White upconversion emission in Yb3+/Tm3+/Ho3+ doped SrMoO4 nanocrystals by high excited state energy transfer

► The SrMoO4:Yb3+/Tm3+/Ho3+ nanocrystals were prepared by a sol-gel process. ► Excitation of the sample by 976 nm diode laser is studied. ► The UC mechanisms based on spectral, kinetic, and pump power dependence analyses were discussed. ► The bright white upconversion emission of the sample is due to the high excited state energy transfer.