Hydrothermal synthesis and the enhanced blue upconversion luminescence of NaYF4:Nd3+,Tm3+,Yb3+

Nd3+, Tm3+ and Yb3+ co-doped NaYF4 upconversion (UC) material was synthesized by the hydrothermal method. The structure of the sample was characterized by the X-ray diffraction, and its UC luminescence properties were investigated in detail. Under the 980 nm semiconductor laser excitation, its UC spectra exhibited distinct emission peaks at 451 nm, 475 nm and 646 nm respectively. On the basis of the comparison of UC spectra between NaYF4:Nd3+,Tm3+,Yb3+ and NaYF4:Tm3+,Yb3+, it was indicated that the existence of Nd3+ ion enhanced the blue emission intensity. The law of luminescence intensity versus pump power proved that the blue emission at 475 nm, and the red emission at 646 nm were the two-photon processes, while the blue emission at 451 nm was a three-photon process.