Vacuum ultraviolet and near-infrared excited luminescence properties of Ca3(PO4)2:RE3+, Na+ (RE=Tb, Yb, Er, Tm, and Ho)

Tb3+, Yb3+, Tm3+, Er3+, and Ho3+ doped Ca3(PO4)2 were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb3+-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb3+ content is comparable with that of the commercial Zn2SiO4:Mn2+ green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb3+, Tm3+, Er3+, and Ho3+ doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb3+–Ho3+, Yb3+–Er3+, and Yb3+–Tm3+ in Ca3(PO4)2, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb3+–Tm3+–Er3+–Ho3+ in Ca3(PO4)2, in which the cross-relaxation process between Er3+ and Tm3+, producing the 1D2–3F4 transition of Tm3+, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams.