Strong dependence of upconversion luminescence on doping concentration in holmium and ytterbium co-doped Y 2O 3 phosphor

Abstract

Under the excitation of 980 nm diode laser, intense green emission ( 5F 4+ 5S 2- 5I 8) of Ho 3+ was observed in Ho 3+ and Yb 3+ co-doped cubic Y 2O 3. The doping concentration and laser power dependence of the upconverted emission were studied. The decay curves of 5F 4+ 5S 2 emission of Ho 3+ under the excitation of 355 nm pulse laser were measured to investigate the energy transfer process between Ho 3+ and Yb 3+. The results indicated that two-photon process was responsible for the upconversion (UC) emission. The Ho 3+ concentration of 0.04 mol.% and the Yb 3+ concentration of 5 mol.% were determined to be the best value for the strongest Ho 3+ emission under the excitation of 980 nm light. The cross-relaxation between two neighboring Ho 3+ ions and the back energy transfer from Ho 3+ to Yb 3+ were important factors for determining the optimal doping concentration. This material was a promising candidate for the application in biomedical fluorescent labels for the intense green emission upon excitation of near-infrared (NIR) light.