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采用水热法成功制备了Er3+/Yb3+共掺杂的NaYF4和LiYF4微米晶体. 通过X射线衍射仪和环境扫描电子显微镜对样品的晶体结构及形貌进行表征. 实验结果表明: 六方相NaYF4微米晶体为棒状结构, 而四方相LiYF4微米晶体则为八面体结构. 在近红外光980 nm激发下, NaYF4:Yb3+/Er3+和LiYF4:Yb3+/Er3+ 微米晶体均展现出很强上转换荧光发射. 且NaYF4:Yb3+/Er3+微米晶体的荧光发射强度大约是LiYF4:Yb3+/Er3+微米晶体的2倍, 但红绿比明显较低. 根据荧光光谱, 并借助激光光谱学及发光动力学深入探讨基质变化及表面修饰剂乙二胺四乙二酸(EDTA)对荧光特性的影响. 实验结果发现: 影响荧光强度的主要因素是基质环境的局域对称性, 而导致不同红绿比则是由于样品表面较多的EDTA分子所引起. Er3+掺杂的NaYF4和LiYF4 微米晶体呈现出很强的绿光发射可被应用于全色显示, 荧光粉和微光电子器件中.Lanthanide-doped upconverting fluoride nano-and micro-materials have aroused much research interest due to their potential applications in phosphors, color displays, optical storages, solid-state lasers, solar cells and biomedical imaging. In order to synthesize Ln3+ doped crystals with favorable optical properties, such as high upconversion (UC) efficiency and controllable emission profile, the two major parameters that affect luminescence processes including host materials and lanthanide activator ions should be selected appropriately in the synthesis process. Majority of scientists deem that lanthanide doped fluoride nano-and micro-materials with low phonon energy are currently the efficient UC host materials. In this work, Yb3+ and Er3+ ions codoped NaYF4 and LiYF4 microcrystals are synthesized by a facile hydrothermal method with ethylene diamine tetraacetic acid (EDTA) as a chelator. The NaYF4:Yb3+/Er3+ and LiYF4:Yb3+/Er3+ microcrystals are characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), and the photo-luminescence spectra method. The influences of EDTA on the crystal phase, shape and upconversion luminescence are explored in detail. According to the results of XRD and SEM, the pure hexagonal phased NaYF4:Yb3+/Er3+ rod-like microcrystals each with smooth surface are all around 12 m in the length. While the pure tetragonal phased LiYF4: Yb3+/Er3+ microcrystals each with smooth surface are octahedral in shape, and their average size is around 12 m. Under near infrared (NIR) 980 nm excitation, the two dominant emission peaks of Er3+ ions at 544 nm and at 650 nm are observed in NaYF4 and LiYF4 microcrystals, which can be assigned to the transitions of (2H11/2/4S3/2)4I15/2 and 4F9/24I15/2, respectively. It is found that the upconversion luminescence intensity of NaYF4:Yb3+/Er3+ microcrystals is about two times that of LiYF4:Yb3+/Er3+ microcrystals under the same excitation conditions. The ratio of red-to-green emission of Er3+ ions in LiYF4 microcrystals is higher than that of the NaYF4:Yb3+/Er3+microcrystals. The changes of the spectra in the different hosts could stem from two sources: one is that the nonradiation relaxation probability relative to phonon energy of matrix, the other is that the radiative transition probability relative to the site symmetry of the crystal field acting on the ion. The ratios between 5D07F1 and 5D07F2 transitions of Eu3+ ions in NaYF4:Yb3+/Eu3+ and LiYF4:Yb3+/Eu3+ microcrystals are employed to compare and elucidate the site symmetry of the crystal field for Ln3+ ions. Note that the ratio of 5D07F1 and 5D07F2 transitions in NaYF4:Yb3+/Eu3+ microcrystals is smaller than that of the LiYF4:Yb3+/Eu3+ microcrystals, which indicates a much higher radiative relaxation rate in NaYF4 microcrystals than in LiYF4 microcrystals. The organic ligands of EDTA on the surface of microparticles affect the properties of luminescence through changing the nonradiative relaxation rate, resulting in the different R/G ratios in NaYF4 and LiYF4 microcrystals. This result can be further supported by the comparison between NaYF4 and LiYF4 microcrystals without EDTA added in the preparation process. The micro-sized luminescence materials usually present stronger upconversion luminescence because of their higher degree of crystallinity and less surface quenching centers. Thus, the Er3+ codoped NaYF4 and LiYF4 microcrystals exhibit strong green upconversion emission, which has potential applications in full-color displays and microelectronic devices.
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Keywords:
- NaYF4 crystals /
- LiYF4 crystals /
- upconversion luminescence /
- local symmetry
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[34] Judd B R 1962 Phys. Rev. 127 750
[35] Ofelt G S 1962 J. Chem. Phys. 37 511
[36] Kirby A F, Richardson F S 1983 J. Phys. Chem. 87 2544
[37] Tsang W S, Yu W M, Mak C L, Tsui1 W L, Wong K H, Hui1et H K 2002 J. Appl. Phys. 91 1871
[38] Chen X P, Zhang Q Y, Yang C H, Chen D D, Zhao C 2009 Spectrochim. Acta A 74 441
[39] Lu C H, Huang W J, Ni Y R, Xu Z Z 2011 Mater. Res. Bull. 46 216
[40] Gao W, Zheng H R, He E J, Lu Y, Gao F Q 2014 J. Lumin. 152 44
[41] Zhao J W, Sun Y J, Kong X G, Tian L J, Wang Y, Tu L P, Zhao J L, Zhang H 2008 J. Chem. Phys. B 112 15666
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[1] Danielson E, Devenney M, Giaquinta D M, Golden J H, Haushalter R C, McFarland E W, Poojary D M, Reaves C M, Weinberg W H, Wu X D 1998 Science 279 837
[2] Zhao C, Meng Q Y, Sun W J 2015 Acta Phys. Sin. 64 107803 (in Chinese) [赵聪, 孟庆裕, 孙文军 2015 64 107803]
[3] Shalav A, Richards B S, Trupke T, Krmer K W, Gdel H U 2005 Appl. Phys. Lett. 86 13503
[4] Dong H, Sun L D, Yan C H 2015 Chem. Soc. Rev. 44 1608
[5] Zheng W, Huang P, Tu D T, Ma E, Zhu H M, Chen X Y 2015 Chem. Soc. Rev. 44 1379
[6] Wang L, Yan R, Huo Z Y, Wang L, Zeng J H, Bao J, Wang X, Peng Q, Li Y D 2005 Angew. Chem. Int. Ed. 44 6054
[7] Lima M E, Lee Y L, Zhang Y, Chu J J H 2012 Biomaterials 33 1912
[8] Gao D L, Zhang X Y, Gao W 2012 J. Appl. Phys. 111 033505
[9] Gao D L, Zheng H R, Tian Y, Lei Y, Cui M, He E J, Zhang X S 2010 Sci. Sin. Phys, Mech. Astron. 40 287 (in Chinese) [高当丽, 郑海荣, 田宇, 雷瑜, 崔敏, 何恩节, 张喜生 2010 中国科学: 物理学 力学 天文学 40 287]
[10] Fu J, Fu X, Wang C M, Yang X F, Zhuang J L, Zhang G G, Lai B Y, Wu M M, Wang J 2013 Eur. J. Inorg. Chem. 8 1269
[11] Mai H X, Zhang Y W, Sun L D, Yan C H 2007 J. Phys. Chem. C 111 13721
[12] Sun L D, Dong H, Zhang P Z, Yan C H 2015 Annu. Rev. Phys. Chem. 66 619
[13] Zhang F, Wan Y, Yu T, Zhang F Q, Shi Y F, Xie S H, Li Y G, Xu L, Tu B, Zhao D Y 2007 Angew. Chem. Int. Ed. 46 7976
[14] Ma D K, Yang D P, Cai P, Huang S M 2010 Cryst. Eng. Comm. 12 1650
[15] Zhuang J L, Wang J, Yang X F, Williams I D, Zhang W, Zhang Q Y, Feng Z M, Yang Z M, Liang C L, Wu M M, Su Q 2009 Chem. Mater. 21 160
[16] Sun Y J, Chen Y, Tian L J, Yu Y, Kong X G1, Zhao J W, Zhang H 2007 Nanotechnology 18 275609
[17] Zhang F, Che R C, Li X M, Yao C, Yang J P, Shen D K, Hu P, Li W, Zhao D Y 2012 Nano. Lett. 12 2852
[18] Wang Y, Tu L P, Zhao J W, Sun Y J, Kong X H, Zhang H 2009 J. Phys. Chem. C. 113 7164
[19] Song J B, Ni Y R, Xu Z Z 2013 J. Mater. Sci. 48 4989
[20] Gao W, Zheng H R, Han Q Y, He E J, Wang R B 2014 Cryst. Eng. Comm. 16 6697
[21] Ma D K, Yang D P, Jiang J L, Cai P, Huang S M 2010 Cryst. Eng. Comm. 12 1650
[22] Wang Q, Qu J B, Song Z G, Zhou D C, Xu X H 2014 Chin. Phys. B 23 064211
[23] Yi J, Qu J B, Wang Y A, Zhou D C 2014 Chin. Phys. B 23 0104224
[24] Liang Z Q, Zhao S L, Cun Y, Tian L J, Zhang J J, Xu Z 2015 Chin. Phys. B 24 037801
[25] Yang J Z, Qiu J B, Yang Z W, Song Z G, Yang Y, Zhou D C 2015 Acta Phys. Sin. 64 138101 (in Chinese) [杨健芝, 邱建备, 杨正文, 宋志国, 杨勇, 周大成 2015 64 138101]
[26] Dou Q Q, Zhang Y 2011 Langmuir 27 13236
[27] Zhang X Y, Wang M Q, Ding J J, Deng J P, Ran C X, Yang Z 2014 Dalton Trans. 43 5453
[28] Mahalingam V, Naccache R, Vetrone F, Capobianco J A 2009 Chem.-Eur. J. 15 9660
[29] Mahalingam V, Vetrone F, Naccache R, Speghini A, Capobianco J 2009 Adv. Mater. 21 4025
[30] Chen G Y, Ohulchanskyy T Y, Kachynski A, gren H, Prasa P N 2011 ACS Nano 5 4981
[31] Gao W, Zheng H R, Li J, Gao D L, He E J, Tu Y X 2012 Sci. Sin. Phys. Mech. Astron. 42 1003 (in Chinese) [高 伟, 郑海荣, 李娇, 高当丽, 何恩节, 涂银勋2012 中国科学: 物理学 力学 天文学 42 1003]
[32] Ding M Y, Lu C H, Cao L H, Huang W J, Nia Y R, Xu Z Z 2013 Cryst. Eng. Comm. 15 6015
[33] Zhuang J L, Liang L F, Sung H H Y, Yang X F, Wu M M, Williams I D, Feng S H, Su Q 2007 Inorg. Chem. 46 5404
[34] Judd B R 1962 Phys. Rev. 127 750
[35] Ofelt G S 1962 J. Chem. Phys. 37 511
[36] Kirby A F, Richardson F S 1983 J. Phys. Chem. 87 2544
[37] Tsang W S, Yu W M, Mak C L, Tsui1 W L, Wong K H, Hui1et H K 2002 J. Appl. Phys. 91 1871
[38] Chen X P, Zhang Q Y, Yang C H, Chen D D, Zhao C 2009 Spectrochim. Acta A 74 441
[39] Lu C H, Huang W J, Ni Y R, Xu Z Z 2011 Mater. Res. Bull. 46 216
[40] Gao W, Zheng H R, He E J, Lu Y, Gao F Q 2014 J. Lumin. 152 44
[41] Zhao J W, Sun Y J, Kong X G, Tian L J, Wang Y, Tu L P, Zhao J L, Zhang H 2008 J. Chem. Phys. B 112 15666
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