Up-conversion luminescence properties of NaYTiO4: Yb3+, Er3+ under 1550 and 980 nm excitations

NaYTiO4:Yb3+, Er3+ phosphors with layered perovskite structure were prepared by a solid-state reaction method. The up-conversion luminescence (UCL) properties of the phosphors were studied under the 1550 and 980 nm excitations. The phosphors exhibited bright UCL. The observed emissions of the phosphors were similar and located at 510-580 nm and 635-698 nm, which correspond to the H-2(11/2)/S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) transitions of Er3+ ions, respectively. The dependence of UCL intensity on pump power indicates that the UCL was achieved via two- and three- absorption processes under the 980 and 1550 nm excitations, respectively. When excited by 1550 nm, the optimum doping concentration of Yb3+ ion was 12 %. Compared with the results of the phosphors excited at 980 nm, a significantly strengthened red emission and an Yb3+ concentration dependence of the red and green emission intensities were observed. These results can be attributed to the efficient I-4(9/2) -> I-4(11/2) multi-phonon relaxation and Er3+-> Yb3+-> Er3+ energy transfer process. The related UCL mechanisms and energy transfer processes were discussed in detail.