Vacuum ultraviolet excitation and emission properties of Pr3+ and Ce3+ in MSO4 (M=Ba, Sr, and Ca) and predicting quantum splitting by Pr3+ in oxides and fluorides

Abstract

The excitation and emission properties of ${\mathrm{Pr}}^{3+}$ and ${\mathrm{Ce}}^{3+}$ doped $M{\mathrm{SO}}_4$ ${(M}^{2+}={\mathrm{Ca}}^{2+},$ ${\mathrm{Sr}}^{2+},$ and ${\mathrm{Ba}}^{2+})$ were investigated at 293 and 10 K. The lowest $5d$ level in ${\mathrm{CaSO}}_4:{\mathrm{Pr}}^{3+}$ is located below the ${4f}^2{[}^1{S}_0]$ level resulting in allowed $4f5\overrightarrow{d}{4f}^2$ transitions. In ${\mathrm{BaSO}}_4$ and ${\mathrm{SrSO}}_4$ the lowest $5d$ level appears above the ${}^1{S}_0$ level and ${4f}^2{[}^1{S}_0\overrightarrow{]}{4f}^2$ emission is observed. However, also $4f5\overrightarrow{d}{4f}^2$ emission occurs, suggesting the presence of two different Pr centers. The unusual temperature dependence of the emission, points, however, to a thermal excitation process from the ${}^1{S}_0$ state to the $4f5d$ states involving only one site. The internal quantum efficiency of the ${}^3{P}_0$ and ${}^1{D}_2$ emission in ${\mathrm{BaSO}}_4$ is estimated to be 0.1 and 1 %, respectively. It will be demonstrated that under host lattice excitation part of the energy is transferred to ${4f}^2$ states with lower energy than the ${}^1{S}_0$ or the $4f5d$ states. The possibility for quantum splitting to occur in ${\mathrm{Pr}}^{3+}$ doped oxides and fluorides will be discussed. Trends observed in the interaction between the crystal field and the $5d$ electron of ${\mathrm{Ce}}^{3+},$ will be applied to predict the energy of the $4f5d$ states of ${\mathrm{Pr}}^{3+}.$