Optical properties of theTl0(1) center in KCl

Abstract

We report both experimental and theoretical studies of the ${\mathrm{Tl}}^{0}$(1) center in KCl, a center consisting of a neutral Tl atom perturbed by the field of an adjacent anion vacancy. Absorption bands peaking at 1040, 720, 550, and 340 nm are all shown to belong to the ${\mathrm{Tl}}^{0}$(1) center. The relatively weak ($f\ensuremath{\lesssim}0.01$) bands at 1040 and 720 nm correspond to absorptions terminating on the crystal-field-split components of the ${6}^{2}{P}_{\frac{3}{2}}$ level, while the stronger band at 550 nm corresponds to transition to a state derived largely from ${7}^{2}{S}_{\frac{1}{2}}$. The sole luminescence band is the laser-active band having 1.6-\ensuremath{\mu}sec decay time and peaking at 1520 nm. The model presented here can account for the transition energies of the $6p$ manifold, including the Stokes shift between absorption (at 1040 nm) and luminescence, as well as the polarization properties and relative oscillator strengths of the 1040-, 720-, and 550-nm bands.