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 ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_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 ⁴I_9/2 → ⁴I_11/2 multi-phonon relaxation and Er³⁺→Yb³⁺→Er³⁺ energy transfer process. The related UCL mechanisms and energy transfer processes were discussed in detail.