UP-CONVERSION LUMINESCENCE IN ER3+-DOPED RBGD2CL7 AND RBGD2BR7

Er3+-doped RbGd2Cl7 and RbGd2Br7 have been synthesized and grown as crystals using the Bridgman technique. Crystal absorption, upconversion luminescence, and Raman spectra are presented. Efficient infrared to visible upconversion is observed in both compounds at all temperatures between 10 and 295 K. Under I-4(9/2) excitation around 800 nm both compounds show similar upconversion spectra, whereas their behavior is distinctly different for 4I(11/2) excitation around 980 nm. The green light of the chloride originates from S-4(3/2) luminescence, whereas the bromide has a pure F-4(7/2) luminescence in the blue. This is due to the difference in the highest-energy vibration which is 264 and 180 cm(-1) for the chloride and bromide, respectively. Estimates of radiative and nonradiative rate constants are made for the various processes depopulating the F-4(7/2) state. Measured oscillator strengths of f-f transitions are compared with those determined from a Judd-Ofelt calculation. It is found that the F-4(7/2) --> I-4(15/2) is a potential laser transition in bromide lattices.