UP-CONVERSION LUMINESCENCE IN K2LAX5ER3+ (X=CL, BR)

Upconversion (UC) luminescence was observed in Er3+ (1%) doped K2LaCl5 and K2LaBr5 crystals. The two lattices exhibit distinctly different behavior. Upon I-4(9/2) excitation, the UC luminescence spectra of both the chloride and bromide are dominated by H-2(9/2) transitions at low temperature. At room temperature S-4(3/2) and H-2(11/2) become dominant. For I-4(11/2) excitation, the chloride and bromide show completely different luminescences. The F-4(7/2) luminescence dominates the bromide spectrum at all temperatures, but in the chloride, it is relatively unimportant. The differences are attributed to different F-4(7/2) --> H-2(11/2) multiphonon relaxation rates.