Yellow-green upconversion photoluminescence in Yb3+, Ho3+ co-doped NaLa(MoO4)2 phosphor

Upconversion (UC) properties of Yb3+, Ho3+ co-doped NaLa(MoO4)2 phosphors, synthesized by solid state reaction, were investigated in detail under the excitation of 970 nm laser diode. The UC luminescence consists of green emission assigned to the 4F4/5S2 → 5I8 (Ho3+) transition and red emission assigned to the 5F5 → 5I8 (Ho3+) transition. The light color of the UC luminescence is dependent on the Yb3+ concentration. UC mechanisms were analyzed based on the pump power dependence. The energy transfer efficiency between Yb3+ and Ho3+ was also investigated and the maximum efficiency of 72% was achieved when the Yb3+ concentration increasing up to 20%. Results have shown that the Yb3+, Ho3+ co-doped NaLa(MoO4)2 powder has a potential as a yellow-green UC phosphor for lighting and signal indication.