Facile synthesis of Gd2O2SO4:Tb and Gd2O2S:Tb green phosphor nanopowders of unimodal size distribution and photoluminescence

Abstract

Suppressing the crystallization and plate-like crystallite growth of RE2(OH)4SO4·2H2O compound by low-temperature (~4 °C) precipitation produced an amorphous RE2(OH)3.3(CO3)0.35SO4·2H2O precursor (RE = Gd1-xTbx) that can be decomposed to Gd2O2SO4:Tb and Gd2O2S:Tb green phosphor nanopowders of unimodal size distributions upon calcination in air at 1000 °C (average particle size ~156.9 nm) and in hydrogen at 800 °C (average particle size ~130.2 nm), respectively. The optimal RE3+ concentration for precursor synthesis was determined to be ~0.10 mol/L. Through detailed characterization by XRD, FTIR, DTA/TG, FE-SEM, TEM and particle sizing, the courses of phase/morphology evolution were clarified. Photoluminescence study found that the (Gd0.99Tb0.01)2O2SO4 and (Gd0.98Tb0.02)2O2S representative phosphors have quantum efficiencies of ~16.8% (λex = 275 nm) and 38.5% (λex = 286 nm), fluorescence lifetimes of ~3.70 and 1.75 ms and activation energies for thermal quenching of ~0.552 and 0.385 eV, respectively. The values are remarkably larger than those reported for Gd2O2S:Tb, which are considered to be due to higher purity, better crystallization and fewer luminescence-quenching defects of the product. Particularly, the (Gd0.99Tb0.01)2O2SO4 phosphor has negative thermal quenching up to ~150 °C and can retain over 85% of its room temperature emission intensity at 250 °C, which may enlighten its application in high-power LEDs.