Systematic synthesis of (Gd1-xLax)2O2SO4:Tb3+ and (Gd1-xLax)2O2S:Tb3+ nanophosphors for remarkably enhanced luminescence

Coprecipitation with rare-earth nitrate, ammonium sulfate, and ammonium hydroxide produced hydroxide-type amorphous precursors incorporating sulfate and carbonate anions, from which [(Gd1-xLax)(0.99)Tb-0.01](2)O2SO4 and [(Gd1-xLax)(0.99)Tb-0.01](2)O2S (x = 0, 0.15, 0.3, 0.5, 0.65, 0.8, and 1) were obtained as two series of nanophosphors by calcination at 950? in air and hydrogen, respectively. The detailed characterization by X-ray diffractometer, scanning electron microscopy/transmission electron microscopy, Brunauer-Emmett-Teller, and particle sizing confirmed that solid solutions were directly formed and that the products have small crystallite size, unimodal size distribution, and high specific surface area, revealing the advantages of the synthesis method. Photoluminescence study revealed that La3+ admixture may significantly improve the 545 nm main emission of Tb3+ for both the phosphor series. Furthermore, the 545 nm main emission of [(Gd1-xLax)(0.99)Tb-0.01](2)O2SO4 was identified to have an excellent thermal stability, which retained over 90% of its room-temperature intensity at 150? (no quenching for Gd2O2SO4:Tb3+). The two series of phosphors were comparatively studied for their excitation and luminescence performances, as a function of temperature and La3+ content, and the results were rationalized by considering bandgap, crystal structure, UV absorption, and the character of chemical bonds.