Intrinsic Luminescence and Configurations of Self-Trapped Excitons in Alkali Halide Crystals.

系统地研究了碱金属卤化物晶体中自陷态激子(STE)在各种混晶中的辐射复合过程。结果表明，氯化钠、氯化钾、氯化钠、溴化钠、溴化钾、溴化钾、溴化钠、碘化钾和溴化钾等9种碱金属卤化物中的pi发射带应分为三种类型(I、II、III)。研究还表明，只在五种晶体--氯化钠、溴化钾、溴化铅、溴化钾、碘化钾和溴化钠中才能识别的西格玛发射带，基本上与NaBr和NaI(第I类)中所谓的“圆周率发射”带相同。这些发现给碱金属卤化物中单重态和三重态pi跃迁的出现、峰能量和偶极强度带来了令人满意的规律性。在这个新的方案中，一般的sigma带以及在NaBR和NaI中对应的pi带被认为起源于中心STE构型。认为低能pi带和RbI中的Ex带起源于两个不同的偏心STE组态，它们都位于最低能量的同一绝热势面上，因此，本研究从中心和/或偏心扭曲的角度对激子自陷机制提供了统一的认识。

Radiative recombination processes of self-trapped excitons (STE) in alkali halide crystals were studied systematically in various kinds of mixed crystals. It was found that the pi emission bands in nine alkali halides, NaCl, KCl, RbCl, NaBr, KBr, RbBr, NaI, KI and RbI, should be classified into three distinct types (I, II, III). It has also been shown that the sigma emission bands which are recognized only in five crystals, NaCl, KBr, RbBr, KI and RbI, are essentially the same as the so-called "pi emission" bands in NaBr and NaI (Type I). These findings bring a pleasing orderliness to the appearance, peak energies and dipole strengths of singlet sigma and triplet pi transitions in alkali halides. In this new scheme, the sigma bands generally, and the corresponding pi bands in NaBr and NaI, are suggested to originate from an on-center STE configuration. The low energy pi bands, and the Ex band in RbI, are suggested to originate from two separate off-center STE configurations, all on the same adiabatic potential surface of the lowest energy.Thus, the present study provides an unifying recognition for the mechanism of exciton self-trapping in terms of on-center and/or off-center distortion.