Study On Defective Structure And Optical Properties Of Ruthenium-Ferrum Series Co-doped Lithium Niobate

Volume holographic storage technology is an excellent technical means suitable for large-scale data storage.Nowadays,it is playing an increasingly important role.After years of development,lithium niobate crystals have become the most commonly used holographic storage material,which depends on their unique photo-refractive performance.In practical application,in order to improve their holographic storage performance and photo-damage resistance,lithium niobate doping modification is necessary.After the analysis,two photo-refractive sensitive ions,Ru⁴⁺and Fe³⁺are selected.They can be doped into Li Nb O₃crystal as photo-refractive centers to improve the holographic storage performance of lithium niobate.Zinc ions and indium ions are selected as the third doping elements respectively to improve the photo-damage resistance.In order to explore the effect of[Li]/[Nb]and the concentration change of dope ions on crystal defect structure and optical properties,a series of Zn:Ru:Fe:Li Nb O₃crystals with different[Li]/[Nb]（0.946,1.05,1.20,1.38）and In:Ru:Fe:Li Nb O₃crystals with different In³⁺concentrations（0,1mol%,3mol%,5mol%）were grown by the Czochralski method.The concentration of doped ions Zn2+、Ru4+and Fe3+in Zn:Ru:Fe:Li Nb O₃crystal,and Zn²⁺、Ru⁴⁺and Fe³⁺in In:Ru:Fe:Li Nb O₃crystal is measured by inductively coupled plasma atomic emission spectrum（ICP-AES）method,and the effective segregation coefficient of each doped element is calculated.The experiments show that the change of[Li]/[Nb]and the concentration of In³⁺ions will affect the occupation of doped ions in the crystal,which leads to the change of the effective segregation coefficient of doped ions.In Zn:Ru:Fe:Li Nb O₃,the increase of[Li]/[Nb]leads to the decrease of the effective segregation coefficient of Zn²⁺ions.Thus the effective segregation coefficient of Ru4+and Fe3+ions increases.In In:Ru:Fe:Li Nb O₃crystal,the effective segregation coefficient of In³⁺ions increases with its doping concentration,resulting in reducing the effective In³⁺coefficient of Ru4+and Fe3+ions.The structure of crystal samples was analyzed by X-ray diffraction spectrum（XRD）method and the crystal cell constant was measured.It is found that there was no new diffraction peak compared with the pure lithium niobate,and the doped elements enter the crystal cell in terms of ion substitution.Due to the change of doped concentration of ions in the crystal and the different ion radius and polarization ability of doped ions,the change of[Li]/[Nb]and the change of In3+concentration both make the crystal cell size expand first and then shrink.At the same time,the molecular groups in the crystal are analyzed by infrared spectrum.The internal defect structure of different lithium-niobium ratio and In3+ion concentration is studied.And the change of the defect structure in the crystal is analyzed when the parameters are changed.Finally,the optical property of the crystal is investigated.The photo-refractive performance of each crystal sample was analyzed by a two-wavelength non-volatile holographic storage test.Through the analysis and calculation of each measured parameter,crystal samples with the best optical performance were determined.The experiment show that Zn:Ru:Fe:Li Nb O₃has the shortest writing time and maximum erase time at the[Li]/[Nb]of 1.38.The diffraction efficiency,sensitivity,and dynamic range were the highest among the four samples.The holographic storage performance of sample Zn Rn Fe_1.38is the best.In:Ru:Fe:Li Nb O₃holographic storage performance is best at an indium ion concentration of 5mol%.Specifically,it has the shortest grating writing time,the longest erasure time,and the high diffraction efficiency,sensitivity and dynamic range.