Luminescent properties of Pr3+-sensitized LaPO4:Gd3+ ultraviolet-B phosphor under vacuum-ultraviolet light excitation

Luminescent properties of Pr3+-sensitized LaPO4:Gd3+ under vacuum-ultraviolet (vuv) light excitation have been investigated. The energy transfer probably occurs from the 5d levels in Pr3+ ions to Gd3+ ions under 172 nm light excitation. LaPO4:Gd3+,Pr3+ shows efficient ultraviolet-B (uv-B) emission at 312 nm, whose peak intensity reaches its maximum at Gd=35 mol % and Pr=5 mol %. (La0.65Gd0.35)(0.95)Pr0.05PO4 is about 1.6 times higher than a typical uv-B phosphor for vuv lamp, Y0.75Gd0.25Al3(BO3)(4), in Gd3+-emission intensity under 172 nm light excitation. This result implies that the Pr3+-sensitized LaPO4:Gd3+ is a candidate of uv-B phosphors for xenon-excimer discharge vuv lamps. In order to evaluate the effect of the narrow-band uv-B emission by LaPO4:Gd3+,Pr3+ phosphor, irradiation test on DNA was performed. The irradiation damage of pUC 18 DNA by the narrow-band uv-B light from the LaPO4:Gd3+,Pr3+ phosphor is in the same magnitude as that by uv-A light from a filtered Hg lamp, even though the uv-B lamp is higher than the uv-A lamp in power density and photon energy.