Low-temperature green synthesis of nanocrystalline La2O2S:Pr3+ powders and investigation of photoluminescence

Calcining an amorphous precursor in flowing hydrogen at 900 °C directly produced nanocrystalline La2O2S:Pr3+ powder (LOS:Pr3+; average size ∼35 nm) of a unimodal distribution of particle size (mean diameter ∼90 nm). The precursor, precipitated by titrating an aqueous solution of rare-earth nitrate and ammonium sulfate with ammonia water, was deduced to have an approximate composition of (La,Pr)2(OH)2.6(CO3)0.7SO4·2H2O. Aside from simplicity, the synthesis method reported herein has the obvious advantage of environmental friendliness, as it did not involve any harmful sulfidizing agent. The products were characterized in detail by XRD, FTIR, TG/DTA, and SEM/TEM to reveal the process of phase/morphology development and fine microstructure. Photoluminescence study found that the LOS:Pr3+ nanopowder exhibited strong luminescence at ∼508 nm (3P0,1 → 3H4 transition), with a fluorescence lifetime of ∼4.22 ± 0.03 μs, either through exciting the LOS host (∼263 nm, more efficient) or directly exciting the Pr3+ activator (∼304 nm), and retained ∼45% of its room-temperature intensity at 150 °C. Aside from phosphor application, the thus-synthesized powder would be useful for the fabrication of ceramic scintillators because of its nanosized crystallites and narrow distribution of particle size.