Emission from Mo‐O charge‐transfer state and Yb3+ emission in Eu3+‐doped and nondoped molybdates under UV excitation |
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| Authors: | Xuebin Qiao Taiju Tsuboi |
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| Affiliation: | 1. Jiangsu Key Laboratory of Advanced Laser Materials and Devices, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou, China;2. Kyoto Sangyo University, Kamigamo, Kyoto, Japan;3. Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China |
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| Abstract: | Molybdates of Li+ and Yb3+ are studied to investigate the luminescence under UV excitation. LiYb(MoO4)2 and Eu3+‐doped LiYb1‐xEux(MoO4)2 (x=001–1.0) phosphors were synthesized by solid state reaction under mixing of Eu2O3, Yb2O3, Li2CO3 and MoO2 in air atmosphere. Two broad absorption bands centered at 333 and 236 nm are observed in LiYb(MoO4)2 compound. They are attributed to the 1A1→1T1 and 1T2 transitions due to the O2?→Mo6+ electron transfers in MoO4 tetrahedron. An emission band with a peak at about 440 nm is found, which is attributed to the 3T1→1A1 transition of MoO4. Appearance of near‐infrared (NIR) Yb3+ emission observed under UV excitation is understood by the MoO4→Yb3+ Foerster‐Type energy transfer due to spectral overlap between the low‐energy tail of the broad 440 nm emission band and the high‐energy tail of the broad Yb3+ absorption band and due to short Yb3+‐MoO4 distance. Yb3+ emission observed in LiYb1?xEux(MoO4)2 by Eu3+ excitation is understood by the Eu3+→Yb3+ energy transfer by cross‐relaxation (CR) process between the 5D0→7F6 Eu3+ transition and the 2F7/2→2F5/2 Yb3+ transition. The CR efficiency shows maximum efficiency of 0.24 at x=0.15 of higher acceptor Yb3+ concentration than donor Eu3+ concentration. Three Yb3+ emission bands with peaks at 994, 1002, and 1023 nm are observed, depending on the excitation wavelength. This is explained by less‐shielded 4f electrons of Yb3+ by the 5s25p6 outermost electron shells, which are also responsible for unusual broadband Yb3+ absorption and emission. From appearance of NIR Yb3+ emission under excitation by not only UV light but also red light, these compounds are expected to be suitable for efficient photovoltaic application to Si‐based solar cells. |
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| Keywords: | europium fluorescence optical materials/properties phosphors ytterbium photoluminescence |
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