Hot Luminescence of Self‐Trapped Excitons in Alkali Halide Crystals

The hot luminescence of self‐trapping excitons is discovered in NaI and KI single crystals. The temperature behaviour of hot emission spectra in the range of 4.2 to 170 K and the corresponding excitation spectra are studied. Basing on the theory of resonant secondary emission developed recently a description of the observed luminescence in terms of the relaxation of a configurational coordinate is given. The calculations of local lattice dynamics of a self‐trapped exciton determining its relaxation law and the shape of the hot emission spectra are presented. A comparison of the theory with the experiment provides a detailed picture of the exciton relaxation into the self‐trapped state.