Abstract
The decay time measurements have been carried out on the self-trapped exciton (STE) luminescence in CdBr 2, CdCl 2 and CdCl 2CdBr 2 mixed crystals. The strong STE luminescence is observed at low temperatures below 50 K in the near ultra-violet region (UV-luminescence) having the peak at 3.26 eV in CdBr 2 and 3.76 eV in CdCl 2. In the decay curve of the UV-luminescence appear two components, the fast one with the ns life time and the slow one with the μs life time which are related to the spin-singlet and -triplet STE's, respectively. The time integrated intensity ratio of the singlet to the triplet component is much smaller in CdBr 2 (0.064) than in CdCl 2 (32) reflecting the difference in strength of spin-orbit interaction between Br − and Cl −. In the mixed crystals of CdCl 2(1− x) CdBr 2( x) , the value of the time integrated intensity decreases rapidly with small increase of the CdBr 2 content, x, from the value in CdCl 2 to that in CdBr 2. This means that the STE state strongly depends on the Br − content. The experimental results are explained by means of a structural model for the STE in cadmium halide crystals, namely, the excited states of [Cd 2+X 6 −] 4− complex molecular ions with D 3 d symmetry.
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