6d5f configuration of U4+^{4+} doped into LiYF4^4 crystal

Observation of luminescence due to 6d5f5f2 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+ 6d5f5f2 luminescence are similar to those of 5d4f4f2 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 df transitions

Low-temperature high-resolution VUV spectroscopy of Ce3+ doped LiYF4, LiLuF4 and LuF3 crystals

RadiochFor LiYF4:Ce3+, LiLuF4:Ce3+ and LuF3:Ce3+ crystals UV/visible emission and time-resolved VUV/UV excitation spectra were recorded at liquid helium temperature with spectral resolution of 0.1 nm for excitation spectra and better than 0.3 nm for emission spectra. Well resolved fine structures due to zero-phonon lines were clearly observed in both excitation and emission spectra for LiYF4:Ce3+ and LiLuF4:Ce3+. For LuF3:Ce3+ crystal no fine structure was detected in the spectra even at the highest spectral resolution. Under the host excitation, the fine structure for high-energy emission band of Ce3+ (5d-F-2(5/2)) in LiLuF4:Ce3+ becomes well pronounced because of weaker reabsorption effect, as compared to Ce3+ 4f-5d absorption, due to small penetration depth for exciting radiation. As a result the crystal-field splitting for F-2(7/2) and F-2(5/2) levels of Ce3+ in LiLuF4 crystal was measured. First observation of zero-phonon lines at similar to81,550 and similar to82,900 cm(-1) as well as vibronic side bands due to interconfigurational 4f(14)-4f(13)5d transitions in Lu3+ is reported for excitation spectrum of LiLuF4:Ce3+