掺杂三价铽离子的碱土金属钨酸盐的光谱特性研究

本文合成了一系列掺杂三价铽离子的碱土金属钨酸盐,测定了晶体的X射线粉末衍射数据及发射光谱和激发光谱.所合成的化合物均属四方晶系,I41/a空间群,晶胞多数随金属离子半径的增大而增大.研究了在这些晶体中三价铽离子5D3→7Fi和5D4→7Fi跃迁发射的激发态及其能量传递机理和浓度猝灭机制.讨论了发射光谱和激发光谱与铽离子浓度、金属离子半径及铽离子在晶体中的溶解度的关系.

SPECTROSCOPY OF Tb3+-DOPED ALKALI-EARTH METAL TUNGSTATES

The Tb3+-doped calcium, strontium and barium tungstates have been prepared. The emission and excitation spectra were studied. The X-ray powder diffraction data reveals that these compounds are all tetragonal crystals, space group I41/a(C4h6). The lattice parameters are: a=0.5238 and c=1.1364nm for CaWO4:0.01Tb, a=0.5409 and c=1.1941nm for SrWO4:0.01Tb, and a=0,5611, c=1.2712nm for BaWO4:0.01Tb. The alka-liearth metal atoms are coordinated with eight oxygen atoms.In these compounds, the Tb3+ ion substitutes the site of alkali-earth metal ion and does not occupy a site with a centre of symmetry, and shows relatively strong emissions of 5D3→7F6, 7F6, 7F4 and 5D4→7F6, 7F5 transitions, and the weaker emission of 5D3→7F3, 7F2 and 5D4→7F3, 7F4 transitions under excitation with 254nm radiation. There are four types of excited state to produce 5D4→7Fi emissions: (a) the excited state of O2-(2p)→W6+(5d) charge-transfer in tungstate groups (the excitation energy can be transferred from the host lattice to the 5D4 energy level of Tb3+ ion), (b) that of O2-(2p)→Tb3+(4f) charge-transfer, (c) that of 4f8→4f75d transition of Tb3+ ion and (d) 4f→4f transition of Tb3+ ion. In the case of 5D3→7Fi emission, the excited state only has three types of (b), (c) and (d). The excitation energy levels of (a) can not be transfered to energy levels of 5D3 and above.