One-step Ar/O2 thermal plasma processing of Y2O3:Eu3+ red phosphors: Phase structure, photoluminescent properties, and the effects of Sc3+ codoping

(Y0.95Eu0.05)2O3 red phosphors are synthesized in one step via Ar/O2 thermal plasma oxidation of atomized alcohol solutions of the component nitrates. Phase structure analysis found the direct products to be mixtures of a cubic and monoclinic phases, and the powder collected from the wall part of the plasma reactor as well as the finer portion of the total powder have significantly higher monoclinic contents (∼55 and 71 wt%, respectively). An almost pure-cubic structured phosphor powder can be converted from the phase mixture by annealing at a minimum temperature of 900 °C for 12 h, but at the expenses of significant coarsening/sintering of the nano-sized particles. It was first shown that codoping with 20 at% of Sc3+ may effectively retard crystallization of the undesired monoclinic phase and thus yield phosphor powders of high specific surface area (∼21.7 m2/g) and significantly improved 611-nm red emission. Formation mechanism of the monoclinic phase and the effects of Sc3+ codoping on phase structure and luminescence properties were discussed.