Description:
Abstract The effect of high density excitation on the phosphorescence spectra and their decay curves of crystalline uranyl(VI)nitrate hexahydrate, uranyl(VI)acetate dihydrate, and zinc uranyl(VI)acetate heptahydrate was studied using a nitrogen laser as the exciting light source. The relative emission intensity of the spectra in the shorter wavelengths decreased and the vibrational structure became broader at higher density excitations; these changes were attributed to the saturation in excitation and to the temperature increase in the irradiated volume of the sample crystal caused by the heat released in the radiationless decay process. A decrease in the decay time was also observed at high density excitations; this shortening was attributed to bimolecular quenching of triplet excitons in the crystal. The rate constant for this process in crystalline uranyl nitrate hexahydrate was measured at several temperatures between 77 and 295K; it was 2.6×10−13 cm3 s−1 at 295K for example. From this rate constant the hopping rate for a triplet exciton in crystalline uranyl nitrate hexahydrate was obtained: 4.3×108 cm3 s−1 at 295K. The activation energy for the exciton migration was found to be 320 cm−1.