Nature and peculiarities of the electron-vibronic interaction in the centers of 'ORANGE' luminescence of thallium iodide crystals

Raman, photoluminescence, and photoexcitation spectra of thallium iodide crystals 'pure' and doped by chromate anions are examined. At low temperatures, these crystals show extensive structured 'orange' luminescence. On the basis of theoretical models used for the analysis of spectra, the molecular nature of emission centers is established. The adduced reasons prove the possibility of the forming of molecular radicals Cr)3 I- that are derivative of Cr O42- anions. It is these radicals that can be responsible for the observed luminescent radiation. The assumption about a triplet-singlet character of the radiation transition is made, and parameters which characterize the interaction between electron transitions and local modes of luminescence centers are estimated