Comparison between the Photoluminescence Properties of LaPO₄:Tb,Ce Phosphor under 254nm Excitation and those under 365nm Excitation

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LaPO₄: Tb,Ce phosphors have been used for the green component of three-band emission type fluorescent lamps. We have confirmed that the emission intensity of Tb³⁺ under 254nm excitation is greatly enhanced by the energy transfer from Ce to Tb in the case of Ce co-doping, and the fluorescent intensity-temperature characteristics were also improved by substituting borate for a small part of phosphate, or by additive doping with thorium. In order to apply this phosphors to high pressure mercury lamps which operate at higher wall temperature and loading than low pressure mercury lamps, some characteristics of this phosphors under 365nm excitation were investigated. However, the green emission intensity under 365nm excitation was rather decreased by doping with cerium. The reason for this phenomenon could possibly be caused to energy transfer from Tb³⁺ to Ce³⁺, as excitation spectra of Tb³⁺ and emission spectra of Ce³⁺ overlap each other. Time-resolved spectra have been also observed under 365nm dye laser excitation. The ⁵D₃ --> ⁷F_j emission were found in highly Tb-doped LaPO₄:Tb,Ce phosphors, and new line emissions around 600nm which are considered to be originated by Ce²⁺ were found in (La,Ce,Th)(PO₄,BO₃):Tb phosphors under 365nm pulse excitation.