Vacuum ultraviolet 5d14f9-4f10 emission of Ho3+ ions in alkaline-earth fluorides

Time-resolved emission and excitation spectra as well as emission decay kinetics of CaF2, SrF2, BaF2 doped with HoF3 were investigated. Intensive emission bands near 168 nm, having long decay time, are caused by the spin-forbidden transitions from the 5d14f9 high-spin states to the ground 5I8 states of Ho3+ ions. Weak spin allowed 5d14f9(low-spin)-4f10 emission band at 158 nm was observed only in CaF2–Ho crystals. Spin allowed and spin-forbidden excitation bands were observed near 166 and 155 nm, respectively, in all studied crystals. Fast component of spin-forbidden emissions due to multiphonon relaxation to low-lying 4f10 Ho3+ level also was observed for all crystals.

► Time-resolved spectra of Ho3+ in CaF2, SrF2, BaF2 were studied in vacuum ultraviolet.
► Emission bands near 168 nm of Ho3+ ions are caused by the spin-forbidden transitions.
► Weak spin allowed 5d14f9-4f10 emission band at 158 nm was observed only in CaF2–Ho.
► Fast component of spin-forbidden emissions is due to multiphonon relaxation to 4f10 level.