| Rare earth doped optical materials have become a research hotspot, because up-conversion fluorescence technology using rare-earth ions as luminescence centers has great application potentials and prospects for development, which leads to the exploration of new materials with higher photoluminescence properties based on the traditional optical materials. The object of this study is to search doped lithium niobate (LiNbO3) crystals with traditional metal ions and different rare earth ions. The doping effects from different elements and concentrations were systematically analyzed and compared. Variations in defect structure and optical characteristics after doping with metal elements and rare earth elements have been revealed. This study may provide abundant theoretical basis for future research, and experimental guidance for the preparation of laser crystals.In this dissertation, LiNbO3crystals were doped with rare earth ions (Ho and Nd) and metal ions (Mg, Yb and In). Defect structures of doped LiNbO3crystals were studied by X-ray diffraction, infrared absorption spectra, and UV absorption spectra. The up-conversion fluorescence machanism was investigated by measuring the up-conversion fluorescence, power curve, and J-O theoretical calculation. The resistance ability for optical damage of doped LiNbO3crystals was also measured.Different concentrations of Ho3+/Nd3+were doped into the LiNbO3crystals, and Ho3+/Nd3+ions preferably occupied the anti-Nb sites in the defect structure. When the concentration of Ho3+/Nd3+ions reaches or exceeds a threshold value, they will gradually replace the normal Nb and Li sites. The up-conversion luminescence intensity firstly increases with increasing Ho3+/Nd3+concentrations, while starts to reduce when the concentration reaches a threshold value.Different concentrations of Mg2+ions, which can enhance the optical damage resistance ability, were doped into the Ho/Nd:LiNbO3crystals. With a concentration of Mg2+ions below the threshold value (5mol%), Ho3+/Nd3+preferentially occupy the Li sites, and partially the Nb sites, leading to the formation of isolated defect centers and defect center. However, when Mg2+concentration reaches or exceeds the threshold value, Ho3+/Nd3+defect center will be dissociated rapidly, and even disappear. Due to the influence of defect center concentration, the up-conversion luminescence intensity of Ho/Nd:LiNbO3crystals firstly increases with increasing Mg2+concentration, and then decreases when the Mg2+concentration reaches a threshold value. Importantly, the optical damage resistance performance can be increased by two orders of magnitude compared to the Ho/Nd:LiNbO3crystals without Mg2+doping. Yb3+does not participate in the luminescence process, but it is an excellent sensitizer. Different concentrations of Yb3+ions were doped into the Ho/Nd:LiNbO3crystals, and Yb3+and Ho3+/Nd3+preferentially occupy the anti-Nb sites. This synergetic doping can promote the formation of defect center., The up-conversion luminescence increases with increasing Yb3+concentration.Different concentrations of In3+ions (which has a lower threshold concentration than Mg2+) and a fixed concentration of Yb3+were simoutaneously doped into the Ho/Nd:LiNbO3crystals, and the internal defect structure of each crystal was further analyzed. Before In3+reaches the threshold value, higher In3+concentration can promote the formation of defect center. When the concentration of In3+ions reaches or exceeds the threshold value, the beam defect structure can be dissociated. Through power curve tests, it is determined that the up-conversion fluorescence of doped LiNbO3crystals originates from a two-photon process, where green light is stronger and red light is weaker. Optical damage resistance ability is significantly enhanced with increase in In3+concentration, while the intensity of upconversion luminescence is somehow weakened. |
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