Upconversion luminescence in Er-doped γ-AlON ceramic phosphors

γ-AlON:Er3+ phosphors with different Er3+ concentration for upconversion luminescence were prepared by a combination of carbothermal reduction and nitridation and solid-state synthesis methods. The effect of Er3+ content on emission spectra was investigated. Under the excitation of 980 nm diode laser, green emission centered at 548 nm and red emission centered at 666 nm were observed, which are ascribed to the transition of 4S3/2/2H11/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions, respectively. The pump power dependence indicates a two-photon process involved in the upconversion luminescence. The ratio of red emission relative to green emission was enhanced with the increase in Er3+ concentration. The possible mechanisms were discussed.