Gd2O2S:Yb,Er submicrospheres with multicolor upconversion fluorescence

Monodisperse hexagonal-phase Gd2O2S:Yb3+,Er3+ submicrospheres have been successfully prepared for the first time by means of a solvothermal method. The SEM and TEM results show that the spherical size is between 210-300 nm and the submicrospheres are of polycrystalline nature. Under the excitation of 980 nm, the bright green emission of the Gd2O2S:Er3+ at about 524 and 548 nm are assigned to the H-2(11/2)-> I-4(15/2) and S-4(3/2)-> I-4(15/2) transitions of the Er3+ ions, respectively. The incorporation of Yb3+ ions into the Gd2O2S:Er3+ leads to the decrease in the intensity ratio of the green luminescence to the red luminescence. The corresponding emission color can be tuned from green to yellow by varying the Yb3+ concentration. The analysis reveals that the two-photon absorption is mainly responsible for the upconversion luminescence in Gd2O2S:Yb3+,Er3+ submicrospheres.