Experimental investigation on the upconversion mechanism of 754 nm NIR luminescence of Ho3+/Yb3+:Y2O3, Gd2O3 under 976 nm diode laserexcitation

Upconversion (UC) spectra of Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics were obtained under the excitation of a 976 nm diode laser. Systematic experimental studies, including power dependence, luminescence lifetime, and the intensity ratio σ for the green to NIR emissions, were carried out in order to confirm the UC mechanism of Ho3+ ions. Our results demonstrated that the NIR emission was associated with the 5F4/5S2→5I7 transition of Ho3+ ions without the contribution of the 5I4→5I8 transition for Ho3+/Yb3+ codoped Y2O3 and Gd2O3 bulk ceramics. Additionally, population saturation in the 5I7 energy level had been observed in Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics. All experimental observations can be well explained by the steady-state rate equations.