Polyol synthesis of YVO₄:Bi³⁺,Eu³⁺ nanophosphors and effect of silica coating on their photoluminescence properties

YVO₄:Bi³⁺,Eu³⁺ nanophosphor is prepared from sodium orthovanadate and nitrates of yttrium, bismuth, and europium in a polyol solvent of diethylene glycol at 160°C. The photoluminescence (PL) intensity of the nanophosphor is enhanced by a factor of 3.3 after silica coating via reverse micelle method. The gradual increase in the PL intensity is observed under the continuous excitation irrespective of silica coating. This increase in the PL intensity is attributed to the photooxidation of V⁴⁺ to V⁵⁺, as confirmed by electron spin resonance spectroscopy. Finally, a highly luminescent and photostable nanophosphor can be prepared by combination of photooxidation pre-treatment and silica coating.