Near-infrared Downconversion in LuPO4: Tm3+, Yb3+ Phosphors.

Tm3+ and Yb3+ codoped LuPO4 phosphors were synthesized by the reverse-strike co-precipitation method. The obtained LuPO4:Tm3+,Yb3+ phosphors were characterized by X-ray diffraction (XRD), diffuse reflectance spectra, photoluminescence (PL) spectra, and decay lifetime to understand the observed near-infrared downconversion (DC) phenomena. The XRD results show that all the prepared phosphors can be readily indexed to the pure tetragonal phase of LuPO4 and exhibit good crystallinity. The experimental results showed that the strong visible emission around 649 nm from Tm3+(1G4 --> 3F4) and near-infrared (NIR) emission around 1003 nm from Yb3+(2F5/2 --> 2F7/2) of LuPO4:Tm3+,Yb3+ phosphors were observed under 468 nm excitation, respectively. The Yb3+ concentration dependence of luminescent properties and lifetimes of both the visible and NIR emissions have also been investigated. The quenching concentration of Yb3+ ions approaches 30 mol%. The DC mechanism is also discussed in detail.