Vacuum-ultraviolet spectroscopy and quantum cutting forGd3+inLiYF4

A systematic spectroscopic study of the ${4f}^7$ energy levels of ${\mathrm{Gd}}^{3+}$ in ${\mathrm{LiYF}}_4$ in the vacuum-ultraviolet spectral region $(50\mathrm{}000–70000{\mathrm{cm}}^{\mathrm{-}1})$ is reported. Using energy-level calculations, all observed spectral lines could be assigned to free-ion term symbols (including term symbols with unusually high $L$ and $J,$ e.g., a ${}^2{Q}_{23/2}$ level around $67000{\mathrm{cm}}^{\mathrm{-}1}$). From the ${}^6{G}_J$ levels around $50000{\mathrm{cm}}^{\mathrm{-}1}$ quantum cutting (or two-photon luminescence, photon-cascade emission) is observed: the emission of a red photon due to the ${}^6{G}_J{\to }^6{P}_J$ transition is followed by the emission of an ultraviolet photon due to the ${}^6{P}_J{\to }^8{S}_{7/2}$ transition.