Origin of the 4750-Å Emission in KCl: Tl Phosphors

Some experimental results concerning low-temperature emission intensity, decay times, and activator concentration dependence of the 4750-Å KCl: Tl emission are reported in order to clarify its origin. According to the experimental features, this emission is attributed to the de-excitation of the ${}_{}{}^3{}_{}{}^{}A_{1\mathrm{u}}^{}{}_{}{}^{}$ state, directly excited by the transition ${}_{}{}^1{}_{}{}^{}A_{1\mathrm{g}}^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}A_{1\mathrm{u}}^{}{}_{}{}^{}$, as an alternative to the several discordant interpretations already given.