Dynamic properties of [X] centres in cesium halides

In thallium doped cesium halides, the evolution of the number of self‐trapped holes with different orientations is monitored by measuring EPR spectra intensities. With a linearly polarized excitation in a suitable geometry, the relative absorption dichroism of the individual centre is determined, i.e. the absorption cross‐section ratio with polarization parallel/perpendicular to the centre axis. It amounts to 8 ± 2 at 436 nm and 10 ± 2 at 604 nm in CsI, and to 16 ± 2 at 406 nm in CsBr. Measurements with increasing temperature indicate that the first thermoluminescent peak is due to recombination following the movement of the centres along their axis only, whereas the second peak results of 90° jumps. The critical temperatures are 58 and 86 K in CsI, 106 and 130 K in CsBr, and 146 and 167 K in CsCI.