Study on up-conversion emissions of Yb/Tm 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.