Luminescence of Tl+ ions in a KZnF3 crystal

The luminescence spectra of a KZnF3: Tl+ crystal are investigated in the energy range from 4.75 to 5.9 eV at temperatures of 10–300 K upon excitation into the A absorption band (5.7–6.3 eV). At T=300 K, the luminescence spectra exhibit an intense band with a maximum at 5.45 eV, which is attributed to single Tl+ ions substituted for K+ ions. The 5.723-eV intense narrow band observed at T<20 K is assigned to the 3Γ1u-1Γ1g zero-phonon transition, which is weakly allowed by the hyperfine interaction. The luminescence decay is studied as a function of temperature. The main characteristics of the luminescence spectra are adequately described in terms of the semiclassical theory based on the Franck-Condon principle and the Jahn-Teller effect for an excited sp configuration of the Tl+ ion with the use of the parameters obtained earlier from analyzing the absorption spectra of the system under investigation.