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Generally, the Eu3+-activated red phosphors suffer narrow 4f-4f excitation lines ranging from near-UV to blue part of the spectrum, resulting in poor spectral overlapping with the emission spectrum of the pumping LED and low energy conversion efficiency. In this paper, the strategy of Te6+/Mo6+ mixing is adopted to enhance the excitation bandwidth of Eu3+ via the energy transfer from Mo6+-O2- charge transfer state to Eu3+, which is crucial for LED applications. A series of (Gd1-xEux)6(Te1-yMoy)O12 red phosphors are synthesized by the solid state method at 1200 ℃. The crystal structure, morphology and luminescent properties are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescent spectrum. The XRD patterns of (Gd1-xEux)6(Te1-yMoy) O12 (x = 0.2, y = 0, 0.4) match well with that of Gd6TeO12 (JCPDS No. 50-0269), but differ from that of Gd6MoO12 (JCPDS No. 24-1085). The phosphor consists of irregular particles with an average size of 10 m. Upon excitation at 393 nm, the (Gd1-xEux)6TeO12 phosphors emit red light corresponding to the intraconfigurational 4f-4f transitions of Eu3+, and the color coordinates are calculated to be (0.647, 0.353). The 5D07F2 electron-dipole transition dominates the emission spectrum, which reveals that Eu3+ occupies a crystallographic site without an inversion center. Moreover, this transition gives rise to three distinguishable emission lines situated at 605, 618, and 632 nm, respectively. This unusual spectral splitting is supposed to originate from the strong interaction exerted by the crystal field of host on the 4f electrons. The optimum doping content of Eu3+ in (Gd1-xEux)6TeO12 phosphor is 20% (mole fraction), the critical distance for energy transfer is 0.75 nm, and the concentration quenching is confirmed to be induced by the dipole-dipole interaction from the linear relationship between lg(I/x) and lg x (I represents the luminescence intensity, and x represents the doping concentration of Eu3+). As the temperature increases, the emission intensity decreases gradually due to thermal quenching. The integrated emission intensity at 423 K is 70% of the initial value at ambient temperature. The thermal activation energy is determined to be 0.1796 eV from the temperature dependence of luminescence intensities. The partial substitution of Te6+ by Mo6+ does not change the emission position nor intensity significantly, but promotes the excitation bandwidth and conversion efficiency remarkably. Compared with (Gd0.8Eu0.2)6TeO12, the compositionoptimized (Gd0.8Eu0.2)6(Te0.6Mo0.4)O12 presents a relatively flat excitation spectrum in the near-UV region. It also provides more intense emission since (Gd0.8Eu0.2)6MoO12 undergoes the strong concentration quenching arising from the high density of [MoO6] groups. In conclusion, the results indicate that (Gd0.8Eu0.2)6(Te0.6Mo0.4)O12 can serve as a broadband-excited red phosphor for near-UV-based white LEDs.
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Keywords:
- LED /
- tellurate /
- solid state method /
- red phosphor
[1] Pust P, Schmidit P J, Schnick W 2015 Nat. Mater. 14 454
[2] Mckittick J, Shea-Rohwer L E 2014 J. Am. Ceram. Soc. 97 1327
[3] Ye S, Xiao F, Pan Y X, Ma Y Y, Zhang Q Y 2010 Mater. Sci. Eng. R. 71 1
[4] Smet P F, Parmentier A B, Poelman D 2011 J. Electrochem. Soc. 158 R37
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[15] Hao M R, Li G F, He W W 2013 J. Chin. Ceram. Soc. 12 1730 (in Chinese) [郝敏如, 李桂芳, 贺文文 2013 硅酸盐学报 12 1730]
[16] Sha R, Gao W, Liu Y P 2013 Chinese Journal of Luminescence 34 1469 (in Chinese) [莎仁, 高娃, 刘叶平 2013 发光学报 34 1469]
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[18] Dou X H, Zhao W R, Song E H, Fang X B, Deng L L 2011 Proceedings of 2011 China Functional Materials Technology and Industry Forum, Chongqing, November 16-19, 2011 463 (in Chinese) [豆喜华,赵韦人,宋恩海, 方夏冰, 邓玲玲 2011 中国功能材料科技与产业高层论坛, 重庆, 11月16-19日, 2011 463]
[19] Blasse G 1986 J. Solid State Chem. 62 207
[20] Zhang N M, Guo C F, Zheng J M, Su X Y, Zhao J 2014 J. Mater. Chem. C 2 3988
[21] Chang Y C, Liang C H, Yan S A, Chang Y S 2010 J. Phys. Chen. C 114 3645
[22] Baginskiy I, Liu R S 2009 J. Electrochem. Soc. 156 G29
[23] Thangaraju D, Durirajan A, Balaji D, Babu S M, Hayakawa Y 2013 J. Lumin. 134 244
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[1] Pust P, Schmidit P J, Schnick W 2015 Nat. Mater. 14 454
[2] Mckittick J, Shea-Rohwer L E 2014 J. Am. Ceram. Soc. 97 1327
[3] Ye S, Xiao F, Pan Y X, Ma Y Y, Zhang Q Y 2010 Mater. Sci. Eng. R. 71 1
[4] Smet P F, Parmentier A B, Poelman D 2011 J. Electrochem. Soc. 158 R37
[5] Peng M Y, Yin X W, Tanner P A, Brik M G, Li P F 2015 Chem. Mater. 27 2938
[6] McKittrich J, Hannah M E, Piquette A, Han J K, Choi J I, Anc M, Galvez M, Lu-gauer H, Talbot J B, Mishra K C 2013 ECS J. Solid State Sci. Technol. 2 R3119
[7] Liu W Q, Chao K F, Wu W J, Bao F Q, Zhou B Q 2016 Acta Phys. Sin. 65 207801 (in Chinese) [刘文全, 朝克夫, 武文杰, 包富泉, 周炳卿 2016 物理学报 65 207801]
[8] Xie R J, Hirosaki N 2007 Sci. Technol. Adv. Mat. 8 588
[9] Qin L, Wei D, Huang Y L, Sun I K, Yu Y M 2013 J. Nanopart. Res. 5 1
[10] Liu Y, Wang Y, Wang L, Yu S H 2014 RSC Adv. 4 4754
[11] 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 物理学报 64 107803]
[12] Dutta P S, Khanna A 2013 ECS J. Solid State Sci. Technol. 2 R3153
[13] Li H Y, Yang H K, Moon B K, Jeong J H 2011 Inog. Chem. 50 12522
[14] Li H Y, Yang H K, Moon B K, Choi B C, Jeong J H 2011 J. Mater. Chem. 21 4531
[15] Hao M R, Li G F, He W W 2013 J. Chin. Ceram. Soc. 12 1730 (in Chinese) [郝敏如, 李桂芳, 贺文文 2013 硅酸盐学报 12 1730]
[16] Sha R, Gao W, Liu Y P 2013 Chinese Journal of Luminescence 34 1469 (in Chinese) [莎仁, 高娃, 刘叶平 2013 发光学报 34 1469]
[17] Meng Q Y, Zhang Q, Li M, Liu L F, Qu X R, Wan W L, Sun J T 2012 Acta Phys. Sin. 61 107804 (in Chinese) [孟庆裕, 张庆, 李明, 刘林峰, 曲秀荣, 万维龙, 孙江亭 2012 物理学报 61 107804]
[18] Dou X H, Zhao W R, Song E H, Fang X B, Deng L L 2011 Proceedings of 2011 China Functional Materials Technology and Industry Forum, Chongqing, November 16-19, 2011 463 (in Chinese) [豆喜华,赵韦人,宋恩海, 方夏冰, 邓玲玲 2011 中国功能材料科技与产业高层论坛, 重庆, 11月16-19日, 2011 463]
[19] Blasse G 1986 J. Solid State Chem. 62 207
[20] Zhang N M, Guo C F, Zheng J M, Su X Y, Zhao J 2014 J. Mater. Chem. C 2 3988
[21] Chang Y C, Liang C H, Yan S A, Chang Y S 2010 J. Phys. Chen. C 114 3645
[22] Baginskiy I, Liu R S 2009 J. Electrochem. Soc. 156 G29
[23] Thangaraju D, Durirajan A, Balaji D, Babu S M, Hayakawa Y 2013 J. Lumin. 134 244
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