were measured by a PMS-3 spectroscan spectrometer. The UV spectrum was recorded using JASCO, V570 with an integral sphere. The quantum yields were determined by comparing the integrated emission of the colloidal solutions (4 × 10− 4 mol L− 1 YVO4:1%(Tm0.6Dy0.4) solution in ethanol) with the emission from a Rhodamine B solution in ethanol having the same optical density and excited at the same wavelength (320 nm). The diffractometer employed was a Rigaku D/MAX RB X-ray diffractometer using Cu Kα(λ = 1.5418 Å) Cu radiation. Micrographs were recorded using JEM-2000Ex transmission electron microscope under a working voltage of 100 kV. Specimens were prepared by dispersing small amounts of the powder in ethanol. 3. Results and discussion The crystalline phase of the nanosized YVO4:1%(Tm0.6Dy0.4) was determined by X-ray diffraction (Fig. 1). As comparison with standard XRD pattern of bulk YVO4 (JCPDS Card 17-341[13]), it is found that the only crystalline form observed is YVO4 and without any evidence
Fig. 1. XRD of YVO4:1%(Tm0.6Dy0.4) nanocrystalline.
Fig. 2. TEM images of nanocrystalline YVO4:1%(Tm0.6Dy0.4) prepared by the modified Pechini method.
of impurity phase, i.e., Y2O3, V2O5. The mean particle size can be roughly determined about 50 nm from the broadening of the peaks by using the Scherrer formula [14]. The TEM micrograph and the particle size distribution given in Fig. 2 show the morphology and particle size of nanocrystalline YVO4:1%(Tm0.6Dy0.4) prepared by the modified Pechini method. It is possible to observe that the particles are approximately spherical with diameters ranging from 30 to 50 nm. The crystalline size data obtained through TEM and X-ray line broadening are thus in good agreement. The typical absorption spectrum of the nanocrystalline YVO4:1% (Tm0.6Dy0.4) is present in Fig. 3 (dot line). The broad bands, peaking at 266 and 300 nm are attributed to the charge transfer from the oxygen ligands to the central vanadium atom inside the VO3− 4 [7,15,16]. The cause of two excitation peaks existing may be attributed to the different V–O bond which was induced by the distortion of YVO4. The absorption intensity is strong, which indicates that the host absorption in UV region is very efficient. Fig. 3 (solid line) shows the excitation spectra of YVO4:1% (Tm0.6Dy0.4) under different monitored lengths of Tm3+ (λem = 475 nm) and Dy3+ (λem = 575 nm), respectively. The two excitation spectra are similar, which consist of a strong broad excitation band with two peaks, one of which centered at 260 nm and the other at 320 nm. It should be
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H. Zhang et al. / Materials Letters 61 (2007) 308–311
Fig. 3. Excitation spectra and absorption spectrum of YVO4:Tm0.6,Dy0.4 at room temperature.
Fig. 5. The blue-to-yellow intensity ratio vs. Tm3+ concentration of the YVO4: TmxDy1−x.
pointed out that the absorption spectrum (Fig. 3, dot line) fits well with both of the excitation spectra of the host, which illustrates that the host of YVO4 can transfer energy to Dy3+ and Tm3+ efficiently. That is, with excitation monitored at host absorption band around 320 nm, whether Tm3+ or Dy3+ in the host of YVO4 can emit bright light with high efficiency. Fig. 4 shows the emission spectra of YVO4:1%(TmxDy1−x) (x = 0–1.0) as a function of Tm3+ contents (x). Excitated at 320 nm, the main emission peak of YVO4:Tm is located at 475 nm which is assigned to 1G4→3H6 transition [5]. There are two dominant bands in the emission spectrum of YVO4:Dy. The yellow band (575 nm) corresponds to the hypersensitive transition 4F9/2→6H13/2 and the blue band (485 nm) corresponds to the 4 F9/2→6H15/2 transition [7]. Because Dy3+ is located at a site (D2d) deviated from an inverse center in the host of YVO4, the intensity of its yellow emission is stronger than that of its blue emission. As the content of Tm3+ enhances gradually, the intensity of blue emission increases accordingly. When the value of x reaches 0.6, the intensity of yellow emission is nearly equal to that of blue emission, which indicates that the emission color of the samples is conveniently controlled by only changing the ratio of Tm3+/Dy3+. The continuous enhancements of Tm3+ contents make the luminescence materials exhibit blue emission. Fig. 5 shows the intensity ratio of blue emission and yellow emission as a function of Tm3+ ions content and Fig. 6 shows the dependence of CIE
coordinate on the content of Tm3+. From the diagram (Fig. 3), it is noticed that the intensity ratio of blue emission and yellow emission is greatly enhanced by the doping of Tm3+ ions. When the content of Tm3+ ions is 0.6, the B/Y intensity ratio reaches 1.035, which means the intensities of these lines in blue and yellow regions are nearly equal. From Fig. 6, it is clearer to see that the coordinate YVO4:1%(Tm0.6Dy0.4) is (0.3417, 0.3540), very close to the equi-energy white point (x = 0.33, y = 0.33). Then the best white light emission was observed with YVO4:0.01(Tm0.6Dy0.4). At the same time, the quantum yield of YVO4:1%(Tm0.6Dy0.4) arrived at 0.61 under UV excitation. So the phosphor YVO4:1%(Tm0.6Dy0.4) is a promising white-emitting luminescence materials. These results suggest that the white emission can be gained by suitably adjusting the ratio of Tm3+/Dy3+ in the host of YVO4. As reported in previous literatures, both YVO4:Tm and YVO4:Dy exhibit strong emission because of the efficient energy transfer from VO3− 4 to the dopant ions [6–9]. From the excitation and emission spectra, it can be seen that the energy transfer between Tm3+ and Dy3+ doesn't happen, which assure that the two dopants in YVO4 can emit intrinsical light, respectively. Therefore the Tm3+ doping may offset the low blue emission intensity of YVO4:Dy to realize the white light emission and does not decrease the emission intensities of this luminescent materials at the same time.
Fig. 4. The luminescence spectra of YVO4:TmxDy1−x (x = 0–1.0) as a function of Tm3+ contents under excitation of 320 nm at room temperature.
Fig. 6. The dependence of CIE coordinate on the content of Tm3+.
H. Zhang et al. / Materials Letters 61 (2007) 308–311
4. Conclusions In summary, we have successfully prepared Tm- and Dycodoped YVO4 nanocrystalline with high luminance of white light emitting by a modified Pechini method. The TEM photograph demonstrated that the crystalline size of the particles was in the range between 30 and 50 nm. The results of the correlation between the ratio of Tm3+/Dy3+ in the host YVO4 and the chromaticity of nanosized YVO4:TmxDy1−x show that Tm3+ ion doping can tune the emission color of this material and the best white light emission is gained when the content of Tm3+ ions is 0.6. In addition, due to the efficient energy transfer from VO43− to the two dopants Tm3+ and Dy3+, YVO4:Tm0.6, Dy0.4 exhibits a strong white light emission. References [1] Q. Su, Z.W. Pei, L.S. Chi, H.J. Zhang, Z.Y. Zhang, F. Zou, J. Alloys Compd. 192 (1993) 25–27. [2] H. Choi, C.-H. Pyun, S.-J. Kim, J. Lumin. 82 (1999) 25–32. [3] H.B. Liang, Q.H. Zeng, Y. Tao, S.B. Wang, Q. Su, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 98 (2003) 213–219.
311
[4] K.X. Yang, W.B. Gao, J.H. Zhao, J.X. Sun, S.X. Lu, S.Y. Liu, Synth. Met. 132 (2002) 43–47. [5] T. Minami, T. Utsubo, T. Miyata, Y. Suzuki, Thin Solid Films 445 (2003) 377–381. [6] H. Zhang, X. Fu, S. Niu, G. Sun, Q. Xin, Solid State Commun. 132 (2004) 527–531. [7] M. Yu, J. Lin, Z. Wang, J. Fu, S. Wang, H.J. Zhang, Y.C. Han, Chem. Mater. 14 (2002) 2224–2231. [8] A. Newport, J. Silver, A. Vecht, J. Electrochem. Sci. 147 (2000) 3944. [9] L.D. Sun, C. Qian, C.S. Liao, X.L. Wang, C.H. Yan, Solid State Commun. 119 (2001) 393. [10] V. Bliznyuk, B. Ruhstaller, P.J. Brock, U. Scherf, S.A. Carter, Adv. Mater. 11 (1999) 1257. [11] S.A.M. Lima, F.A. Sigoli, M.R. Davolos, M. Jafelicci Jr., J. Alloys Compd. 344 (2002) 280–284. [12] Z.G. Wei, L.D. Sun, C.S. Liao, J.L. Yin, X.C. Jiang, C.H. Yan, J. Phys. Chem., B 106 (2002) 10611. [13] JCPDS Powder Diffraction Data base, Joint Committee on Powder Diffraction Standards, International Center of Diffraction Data, Swarthmore, PA, 1990. [14] B.E. Warren, X-ray Diffraction, Dover Publications Inc., New York, 1990. [15] K. Riwotzki, M. Haase, J. Phys. Chem., B 105 (2001) 12709–12713. [16] A. Huignard, V. Buissette, G. Laurent, T. Gacoin, J.-P. Boilot, Chem. Mater. 14 (2002) 2264–2269.