Study on up-conversion emissions of Yb3+/Tm3+ co-doped GdF3 and NaGdF4

The Yb3+/Tm3+ co-doped GdF3 and NaGdF4 samples were synthesized through a combination method of a co-precipitation and an argon atmosphere annealing procedures. X-ray diffraction analysis indicated that the Yb3+/Tm3+ co-doped GdF3 sample crystallized well and was orthorhombic phase, and the Yb3+/Tm3+ co-doped NaGdF4 sample was hexagonal phase. With a 980-nm semiconductor continuous wave laser diode as the excitation source, the up-conversion emission spectra of the two samples in the wavelength range of 240–510 nm were recorded. In the up-conversion emissions of the samples, Yb3+ transferred energies to Tm3+ resulting in their ultraviolet, violet, and blue up-conversion emissions. And, Tm3+ simultaneously transferred energies to Gd3+, which finally resulted in ultraviolet up-conversion emissions of Gd3+. The study on the excitation power dependence of up-conversion fluorescence intensity indicated that there were multi-photon (three-, four-, five-, and six-) processes in the up-conversion emissions of the samples. And the up-conversion emissions of Gd3+ and Tm3+ in the Yb3+/Tm3+ co-doped GdF3 and NaGdF4 samples were compared studied, too.