Spectroscopy and upconversion ofCsCdBr3:Pr3+

In ${\mathrm{CsCdBr}}_3$ the trivalent Pr ions substitute the divalent Cd ions. Charge compensation leads to Pr vacancy centers. By selective excitation and fluorescence spectroscopy and by annealing the crystals, three different Pr centers could be identified. The first one is the well-known symmetric pair center ${\mathrm{Pr}}^{3+}$–${\mathrm{Cd}}^{2+}$ vacancy–${\mathrm{Pr}}^{3+}$, the second one is the asymmetric pseudopair center ${\mathrm{Pr}}^{3+}$-${\mathrm{Pr}}^{3+}$-${\mathrm{Cd}}^{2+}$ vacancy, and the third one finally is a ${\mathrm{Pr}}^{3+}$ single ion with a ${\mathrm{Cs}}^{+}$ vacancy nearby. Energy-level schemes of all three centers were deduced from polarized site-selective spectra including the symmetries of the crystal-field states. Only the ${\mathrm{Pr}}^{3+}$-${\mathrm{Pr}}^{3+}$-${\mathrm{Cd}}^{2+}$ vacancy center showed upconversion emission from ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ and ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_1$ under pulsed ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$ excitation.