The role of sodium compound fluxes used to synthesize Gd2O2S:Tb3+ by sulfide fusion method

Different sodium compound fluxes were chosen to synthesize Gd2O2S:Tb3+ phosphor by the sulfide fusion method. X-ray diffraction, fluorescent spectrophotometer, field emission scanning electron microscope (FE-SEM), thermal gravimetric analyses and differential scanning calorimetry were used to analyze the influences of sodium compound fluxes on the phase formation, luminescence properties, morphology and reaction process of Gd2O2S:Tb3+. It was shown that the existence of Na2S2O3 and Na2Sx (x = 2 similar to 6) ensured the formation of Gd2O2S phase and improved the Tb3+ doping into substrate materials. The particle growth of phosphors was attributed to the effective flux agent of Na2S, and larger particles could be formed by adding Na2S. The grown particles presented a hexagonal shape, and larger particles were constructed by packing smaller ones along the c-axis direction. Furthermore, Gd2O2S:Tb3+ exhibited 544 nm emission peak due to the D-5(4) -> F-7(5) transition of Tb3+ when excited at 254 nm, and the luminescence intensity of it with the addition of Na2S2O3 was stronger than that prepared from other sodium compound fluxes including Na2Sx, Na2CO3, Na2SO3 and Na2S.