Effects of the homogeneous Bi doping process on photoluminescence properties of YVO4:Bi,Eu nanophosphor

YVO₄:Bi³⁺,Eu³⁺ nanophosphors at a high Bi³⁺ concentration of 15 at% are synthesized from a Bi³⁺ source, nitrates of yttrium and europium(III), and sodium orthovanadate(V) by a low-temperature aqueous precipitation in the presence of citrate ions. When an ethylene glycol solution of bismuth(III) nitrate is used as a Bi³⁺ source, YVO₄:Bi³⁺,Eu³⁺ nanophosphors of ∼20 nm in size crystallize during aging at 85 °C without any by-products where the contents of Bi³⁺ and Eu³⁺ incorporated into crystalline YVO₄ are close to the respective nominal contents, as confirmed by transmission electron microscopy, X-ray diffractometry and X-ray fluorescent analysis. These nanophosphors show red emission corresponding to the f-f transition of Eu³⁺ under the excitation of Bi³⁺-V⁵⁺ charge transfer. When aging is continued after the completion of the crystallization, the photoluminescence intensity of nanophosphors reaches the constant value. This is the improved behavior in comparison to our previous work, where the photoluminescence intensity decreases after the prolonged aging because of the inhomogeneous doping of Bi³⁺ ions, and hence the concentration quenching.