INVESTIGATION OF INFRARED-TO-VISIBLE CONVERSION IN CUBIC CS2NAERCL6 CRYSTALS

Efficient conversion of infrared radiation centred at 1 mu m into visi ble luminescence has been observed in cubic Cs2NaErCl6 crystals in whi ch electric dipole transitions are forbidden by symmetry selection rul es. Luminescence originating from the F-4(9/2) and T-4(9/1) levels of Er3+ increases strongly with increasing temperature in the 100-300 K r egion whereas the S-4(3/2) luminescence appears to be independent of t emperature. Experimental results are found to be consistent with non-r esonant two-ion mechanisms involved in up-conversion and cross relaxat ion processes, the multiphonon decay being negligible.