Effect of uniaxial stress on exciton luminescence in CsI crystals

The exciton luminescence of undoped and doped CsI crystals of various origi n and various doping has been studied in the range 4.2 to 300 K under excit ation by photons of energy E < 6.2 eV. The effect of uniaxial stress suppli ed at 4.2 K along the [100] crystal axis on the luminescence of self-trappe d 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, 4.2 5 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 vacanc y aggregates, respectively. The peculiarities of the exciton luminescence c haracteristics, their stress-induced changes and the classification of the excitons in CsI with respect to the lattice relaxation have been discussed.