【摘要】 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→⁷F_i和⁵D₄→⁷F_i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.更多还原

【Abstract】 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/aaaaaaa(4h6). The lattice parameters are: aaaaaaaa=0.5238 and c=1.1364nm for CaWO4:0.01Tb, aaaaaaaa = 0.5409 and c=1.1941nm for SrWO4:0.01Tb, and aaaaaaaa = 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 produce5D4???????????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 of5BD3??????????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.For the excited states of f?????????f transition, such as 5H7, 5L10, 5G6 and 5D3 the 5D3???????????/7Fi emissions are predominant in the lower Tb3 + concentration. When the Tb3+ concentration was increased to above 2mol%,the intensities of 5D4???????????7Fi emissions changed to be much higher than 5D3??????????Fi, despite the fact that both 5D4?????????7Fi and 5D3??????????7Fi emissions increase with an increase in concentration of Tb3+ ion. It was suggested that the probability to transfer the excitation energy from 5D3 level of one Tb3+ ion to 5D4 level of another Tb3+ ion should increase with Tb3+ ion concentration.The efficiency of energy transfer from host lattice to activator ion, the probability of O2-????????Tb3+ charge-transfer and the critical concentration of concentration quenching all decrease in the order of Ca, Sr and Ba.In SrWO4:Tb and BaWO4:Tb, the critical concentration of 5D3????????????7F, emissions is essentially the same as that of 5D4??????????7Fi emissions. But in CaWO4:Tb, it varies with different excited states. In these crystals, the concentration quenching of Tb3+ emission can be explained by the formation of Tb2(WO4)3 crystal nucleus and the dislocation in crystals.更多还原