Effect of temperature on up-conversion phenomena in Gd3(Al,Ga)5O12 crystals co-doped with Yb3+ and Tm3+

Single crystals of Gd-3(Al,Ga)(5)O-12 with intentional stoichiometry Gd3Ga2.5Al2.5O12 doped with 1%Tm3+ + x% Yb3+; (x = 1, 3, 5); were grown by the Czochralski method. Spectra and intensities of up-converted luminescence excited at 975 nm or 803 nm were measured as a function of temperature within 295 K-775 K region. It was found that for the two excitation wavelengths the growth of temperature brings about a decrease of an upconverted blue luminescence intensity. Thermally enhanced growth of nonradiative relaxation rates for excited states involved in the up-conversion process was determined based on an analysis of respective luminescence decay curves. Temperature-dependent change of fluorescence intensity ratio (FIR) for the F-3(3,2 )-H- 3(6)/H-3(4) - H-3(6) up-converted bands was observed and resulting absolute temperature sensitivity of 0.058 K-1 was found for GAGG:1%Tm,3%Yb at 725 K.