Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles

Cubic and/or monoclinic Y2O3:Eu3+ nanoparticles (10-50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700-1300 degrees C for 10 h) as-prepared, initially monoclinic Y2O3:Eu3+ nanoparticles resulting in larger 0.025-1 mu m, cubic Y2O3:Eu3+. The influence of europium (Eu3+) content (1-10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y2O3:Eu3+ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y2O3 particles at 900, 1100 and 1300 degrees C for 10 h, the PL intensity increased as particle size increased and finally (at 1300 degrees C) showed similar PL intensity as that of commercially available, bulk Y2O3:Eu3+ (5 pm particle size). Eu doping stabilized the monoclinic Y2O3 and shifted the monoclinic to cubic transition towards higher temperatures.