Luminescence from KCl: I at Low Temperatures

Abstract

In addition to the well-known three impurity emission bands (BG-, B-, and UV-emission), a new emission band is found at 5.88 eV in a KCl: I system under excitation with UV-light, X-rays, or N₂ laser light. Its intensity and lifetime (0.52 μs at 9 K) fall off rapidly above 12 K with an activation energy of ΔE=21 meV. The intensities of the new emission and the BG emission are anti-correlated with varying temperature. Measurements of the excitation spectrum confirm that the 5.88 eV emission arises from de-excitation of localized excitons at I⁻ monomer ion sites.
Based on the small Stokes shift (0.82 eV) and small halfwidth (0.23 eV) of this emission band, and the results obtained in an experiment of recombination luminescence of X-rayed crystal, one-center model for relaxed excitons is suggested as the origin of a relaxed excited state responsible for the 5.88 eV emission band.