Study On The Upconversion White Light Properties Of Ho: Yb: Tm: LiNbO₃ Polycrystals

A series of Ho:Yb:Tm:LiNbO₃ polycrystals with various doping concentration were prepared by high-temperature solid method. First of all, the orthogonal experiment with 3 factors and 3 levels were carried out to select doped element concentration initially without considering the interaction of Ho³⁺, Yb³⁺, Tm³⁺, simultaneously, the results showed that the interactions between elements should not be ignored. On the basis of that, the orthogonal with 3 factors and 2 levels were carried out to investigate the interaction between elements and the influence to up-conversion luminescence properties. Finally, the single factor experiment was used to lay the foundation for the realization of up-conversion white light output in Ho: Yb: Tm: LiNbO₃ polycrystal systems.The up-conversion spectroscopies of Ho: Yb: Tm: LiNbO₃ polycrystals were tested to obtain the power-upconversion curves which were used to analyze the up-conversion mechanism of white light in Ho: Yb: Tm: LiNbO₃ polycrystal systems. According to the experimental results, it was speculated that the up-conversion process of red light and green light were single-photon process, and the up-conversion process of blue light was two-photon process in Ho: Yb: Tm: LiNbO₃ polycrystal system, since the saturation were occurred in the ⁵I₇ energy level of Ho³⁺ ions and the 3F4 energy level of Tm³⁺ ions, besides the cross-relaxation between Ho³⁺ and Tm³⁺.On the pre-trial basis, the bright up-conversion white light was received in Ho: Yb: Tm: LiNbO₃ polycrystal when Ho3 +, Yb3 +, Tm3 + doping concentrations were 0.1mol%, 2.0mol%, 0.2mol%, respectively, under 980nm laser excitation.The results of X-ray diffraction showed that there was no new phase appeared in Ho:Yb:Tm:LiNbO₃ polycrystals. All these polycrystals were still LiNbO₃ with trigonal system, but the lattice constants and cell volumes were changed slihtly. The results showed that the cell volumes of LiNbO₃ were decreased when doped with ions compared with undoped. And the occupying situations of doping ions were analyzed by UV - visible absorption spectra.