Upon ultraviolet (UV) light excitation, an intense near-infrared (NIR) emission of Yb3+ (F25/2→F27/2) around 980 nm is observed in YVO4:Yb3+ phosphors. Owing to host absorption of YVO4, a broad excitation band ranging from 250 to 350 nm is recorded when the Yb3+ emission was monitored, which suggests an efficient energy transfer from host to Yb3+ ions. The Yb3+ concentration dependence of the visible vanadate emission as well as the Yb3+ emission is investigated. The decay curve of vanadate emission is measured under the excitation of a 266 nm pulsed laser. The decay time of the vanadate emission at 500 nm is remarkably reduced by introducing Yb3+ ions, further verifying that the energy transfer from the vanadate host to the Yb3+ ions is very efficient. Cooperative energy transfer (CET) is discussed as a possible mechanism for the NIR emission. The YVO4:Yb3+ phosphor can convert each UV photon into two NIR photons via CET, which has potential application in the high efficiency silicon-based solar cells.

Eu3+ doped YVO4 is excellent traditional red phosphor, but shifting its efficient excitation band to a longer wavelength is necessary for application in white light-emitting diodes, and is a big challenge that calls for good solution. Following the observation that cation substitution usually is an effective way to manipulate the band-gap of phosphors, we carried out ab initio calculation for the band-gap of pure and Bi3+ doped LnVO4 (Ln = Y, Lu, and Sc). The results show that the band-gap decreases with the cationic radius from Y3+ to Sc3+, and the doping of Bi3+ further decreases their band-gaps. The experimental results on the Eu3+ doped and Eu3+, Bi3+ co-doped LnVO4 (Ln = Y, Lu, and Sc) phosphors confirm this. In particular, the excitation of Eu3+ and Bi3+ co-doped ScVO4 is shifted to approach 400 nm, which fulfills the excitation requirement of near-ultraviolet-based white light-emitting diodes, and implies that Eu3+ and Bi3+ co-doped ScVO4 should be a promising candidate as red phosphor in white light-emitting diodes.