6d5f configuration of U4+ doped into LiYF4 crystal

Observation of luminescence due to 6d5f→5f2 electronic interconfigurational transitions in U4+ doped into LiYF4 crystal is reported. This luminescence originating from the lowest level of the 6d5f electronic configuration and terminating on different levels of the 5f2 electronic configuration of U4+ consists of four relatively wide emission bands in the UV spectral range (240–370 nm), characterised by a luminescence decay time of 15 ns at 300 K. Excitation spectrum of U4+ 6d5f→5f2 luminescence has a threshold at ∼250 nm and at least nine bands in the transparency region of the host. The properties of U4+ 6d5f→5f2 luminescence are similar to those of 5d4f→4f2 luminescence of Pr3+ ion embedded into crystals where the lowest 5d4f level of Pr3+ lies below the 1S0 (4f2) level. U4+-doped fluoride crystals can be considered as promising materials for tuneable UV solid-state lasers based on d↔f transitions.