Upconversion in CsCdBr3:Pr3+

Abstract In CsCdBr3 the trivalent Pr ions substitute the divalent Cd ions. Charge compensation leads to three Pr-vacancy centers. The first one is the well known symmetric pair center Pr3+-Cd vacancy—Pr3+ the second one is the asymmetric pseudopair center Pr3+-Pr3+-Cd vacancy, and the third one finally is a Pr3+ single ion with a Cs vacancy nearby. Only the Pr3+-Pr3+-Cd vacancy center showed upconversion emission from 3 P 0 and 3 P 1 under 1D2 excitation. The dynamics of the upconversion process is studied. It cannot be explained in the standard picture of phonon-assisted cross relaxation in the energy level scheme of the rare-earth ions. In our interpretation it is made up by a cooperative energy transfer from the doubly excited pair state 1D2 × 1D2 to lattice excitons followed by a back transfer of the energy exciting the pair into the states 3P1 × 3H4, 3P0 × 3H4, and 1D2 × 3H6, First experiments on CsCdBr3:Tm3+ confirm the picture of exciton-mediated upconversion.