Effect of uniaxial stress on exciton luminescence in CsI crystals

The exciton luminescence of undoped and doped CsI crystals of various origin and various doping has been studied in the range 4.2 to 300 K under excitation by photons of energy E < 6.2 eV. The effect of uniaxial stress supplied at 4.2 K along the [100] crystal axis on the luminescence of self-trapped excitons and various types of localized excitons has been examined. Some of the emission bands of CsI have been ascribed to various relatively large crystal lattice imperfections. For example, the bands peaking at 4.32, 4.25 and 4.03 eV have been found to arise from the on-centre configuration of localized excitons and assumed to be connected with compressed and expanded crystal lattice regions and with some larger lattice distortions or vacancy aggregates, respectively. The peculiarities of the exciton luminescence characteristics, their stress-induced changes and the classification of the excitons in CsI with respect to the lattice relaxation have been discussed.