Study On The Photo-refractive Properties Of Sc And Mn And Fe Doped Lithium Niobate Crystal

Sc:Mn:Fe:LiNbO₃ crystal series are grown by Czochralski method at thefirst time, and the crystals have no macroscopic defect and exhibit good opticalhomogeneity. Appropriate parameters(temperature gradient, pulling speed androtating speed) are chosen during the crystal growth process to maintain the flatsolid-liquid interface and decrease the component asymmetry furthest, which isorigined from the solute segregation. The location of the doped ions in the crystalwas analyzed by measuring X-ray power diffraction, infrared spectra and Ultra-visible spectra. The photo-refractive and photo-refractive resistant properties ofthe crystals were measured and the mechanism of the influence of the doped ionswas investigated. The recording experiments were carried out, too.The results of X-ray power diffraction, infrared spectra and Ultra-visiblespectra showed that there is no new phase appeared in the doped LiNbO₃ crystals.The crystals hold the same lattice structure as the pure congruent lithium niobatecrystal, but the lattice constants have comparable change. The doped ions canonly replace Li⁺, NbLi⁴⁺ or Nb⁵⁺. Mn³⁺ and Fe³⁺ locate normal Li⁺ sites and thenNb⁵⁺ sites when Sc³⁺ concentration is up to the threshold in the LiNbO₃ crystal.Sc ions entering LiNbO₃ crystal firstly substitute NbLi⁴⁺ and then occupiednormal Li⁺ and Nb⁵⁺ sites when their concentration is up to the threshold.O-H absoption peak of Sc(3mol%):Mn:Fe:LiNbO₃ crystal shifts to 3505 cm-1, compared with that of other crystals doped with lower Sc concentration 3483cm-1, which indicates that Sc doping concentration of 3mol% is over thethreshold. With the increase of Sc doping amount, the absorption edge inultraviolet-visible absorption spectra of Sc:Mn:Fe:LiNbO₃ crystal shifts the violetand then inversely to the red when Sc doping concentration is up to the threshold.The photo-refractive and photo-refractive resistance properties are measured by two wave coupling and facula distortion method, respectively. The refractiveindex change maximum and dynamic range of crystals decrease, but responsespeed and photorefractive sensitivity increase with the increase of Sc dopingconcentration in raw material. When Sc ions concentration is up to the threshold,the optical intensity threshold improves two orders of magnitude. And with theLi/Nb ratio increased,the refractive index change maximum and dynamic range ofcrystals decrease, but response speed and photorefractive sensitivity increase. Themachnism is discussed combining the location analysis of doping ions in LiNbO₃crystal.The holographic storage experiment was carried out by using theSc:Mn:Fe:LiNbO₃ crystals as storage medium. the quality of the output picturestored in the(3mol%)Sc:Mn:Fe:LiNbO₃ crystal was higher than the other LiNbO₃crystals. The results indicated that the photorefractive effect can be affected bydoping the Sc ions to the crystals and changing the Li/Nb ratio. It is helpful forimproving the application in holographic storage.