Visible spectra and fluorescence decay rates of a crystal and frozen solutions of uranyl nitrate

The absorption and fluorescence spectra of a UO2(NO3)2. 6H2O single crystal at 77 K agree with those reported previously. Analysis of the absorption spectrum yielded four electronic levels at 20590, 20625, 21474 and 23240 cm-1. The doublet at 20590 and 20625 cm-1 converged to form a singlet when the crystal was dissolved in water. This doublet was then interpreted as the result of Davydov splitting. The fluorescence decay rate of the doublet was measured between 77 and 300 K and its small thermal dependence explained by a theoretical model. The fluorescence and excitation spectra of frozen uranyl nitrate solutions at 77 K were recorded, and found to depend on molarity. This dependence was explained by assuming that there were three uranyl-nitrate-water species. The existence of these species is consistent with other measurements. (author)