Tunable luminescence and near white-light emission of YPO^sub 4^:Eu^sup 3+^,Tb^sup 3+^,Tm^sup 3+^ phosphors

Tb3+, Eu3+, Tm3+ tri-doped YPO4 powders were synthesized by high-temperature solid-state reaction in order to realize a white-light-emitting single-phase phosphor. Their photoluminescence spectra and time decay curves were measured. Nearly white luminescence was observed under 362 nm excitation for the sample doped with 2% Eu3+, 5% Tb3+ and 2% Tm3+, with chromaticity coordinates (x = 0.315, y = 0.273) rather close to those of the standard white illuminant D65 (x = 0.313, y = 0.329). In order to explore the effect of the Tm3+ ions on the emission properties, a series of experiments on YPO4 co-doped with Tm3+, Tb3+ and Tm3+, Eu3+ has been carried out, demonstrating that the interactions between the active ions are weak in the former case, whereas in the latter a significant quenching of the Eu3+ emission with increasing Tm3+ concentration has been observed and interpreted on the basis of a suitable cross-relaxation process.