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

系统地研究了碱卤化物晶体中自俘获激子（STE）在各种混合晶体中的辐射复合过程。结果表明，NaCl、KCl、RbCl、NaBr、KBr、RbBr、NaI、KI、RbI等9种卤化物的pi发射谱带可分为I、II、III三类。研究还表明，仅在NaCl、KBr、RbBr、KI和RbI五种晶体中识别的sigma发射带与NaBr和NaI （I型）中的所谓“pi发射”带基本相同。这些发现给碱卤化物中单线态σ和三重态π跃迁的外观、峰值能量和偶极子强度带来了令人满意的规律性。在这个新方案中，一般的sigma波段以及NaBr和NaI中相应的pi波段都来自于一个中心上的STE结构。低能pi带和RbI中的Ex带可能来自两个独立的偏离中心的STE构型，它们都位于同一绝热势面的最低能量上。因此，本研究从中心和/或偏离中心畸变的角度对激子自捕获的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.