Oscillator-strength ratios for the two principal impurity absorption bands of KCl: Tl and KCl: In are calculated including the effect of crystalline interactions. The phosphor KCl: In was devised in order to provide an additional check of the theoretical analysis. The excited impurity states are assumed to be of the nature of ${}_{}{}^1{}_{}{}^{}P_{}^0{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_{}^0{}_{}{}^{}$ states of the $\mathrm{sp}$ configuration mixed by spin-orbit interaction. Spin-orbit coupling constants are obtained from free-ion spectra. Crystal interactions are included by using experimental transition energies for the crystal to calculate the energy separation of the pure singlet and triplet states in the crystal. The calculated oscillator-strength ratios are in satisfactory agreement with experiment.

• Received 28 June 1957

DOI:https://doi.org/10.1103/PhysRev.108.46