UV luminescence of U4+ ions in LiYF4 single crystal: Observation of 5f16d1→5f2 transitions

Fluorescence studies, including lifetime measurements on LiYF4 single crystal doped with tetravalent uranium ions have been carried out at 77 and 300 K. The emphasis here has been on investigating spectral properties of U4+ ions on excitation with light corresponding to 5f2→5f16d1 absorption bands. These studies, for the first time, have led to the observation of intense luminescence at 300 K, in UV region having lifetime in nanosecond (ns) range. The observed fluorescence spectra have been interpreted as belonging to 5f16d1→5f2 inter-configuration transitions. These fluorescent transitions which are associated with small Stokes shift indicate that the electron cloud in excited 5f16d1 configuration has not extended appreciably relative to that of 5f2 configuration.