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Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature
Materials Letters 64 (2010) 1235–1237
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature Lin Ma a,1, Yuzeng Sun a,1, Peng Gao b,⁎, Yongkui Yin a,1, Zengming Qin a, Baibin Zhou a,⁎ a b
Key Laboratory of Physical and Chemical Materials, College of Heilongjiang Province, Harbin Normal University, Harbin 150025, PR China Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001, PR China
a r t i c l e
i n f o
Article history: Received 16 January 2010 Accepted 28 February 2010 Available online 6 March 2010 Keywords: Hierarchical Nanostructures Controlled synthesis BaMoO4 BaWO4
a b s t r a c t Controlled synthesis of hierarchical Barium molybdate (BaMoO4) nanostructures with different morphologies, such as peanut-like, cube-like and flower-like, was successfully achieved in aqueous solution at room temperature. The obtained products were characterized by a scanning electron microscope (SEM) and an Xray power diffractometer (XRD). The morphologies of the obtained products were found to be greatly dependent on reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio. This controllable method could be readily extended to produce hierarchical Barium tungstate (BaWO4) nanostructures with peanutlike, dumbbell-like, sphere-like and flower-like morphologies. The photoluminescence (PL) properties of the obtained BaMoO4 and BaWO4 nanostructures exhibited strong dependence on the morphologies and sizes, respectively. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The synthesis of hierarchical nanostructures with controlled shape and size is important due to their novel properties and potential applications in optics, electronics, magnetics and biology [1,2]. Recent progress shows that various hierarchical nanostructures which may involve the oriented attachment mechanism [3] at some stage have been synthesized, including butterfly-like, leave-like, sheet-like and ellipsoid-like CuO [4–6], dendritic Ag, Ag2Se and alpha-Fe2O3 [7–9], flower-like CaMoO4, SrMoO4 and ZnO [10,11], rod-like PbCrO4 [12], plate-like FeWO4 [13], urchin-like and ribbon-like WO3 [14], spindlelike alpha-GaOOH, alpha-Ga2O3 and beta-Ga2O3 [15], and spherical Co1 − xMnxO [16]. Scheelite BaXO4 (X = W, Mo) are important optoelectronic materials due to their abilities to produce strong luminescence [17] and have great potential applications such as in nuclear spin optical hole burning hosts [18], photocatalysts [19], stimulated Raman scattering [20] and all-solid-state lasers [21–23]. Recently, Marques et al. have successfully demonstrated that BaMoO4 is a highly promising candidate for photoluminescent applications [24]. The BaXO4 hierarchical nanostructures with different morphologies, such as layer-like, sheaf-like, corn-like, double-taper-like, scissors-like, fasciculus-like, dumbbell-like, kernel-like, bowknotlike and cauliflower-like and peniform-like BaWO4 [25–31] and penniform-like, flower-like, nest-like, rod-like and shuttle-like
⁎ Corresponding authors. E-mail addresses: [email protected] (B. Zhou), [email protected] (P. Gao). 1 Lin Ma, Yuzeng Sun and Yongkui Yin contributed equally to this work. 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.02.064
BaMoO4 [31–36], have been successfully prepared. Very recently, we have successfully fabricated CaWO4 and BaXO4 nanostructures at low temperature [37,38]. Here we report an attempt on the synthesis of hierarchical BaXO4 nanostructures with controlled morphologies by exploiting the oriented attachment mechanism at room temperature. Our method is simple, facile and cost-effective and is suitable for large-scale synthesis. 2. Experimental details The syntheses of BaMoO4 nanostructures were performed at room temperature. In a typical synthesis, 20 mL of aqueous solution containing 1 mM EDTA and 25 mM BaCl2 was rapidly mixed with 20 mL aqueous 15 mM Na2MoO4 solution under continuous magnetic agitation for 15 min. After aging for 12 h, the products were collected from solution by centrifugation, washed several times with distilled water and absolute alcohol, and dried in atmosphere at room temperature. The obtained products were characterized by XRD (X'Pert with Cu Kα radiation), SEM (Hitachi S-4800) and photoluminescence spectrophotometer (Perkin-Elmer LS 55). 3. Results and discussion A typical XRD pattern was shown in Fig. 1, which confirms the successful synthesis of pure body-centered tetragonal structured BaMoO4 (JCPDS No. 29-0193). Fig. 2 shows SEM images of hierarchical BaMoO4 nanostructures obtained under different reaction conditions. They exhibit peanut-like, cube-like and flower-like morphologies with good uniformity, respectively (Fig. 2a–c). The average sizes of peanut-like (long axis), cubic-like (edge length) and flower-like
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L. Ma et al. / Materials Letters 64 (2010) 1235–1237
Fig. 1. A typical XRD pattern of the products prepared with 12.5 mM BaCl2, 7.5 mM Na2MoO4 and 0.5 mM EDTA for 12 h.
(diameter) nanostructures are ∼6.26, 0.25 and 2.10 µm, respectively. The high magnification SEM images (the insets in Fig. 2a–c) show that these nanostructures with rough surfaces are assembled from many small primary nanoparticles. The morphological and size control of hierarchical nanostructures were achieved by adjusting reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio and the possible growth mechanism was discussed (see Supporting information). In this work, a similar process to the controlled synthesis of hierarchical BaMoO4 nanostructures with various morphologies was 2− carried out by simply replacing MoO2− 4 with WO4 while keeping the rest of the experimental conditions unchanged and hierarchical BaWO4 nanostructures with peanut-like, dumbbell-like, sphere-like
and flower-like morphologies were obtained (see Supporting information). With excitation at 393 nm, BaMoO4 and BaWO4 nanostructures showed the strong and broad green emission peaks at 560 and 558 nm, respectively (Fig. 3a and b). The emission peak positions were different from previous reports in the case of other hierarchical BaXO4 nanostructures [33,34,36], which mainly originate from the intrinsic tungstate and molybdate groups. The ellipsoid-like, cubiclike, flower-like, and peanut-like nanostructures showed the highest, high, middle, and lowest PL intensities, respectively, indicating great dependence on morphology and size evolution of the samples, which was consistent with several other reported BaXO4 nanostructures [33,34,36]. We speculated that the hieratical nanostructures formed by oriented attachment mechanism might contain some various stacking faults, leading to the difference of PL properties other hierarchical BaXO4 nanostructures [33,34,36]. The true factors influencing PL properties were still not clear and needed further investigation.
4. Conclusions In conclusion, we have succeeded in preparing hierarchical peanut-like, cubic-like, and flower-like BaMoO4 nanostructures in aqueous at room temperature. The morphological and size control of the hierarchical nanostructures can be achieved by adjusting reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio. This manipulation is readily extended to obtain hierarchical BaWO4 nanostructures with different morphologies in a similar process. The
Fig. 2. SEM images of products prepared with 12.5 mM BaCl2 and 7.5 mM Na2MoO4 under different EDTA concentration and reaction time. (a) 0.5 mM EDTA, 12 h, (b) 1 mM EDTA, 20 s and (c) 3 mM EDTA, 12 h.
Fig. 3. PL spectra of the obtained BaXO4 (X = Mo, W) hierarchical nanostructures at room temperature. (a) BaMoO4 and (b) BaWO4.
L. Ma et al. / Materials Letters 64 (2010) 1235–1237
methodology is expected to be extendable to produce other metal molybdate and tungstate 3D hierarchical nanostructures. Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 20371014, 20671026, 20971032 and 50772025). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi: 10.1016/j.matlet.2010.02.064. References [1] Dinsmore AD, Hsu MF, Nikolaides MG, Marquez M, Bausch AR, Weitz DA. Science 2002;298:1006–9. [2] Yang HG, Zeng HC. Angew Chem Int Ed 2004;43:5930–3. [3] Penn RL, Banfield JF. Science 1998;281:969–71. [4] Zhang YJ, Or SW, Wang XL, Cui TY, Cui WB, Zhang Y, et al. Eur J Inorg Chem 2009: 168–73. [5] Xu HL, Wang WZ, Zhu W, Zhou L, Ruan ML. Cryst Growth Des 2007;7:2720–4. [6] Liu JP, Huang XT, Li YY, Sulieman KM, He X, Sun FL. Cryst Growth Des 2006;6: 1690–6. [7] Tao F, Wang ZJ, Chen DB, Yao LZ, Cai WL, Li XG. Nanotechnology 2007:18. [8] Li DP, Zheng Z, Shui Z, Long M, Yu J, Wong KW, et al. J Phys Chem C 2008;112: 2845–50. [9] Jia C, Cheng Y, Bao F, Chen DQ, Wang YS. J Cryst Growth 2006;294:353–7. [10] Zhang DF, Sun LD, Zhang J, Yan ZG, Yan CH. Cryst Growth Des 2008;8:3609–15. [11] Gong Q, Qian XF, Ma XD, Zhu ZK. Cryst Growth Des 2006;6:1821–5.
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[12] Hawaldar RR, Sathaye SD, Harle A, Gholap RS, Patil KR. J Phys Chem C 2008;112: 7557–61. [13] Zhou YX, Yao HB, Zhang Q, Gong JY, Liu SJ, Yu SH. Inorg Chem 2009;48:1082–90. [14] Gu ZJ, Zhai TY, Gao BF, Sheng XH, Wang YB, Fu HB, et al. J Phys Chem B 2006;110: 23829–36. [15] Qian HS, Gunawan P, Zhang YX, Lin GF, Zheng JW, Xu R. Cryst Growth Des 2008;8: 1282–7. [16] Zhang HT, Chen XH. J Phys Chem B 2006;110:9442–7. [17] Blasse G, Dirksen GJ. J Solid State Chem 1981;36:124–6. [18] Caprez A, Meyer P, Mikhail P, Hulliger J. Mater Res Bull 1997;32:1045–54. [19] Afanasiev P. Mater Lett 2007;61:4622–6. [20] Cerny P, Jelinkova H, Zverev PG, Basiev TT. Prog Quant Electron 2004;28:113–43. [21] Bi J, Xiao DQ, Gao DJ, Yu P, Yu GL, Zhang W, et al. Cryst Res Technol 2003;38: 935–40. [22] Xie B, Wu Y, Jiang Y, Li FQ, Wu J, Yuan SW, et al. J Cryst Growth 2002;235:283–6. [23] Cerny P, Jelinkova H. Opt Lett 2002;27:360–2. [24] Marques APD, De Melo DMA, Paskocimas CA, Pizani PS, Joya MR, Leite ER, et al. J Solid State Chem 2006;179:671–8. [25] Yang PD, Kim F. Chemphyschem 2002;3:503–6. [26] Kwan S, Kim F, Akana J, Yang PD. Chem Commun 2001:447–8. [27] He JH, Han M, Shen XP, Xu Z. J Cryst Growth 2008;310:4581–6. [28] Luo YS, Tu YC, Yu BH, Liu JP, Li HL, Jia ZJ. Mater Lett 2007;61:5250–4. [29] Wang XM, Xu HY, Wang H, Yan H. J Cryst Growth 2005;284:254–61. [30] Wang R, Liu C, Zeng J, Li KW, Wang H. J Solid State Chem 2009;182:677–84. [31] Shi HT, Qi LM, Ma JM, Wu NZ. Adv Funct Mater 2005;15:442–50. [32] Shi HT, Wang XH, Zhao NN, Qi LM, Ma JM. J Phys Chem B 2006;110:748–53. [33] Ryu JH, Kim KM, Mhin SW, Park GS, Eun JW, Shim KB, et al. Appl Phys A-mater 2008;92:407–12. [34] Luo ZJ, Li HM, Shu HM, Wang K, Xia JX, Yan YS. Cryst Growth Des 2008;8:2275–81. [35] Ryu EK, Huh YD. B Kor Chem Soc 2008;29:503–6. [36] Wu XY, Du J, Li HB, Zhang MF, Xi BJ, Fan H, et al. J Solid State Chem 2007;180: 3288–95. [37] Yin Y, Gao Y, Sun Y, Zhou B, Ma L, Wu X, et al. Mater Lett 2010;64:602–4. [38] Yin Y, Gan Z, Sun Y, Zhou B, Zhang X, Zhang D, et al. Mater Lett 2010;64:789–92.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature Lin Ma a,1, Yuzeng Sun a,1, Peng Gao b,⁎, Yongkui Yin a,1, Zengming Qin a, Baibin Zhou a,⁎ a b
Key Laboratory of Physical and Chemical Materials, College of Heilongjiang Province, Harbin Normal University, Harbin 150025, PR China Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001, PR China
a r t i c l e
i n f o
Article history: Received 16 January 2010 Accepted 28 February 2010 Available online 6 March 2010 Keywords: Hierarchical Nanostructures Controlled synthesis BaMoO4 BaWO4
a b s t r a c t Controlled synthesis of hierarchical Barium molybdate (BaMoO4) nanostructures with different morphologies, such as peanut-like, cube-like and flower-like, was successfully achieved in aqueous solution at room temperature. The obtained products were characterized by a scanning electron microscope (SEM) and an Xray power diffractometer (XRD). The morphologies of the obtained products were found to be greatly dependent on reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio. This controllable method could be readily extended to produce hierarchical Barium tungstate (BaWO4) nanostructures with peanutlike, dumbbell-like, sphere-like and flower-like morphologies. The photoluminescence (PL) properties of the obtained BaMoO4 and BaWO4 nanostructures exhibited strong dependence on the morphologies and sizes, respectively. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The synthesis of hierarchical nanostructures with controlled shape and size is important due to their novel properties and potential applications in optics, electronics, magnetics and biology [1,2]. Recent progress shows that various hierarchical nanostructures which may involve the oriented attachment mechanism [3] at some stage have been synthesized, including butterfly-like, leave-like, sheet-like and ellipsoid-like CuO [4–6], dendritic Ag, Ag2Se and alpha-Fe2O3 [7–9], flower-like CaMoO4, SrMoO4 and ZnO [10,11], rod-like PbCrO4 [12], plate-like FeWO4 [13], urchin-like and ribbon-like WO3 [14], spindlelike alpha-GaOOH, alpha-Ga2O3 and beta-Ga2O3 [15], and spherical Co1 − xMnxO [16]. Scheelite BaXO4 (X = W, Mo) are important optoelectronic materials due to their abilities to produce strong luminescence [17] and have great potential applications such as in nuclear spin optical hole burning hosts [18], photocatalysts [19], stimulated Raman scattering [20] and all-solid-state lasers [21–23]. Recently, Marques et al. have successfully demonstrated that BaMoO4 is a highly promising candidate for photoluminescent applications [24]. The BaXO4 hierarchical nanostructures with different morphologies, such as layer-like, sheaf-like, corn-like, double-taper-like, scissors-like, fasciculus-like, dumbbell-like, kernel-like, bowknotlike and cauliflower-like and peniform-like BaWO4 [25–31] and penniform-like, flower-like, nest-like, rod-like and shuttle-like
⁎ Corresponding authors. E-mail addresses: [email protected] (B. Zhou), [email protected] (P. Gao). 1 Lin Ma, Yuzeng Sun and Yongkui Yin contributed equally to this work. 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.02.064
BaMoO4 [31–36], have been successfully prepared. Very recently, we have successfully fabricated CaWO4 and BaXO4 nanostructures at low temperature [37,38]. Here we report an attempt on the synthesis of hierarchical BaXO4 nanostructures with controlled morphologies by exploiting the oriented attachment mechanism at room temperature. Our method is simple, facile and cost-effective and is suitable for large-scale synthesis. 2. Experimental details The syntheses of BaMoO4 nanostructures were performed at room temperature. In a typical synthesis, 20 mL of aqueous solution containing 1 mM EDTA and 25 mM BaCl2 was rapidly mixed with 20 mL aqueous 15 mM Na2MoO4 solution under continuous magnetic agitation for 15 min. After aging for 12 h, the products were collected from solution by centrifugation, washed several times with distilled water and absolute alcohol, and dried in atmosphere at room temperature. The obtained products were characterized by XRD (X'Pert with Cu Kα radiation), SEM (Hitachi S-4800) and photoluminescence spectrophotometer (Perkin-Elmer LS 55). 3. Results and discussion A typical XRD pattern was shown in Fig. 1, which confirms the successful synthesis of pure body-centered tetragonal structured BaMoO4 (JCPDS No. 29-0193). Fig. 2 shows SEM images of hierarchical BaMoO4 nanostructures obtained under different reaction conditions. They exhibit peanut-like, cube-like and flower-like morphologies with good uniformity, respectively (Fig. 2a–c). The average sizes of peanut-like (long axis), cubic-like (edge length) and flower-like
1236
L. Ma et al. / Materials Letters 64 (2010) 1235–1237
Fig. 1. A typical XRD pattern of the products prepared with 12.5 mM BaCl2, 7.5 mM Na2MoO4 and 0.5 mM EDTA for 12 h.
(diameter) nanostructures are ∼6.26, 0.25 and 2.10 µm, respectively. The high magnification SEM images (the insets in Fig. 2a–c) show that these nanostructures with rough surfaces are assembled from many small primary nanoparticles. The morphological and size control of hierarchical nanostructures were achieved by adjusting reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio and the possible growth mechanism was discussed (see Supporting information). In this work, a similar process to the controlled synthesis of hierarchical BaMoO4 nanostructures with various morphologies was 2− carried out by simply replacing MoO2− 4 with WO4 while keeping the rest of the experimental conditions unchanged and hierarchical BaWO4 nanostructures with peanut-like, dumbbell-like, sphere-like
and flower-like morphologies were obtained (see Supporting information). With excitation at 393 nm, BaMoO4 and BaWO4 nanostructures showed the strong and broad green emission peaks at 560 and 558 nm, respectively (Fig. 3a and b). The emission peak positions were different from previous reports in the case of other hierarchical BaXO4 nanostructures [33,34,36], which mainly originate from the intrinsic tungstate and molybdate groups. The ellipsoid-like, cubiclike, flower-like, and peanut-like nanostructures showed the highest, high, middle, and lowest PL intensities, respectively, indicating great dependence on morphology and size evolution of the samples, which was consistent with several other reported BaXO4 nanostructures [33,34,36]. We speculated that the hieratical nanostructures formed by oriented attachment mechanism might contain some various stacking faults, leading to the difference of PL properties other hierarchical BaXO4 nanostructures [33,34,36]. The true factors influencing PL properties were still not clear and needed further investigation.
4. Conclusions In conclusion, we have succeeded in preparing hierarchical peanut-like, cubic-like, and flower-like BaMoO4 nanostructures in aqueous at room temperature. The morphological and size control of the hierarchical nanostructures can be achieved by adjusting reaction time, EDTA concentration and the [Ba2+]/[MoO2− 4 ] ratio. This manipulation is readily extended to obtain hierarchical BaWO4 nanostructures with different morphologies in a similar process. The
Fig. 2. SEM images of products prepared with 12.5 mM BaCl2 and 7.5 mM Na2MoO4 under different EDTA concentration and reaction time. (a) 0.5 mM EDTA, 12 h, (b) 1 mM EDTA, 20 s and (c) 3 mM EDTA, 12 h.
Fig. 3. PL spectra of the obtained BaXO4 (X = Mo, W) hierarchical nanostructures at room temperature. (a) BaMoO4 and (b) BaWO4.
L. Ma et al. / Materials Letters 64 (2010) 1235–1237
methodology is expected to be extendable to produce other metal molybdate and tungstate 3D hierarchical nanostructures. Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 20371014, 20671026, 20971032 and 50772025). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi: 10.1016/j.matlet.2010.02.064. References [1] Dinsmore AD, Hsu MF, Nikolaides MG, Marquez M, Bausch AR, Weitz DA. Science 2002;298:1006–9. [2] Yang HG, Zeng HC. Angew Chem Int Ed 2004;43:5930–3. [3] Penn RL, Banfield JF. Science 1998;281:969–71. [4] Zhang YJ, Or SW, Wang XL, Cui TY, Cui WB, Zhang Y, et al. Eur J Inorg Chem 2009: 168–73. [5] Xu HL, Wang WZ, Zhu W, Zhou L, Ruan ML. Cryst Growth Des 2007;7:2720–4. [6] Liu JP, Huang XT, Li YY, Sulieman KM, He X, Sun FL. Cryst Growth Des 2006;6: 1690–6. [7] Tao F, Wang ZJ, Chen DB, Yao LZ, Cai WL, Li XG. Nanotechnology 2007:18. [8] Li DP, Zheng Z, Shui Z, Long M, Yu J, Wong KW, et al. J Phys Chem C 2008;112: 2845–50. [9] Jia C, Cheng Y, Bao F, Chen DQ, Wang YS. J Cryst Growth 2006;294:353–7. [10] Zhang DF, Sun LD, Zhang J, Yan ZG, Yan CH. Cryst Growth Des 2008;8:3609–15. [11] Gong Q, Qian XF, Ma XD, Zhu ZK. Cryst Growth Des 2006;6:1821–5.
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[12] Hawaldar RR, Sathaye SD, Harle A, Gholap RS, Patil KR. J Phys Chem C 2008;112: 7557–61. [13] Zhou YX, Yao HB, Zhang Q, Gong JY, Liu SJ, Yu SH. Inorg Chem 2009;48:1082–90. [14] Gu ZJ, Zhai TY, Gao BF, Sheng XH, Wang YB, Fu HB, et al. J Phys Chem B 2006;110: 23829–36. [15] Qian HS, Gunawan P, Zhang YX, Lin GF, Zheng JW, Xu R. Cryst Growth Des 2008;8: 1282–7. [16] Zhang HT, Chen XH. J Phys Chem B 2006;110:9442–7. [17] Blasse G, Dirksen GJ. J Solid State Chem 1981;36:124–6. [18] Caprez A, Meyer P, Mikhail P, Hulliger J. Mater Res Bull 1997;32:1045–54. [19] Afanasiev P. Mater Lett 2007;61:4622–6. [20] Cerny P, Jelinkova H, Zverev PG, Basiev TT. Prog Quant Electron 2004;28:113–43. [21] Bi J, Xiao DQ, Gao DJ, Yu P, Yu GL, Zhang W, et al. Cryst Res Technol 2003;38: 935–40. [22] Xie B, Wu Y, Jiang Y, Li FQ, Wu J, Yuan SW, et al. J Cryst Growth 2002;235:283–6. [23] Cerny P, Jelinkova H. Opt Lett 2002;27:360–2. [24] Marques APD, De Melo DMA, Paskocimas CA, Pizani PS, Joya MR, Leite ER, et al. J Solid State Chem 2006;179:671–8. [25] Yang PD, Kim F. Chemphyschem 2002;3:503–6. [26] Kwan S, Kim F, Akana J, Yang PD. Chem Commun 2001:447–8. [27] He JH, Han M, Shen XP, Xu Z. J Cryst Growth 2008;310:4581–6. [28] Luo YS, Tu YC, Yu BH, Liu JP, Li HL, Jia ZJ. Mater Lett 2007;61:5250–4. [29] Wang XM, Xu HY, Wang H, Yan H. J Cryst Growth 2005;284:254–61. [30] Wang R, Liu C, Zeng J, Li KW, Wang H. J Solid State Chem 2009;182:677–84. [31] Shi HT, Qi LM, Ma JM, Wu NZ. Adv Funct Mater 2005;15:442–50. [32] Shi HT, Wang XH, Zhao NN, Qi LM, Ma JM. J Phys Chem B 2006;110:748–53. [33] Ryu JH, Kim KM, Mhin SW, Park GS, Eun JW, Shim KB, et al. Appl Phys A-mater 2008;92:407–12. [34] Luo ZJ, Li HM, Shu HM, Wang K, Xia JX, Yan YS. Cryst Growth Des 2008;8:2275–81. [35] Ryu EK, Huh YD. B Kor Chem Soc 2008;29:503–6. [36] Wu XY, Du J, Li HB, Zhang MF, Xi BJ, Fan H, et al. J Solid State Chem 2007;180: 3288–95. [37] Yin Y, Gao Y, Sun Y, Zhou B, Ma L, Wu X, et al. Mater Lett 2010;64:602–4. [38] Yin Y, Gan Z, Sun Y, Zhou B, Zhang X, Zhang D, et al. Mater Lett 2010;64:789–92.