摘要
本文研究了基质发光材料Na_5Eu(MoO_4)_4和NaEu(MoO_4)_2的喇曼光谱.用群论方法分析了它们的内、外振动模式,对实验振动模进行了指认.本文还将上述喇曼光谱与Na_5Eu(WO_4)_4、CaWO_4、SrWO_4、CaMoO_4和SrMoO_4的喇曼光谱进行了比较,Na_5Eu(MoO_4)_4和NaEu(MoO_4)_2的喇曼光谱结果表明(MoO_4)^(2-)离子团的高能量拉伸内振动是产生Eu^(3+)的~5D_2→~5D_1,~5D_1→~5D_0^-多声子无辐射弛豫的原因,这导致了Eu^(3+)在这类材料中主要产生~5D_O→~7F_i的发光跃迁.
Na5Eu(MoO4)4 and NaEu(MoO4)2 are stoichiorr.etric host luminescent materials having high concentration of luminescent Eu3+ ions and no noticeable concentration quenching. Raman spectra of these two materials have been studied. The symmetry species of the lattice vibration modes of Na5Eu(MoO4)4 have been analysed by means of the group theory.The structures of both materials belong to tetragonal , I4,/aaaaaaa (C4h6) space group. For Na5Eu(Mo4)4, the free ion symmetries of (MoO4)2-, Eu3+ and Na1 + correlate with factor group C4h through their site groups. A primitive cell includes two Na5Eu(MoO4)4 molecules. It mears that 8 (MoO4)42-, 10 Na1+ and 2 Eu3 + are included in the cell. So the lattice vibration of Na5Eu(MoO4)4 in the cell can be classified into 72 internal modes and 84 external modes. For crystal factor group C4h, the Ag,Bg and Eg modes are Raman active and Au and Eu modes are infrared active.The comparison of Raman spectra of Na5Eu(MoO4)4 and NaEu(Mo-O4)2 with Na5Eu(WO4)4, CaMoO4, SrMoO4, CaWO4 and S1WO4 (all these materials in scheelite structure,I41/aaaaaaaaaaaaaaaaaa space group) has been made. The results show that the internal vibration modes (v1, v2, v3 and v4 ) are determined by (MoO4)2- or (WO4)2- ions. Substituting Mp ions instead of W ions, the wavenumbers of v2, v3 and v4 have not obvious change and only the wavenumber of v4 increases about 22 cm-1.According to Raman spectra of Na5Eu(MoO4)4 and NaEu(MoO4)2, the internal stretching vibration modes of (MoO4)2- ions have high vib-rational energy of 740-995cm-1. It causes the multiphonon nonradiation transition in this kind of scheelite structure material from 6D2 to 5D1 and 5D1 to 5D0 of Eu5 + and leads the transitions of 5D2 and 5D1 to 7Fi to be quenched and Eu3+ ions to emit 5D0 to 7Fi (j = l, 2, 3, 4) emissions mainly at room temperature.
出处
《发光学报》
EI
CAS
CSCD
北大核心
1991年第3期244-253,共10页
Chinese Journal of Luminescence
