Cooperative processes and upconversion in Cs2NaYCl6 codoped with Os4+ and Er3+ - art. no. 245118

Halide lattices singly doped with Os4+ or Er3+ are both known to show visib le upconversion luminescence upon excitation around 10 000 cm(-1). In this study, we analyze the cooperative processes in Cs2NaYCl6 codoped with Os4and Er3+ by measuring luminescence intensities and lifetimes. The excitatio n energy is found to be transferred from the Gamma (5)(T-1(2g))/Gamma (3)(E -1(g)) states of Os4+ to I-4(11/2) and I-4(13/2) of Er3+. These initial ste ps are followed by upconversion processes leading to Er3+ S-4(3/2) upconver sion emission. The upconversion efficiency upon excitation into Gamma (5)(T -1(2g))/Gamma (3)(E-1(g)) of Os4+ critically depends on the Er3+ concentrat ion, and among the Cs2NaYCl6:x%Er3+, 0.1% Os4+ (x=2, 10, and 100) samples i t is highest for x=10. The overall upconversion efficiency is limited by ba cktransfer processes from the Er3+ I-4(11/2) and S-4(3/2) states to Os4+ an d by the low Os4+ concentration. An upconversion-excitation mode for Er3+ a t the energy of the I-4(13/2)-->S-4(3/2) excited-state absorption is observ ed for the title compound.