Abstract
Photoluminescence properties of - or -doped under UV and vacuum ultraviolet (VUV) excitations are investigated. A broad band with the maximum at 172 nm observed in the VUV excitation spectra of ( and ) is assigned to the host absorption. The excitation intensity ratio of charge transfer to that of the intraconfigurational 4f–4f transitions of and is rather low in , showing that energy transfers efficiently from to and to and the covalency of is increased due to the existence of F. The energy-transfer process in upon host excitation and excitation is explained by a quantum cutting process. The quantum cutting involves a cross relaxation process between two neighboring and direct energy transfer between and or and , depending on the excitation wavelength.
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