Effect Of Different [Li]/[Nb] On The Defect Structure And Optical Properties Of Zn:Yb:Tm:LiNbO₃ Crystals

In this thesis,the Chuklaski method（also known as Tira method）is used to grow Zn:Yb:Tm:LiNbO₃crystals with different[Li]/[Nb]ratios.At the same time,there is no crack in the inner and surface of the crystal,and the optical uniformity and transparency are good.The concentration and effective separation coefficients of Zn²⁺,Tm³⁺and Yb³⁺ions in Zn:Yb:Tm:LiNbO₃crystals with different[Li]/[Nb]ratios were measured by inductively coupled plasma atomic emission spectrometry.The results show that the change of[Li]/[Nb]ratios in Zn:Yb:Tm:LiNbO₃crystal can affect the concentration of dopant ions and the effective separation coefficient of each ion.With the increase of[Li]/[Nb]ratios,the ion concentration and effective coagulation coefficient of Yb³⁺and Tm³⁺increased,while the ion concentration and effective coagulation coefficient of Zn²⁺decreased.The lattice constants and cell volumes of Zn:Yb:Tm:LiNbO₃with different[Li]/[Nb]ratios were measured by X-ray diffraction and phase analysis was performed.The results show that the crystal structure does not change and the doped ions enter the crystal in the way of substituting the lattice.Changing the[Li]/[Nb]ratios of the Zn:Yb:Tm:LiNbO₃crystal will lead to the change of the crystal volume,which first increases and then decreases.This is due to the difference in ionic radius and polarization ability between the doped ion and the ion at the original position,so that the cell volume of the crystal changes.It was found by the infrared transmission spectrum,it is found that changing the[Li]/[Nb]ratios in the crystal will lead to lithium ions entering the lattice preferentially occupying the antiposition niobium(Nb_Li⁴⁺)defect.With the increase of the[Li]/[Nb]ratios,the antiposition niobium(Nb_Li⁴⁺)defect in the crystal will be completely replaced,and the absorption peak position of the crystal will shift.It can be shown that the change of[Li]/[Nb]ratios will lead to the change of ion position in the lattice,and various types of defect groups will appear.The birefringent gradient method shows that the higher the[Li]/[Nb]ratio in Zn:Yb:Tm:Li Nb O3 crystal,the higher the refractive index distribution in all directions and the better the optical uniformity.The exposure energy threshold of Zn:Yb:Tm:LiNbO₃crystals is measured by the light scattering exposure energy flow threshold method,and the influence of different[Li]/[Nb]ratios on the exposure energy threshold of Zn:Yb:Tm:LiNbO₃crystals is discussed.It is found that the Zn:Yb:Tm:LiNbO₃crystals have good photodamage resistance,and the anti-exposure energy threshold can be effectively improved by increasing[Li]/[Nb]ratios.Finally,the upconversion luminescence mechanism is explained,and the influence of different[Li]/[Nb]ratios on the upconversion luminescence properties of Zn:Yb:Tm:LiNbO₃crystals is analyzed by upconversion luminescence spectra.The results show that the intensity of blue light at 475nm and red light emission at651nm are enhanced with the increase of[Li]/[Nb]ratios in Zn:Yb:Tm:LiNbO₃crystal.Improve the surrounding environment of the luminescent center ion,increase the energy transfer efficiency,and achieve the purpose of improving the upconversion luminescence intensity.