OPTICAL STUDIES OF SELF-TRAPPED EXCITONS IN CSCL AND CSBR

Optical properties of self-trapped excitons (STE's) in CsCl and CsBr have been studied. An intrinsic luminescence band due to STE's is found, for the first time, to occur at 2.92 eV in CsCl. Transient optical-absorption spectra originating in the initial state of the STE luminescence are measured; the lowest absorption peak appears at 1.74 eV in CsCl and at 1.19 eV in CsBr. Temperature dependences of the intensity and decay time of the emission bands are also measured and analyzed to get parameters characterizing interlevel transition and quenching processes at the initial state of the luminescence. The relaxed configuration of excitons in cesium halides is discussed on the basis of the obtained results, in connection with the current model on STE's proposed for alkali halides.