Upconverted VUV luminescence of Nd3+ and Er3+ doped into LiYF4 crystals under XeF-laser excitation

The upconverted VUV (185 nm) and UV (230 and 260 nm) luminescence due to 5d–4f radiative transitions in Nd3+ ions doped into a LiYF4 crystal has been obtained under excitation by 351/353 nm radiation from a XeF excimer laser. The maximum upconversion efficiency, defined as the ratio of intensity for 5d–4f luminescence to overall intensity for 5d–4f and 4f–4f luminescence from the 4D3/2 Nd3+ level, has been estimated to be about 70% under optimal focusing conditions for XeF laser radiation. A redistribution of intensity between three main components of 5d–4f Nd3+ luminescence is observed under changing the excitation power density, which favors the most long-wavelength band (260 nm) at higher excitation density level. The effect is interpreted as being due to excited state absorption of radiation emitted. The upconverted VUV and UV luminescence from the high-lying 2F(2)7/2 4f level of Er3+ doped into a LiYF4 crystal has also been obtained under XeF-laser excitation the most intense line being at 280 nm from the spin-allowed transition to the 2H(2)11/2 4f level of Er3+, but the efficiency of upconversion for Er3+ emission is low, less than 5%.