Green upconversion luminescence in Yb3+/Er3+ co-doped ALn(MoO4)2 (A = Li, Na and K; Ln = La, Gd and Y)

Yb3+ and Er3+ co-doped ALn(MoO4)2 (A = Li, Na and K; Ln = La, Gd and Y) phosphors were synthesized by sol–gel method. The structures and the phase purities of the samples were characterized by X-ray diffraction (XRD). The shapes and size distribution of the phosphor particles were also investigated by the field emission scanning electron microscopy (FE-SEM). The phosphors showed intense green emission peaked at 530 and 552 nm due to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ under the excitation of a 980 nm laser diode. The dependences of their UC luminescence properties on the hosts, the concentration of the dopants and annealing temperature were investigated. The phosphor showed the brightest green emission as the concentration of Er3+ fixed at 0.5 mol% and the annealing temperature is 800 °C. In the range from 5 to 20 mol%, the more Yb3+ was doped, the more intense UC luminescence can be achieved. The UC excitation mechanism for green emission of Er3+ was also investigated based on the power dependence of UC luminescence intensity.

► Green upconversion phosphors ALn(MoO4)2: Er3+, Yb3+ (A = Li, Na, K; Ln = La, Gd, Y) were prepared.
► Pure phase obtained at 600 °C and the UC luminescent properties were investigated.
► Mechanism of up-conversion were discussed.