Titrating the aqueous solution of equimolar RE(NO3)(3) and (NH4)(2)SO4 with NH4OH to pH similar to 9 at similar to 4 degrees C produced an amorphous precursor that yielded phase-pure and well-dispersed RE2O2S nanopowder (RE = Gd0.99Tb0.01; GOS:Tb) via a RE2O2SO4 intermediate upon annealing in H-2. The powders calcined at the typical temperatures of 700/1200 degrees C exhibited unimodal size distributions and have the average crystallize sizes of similar to 17/55nm, average particle sizes of similar to 284/420nm, and specific surface areas of similar to 14.62/4.53m(2)/g (equivalent particle sizes: similar to 56/180nm). The 1200 degrees C product exhibited sharp green luminescence at similar to 544nm (FWHM=2.3nm; (ex)=275nm), with an absolute quantum yield of similar to 24.8% and a fluorescence lifetime of similar to 1.34ms at room temperature. It was also shown that the powder possesses favorable thermal stability (the activation energy for thermal quenching of luminescence similar to 0.305eV) and is stable under electron beam irradiation up to 7kV and 50A. The synthetic technique has the advantages of scalability and favorable dispersion and high chemical/phase purity for GOS powder, which may allow the sintering of scintillation ceramics at lower temperatures.