Luminescent Decay of Localized Optical Excitations in KCl

As part of an effort to study absorption, luminescence, and thermal excitation with the same simple impurity system in a KCl single crystal, the luminescence arising from the optical excitation of iodine ions in KCl was measured. The excitation and emission spectra and the yield curves were determined in detail for different concentrations of iodine in the lattice between helium and room temperature and for various exciting photon energies. Results obtained for the thermal broadening of the emission bands, as well as previous results on the thermal broadening of absorption bands can be understood in terms of a simple Franck-Condon model. The existence of 3 emission bands, the observed large Stokes shift, and widely different half-widths of the bands suggest that different excited states are involved in the absorption and emission processes.