Upconversion Luminescent Properties of YVO4:Tm3+,Ho3+,Yb3+

YVO4 co-doped with Tm3+/Ho3+/Yb3+ were synthesized by the high temperature solid state method and the optical properties of phosphors were characterized. Intense visible emissions centered at around 475, 541 and 649 nm, originated from the transitions of Tm3+:(1)G(4)-> H-3(6), Ho3+:S-5(2)/F-5(4)-> I-5(8), Tm3+:(1)G(4)-> F-3(4) and Ho3+:F-5(5)-> I-5(8), respectively, have been observed in samples upon excitation with a 980 nm laser diode, and the involved mechanisms have been explained.