Energy transfer and upconversion luminescence properties of Y2O3:Sm and Gd2O3:Sm phosphors

Y2O3:Sm and Gd2O3:Sm powder phosphors were prepared by carbonate coprecipitation method. The purified crystalline phases of Y2O3:Sm and Gd2O3:Sm were obtained at 600 deg. C, and the crystallinity increases with increase in annealing temperature. Both samples contain aggregated phosphor particles. An energy transfer (ET) from Y2O3 and Gd2O3 hosts to sm3+ has been observed, and the ET efficiency in the latter is higher than that in the former because an energy migration process like Gd3+-(Gd3+)n-Sm3+ has occurred in the latter. Furthermore, an upconversion luminescence from the 4G5/2 level of Sm3+ has been observed in both Y2O3 and Gd2O3 under the excitation of 936 nm infrared, whose mechanisms are proposed. Both the up and downconversion emission intensities of Sm3+ in Gd2O3 are stronger than those in Y2O3