Effect Of Different Valency Optical Damage Resistant Ions On Defect And Optical Properties Of Er:LiNbO₃Crystals

Er-doped wavelength amplifiers （EDWAs） will be one of the key componentsof futher microphotonic systems, and Er:LiNbO₃crystals, used as the host materialsfor EDWAs, have excellent advantages such as the high stabilization and integration.Furthermore, Er:LiNbO₃crystals could combine the laser performances of Er³⁺ionwith the nonlinear characteristics presented by LiNbO₃crystal. Er:LiNbO₃emits1.54μm near infrared emission, which corresponds to the standard communication“window” wavelength. Howerve, the practical applications of Er:LiNbO₃crystalsare limited by the optical damage effect. Different valence Zn²⁺, In³⁺and Zr⁴⁺ionsare chosen to enhance the optical damage of LiNbO₃crystals. We performinvestigations on the effect of different valence optical damage resistant ions on thedefect structure and optical characteristics of Er:LiNbO₃crystals, which provide thetheoretical and experimental direction for us to obtain the high efficient1.54μmnear infrared emission.The geometry structure of LiNbO₃crystals doped with Zn²⁺, In³⁺and Zr⁴⁺ionsare calculated by the first principle theory, which shows that Zn²⁺, In³⁺and Zr⁴⁺ionsoccupy Li sites firstly. The stuies on the stability of Zn²⁺, In³⁺and Zr⁴⁺ionsoccupied Li sites show that Zn²⁺ions will push Er³⁺ions into Nb sites, and the Er³⁺clusters sites are formed in Er:LiNbO₃crystals, and In³⁺ions have little effect on theoccupancy of Er³⁺ions, and the low stability of Zr⁴⁺ion makes Er³⁺ions stilloccupy Li sites.The Er:LiNbO₃crystals are grown by Czochraski method. The defect structureof Er:LiNbO₃with different Er³⁺ion concentration, as well as the near infraredemission, upconversion emission and mechanism under different excitationwavelength are studied. It has been proposed that the formation of Er³⁺cluster sitescould increase the rate of cross relaxation processes. Under980nm excitation, Er³⁺cluster sites will suppress the1.54μm near infrared emission. Studies on the effectof [Li]/[Nb] ratio （is equal to0.94,1and1.25, respectively） on the defect structureand optical characteristics of Er:LiNbO₃crystals show that as for [Li]/[Nb]=1, theEr³⁺cluster sites are dissociated and the strongest1.54μm emission is observed inEr:LiNbO₃crystal.The studies on the defect structure and optical characteristics of Er³⁺（3mol%）:LiNbO₃crystals doped with3,6and7mol%Zn²⁺ions show that thethreshold concentration of Zn²⁺ion is not affected by Er³⁺ions in Zn/Er:LiNbO₃crystal. When the concentration of Zn²⁺ions is lower than its threshold, the Er³⁺cluster sites are dissociated by Zn²⁺ions, which results in the enhancement of1.54 μm near infrared emission. When the concentration of Zn²⁺ions is higher than itsthreshold, the reformantion of Er³⁺cluster sites are observed, which decreases the1.54μm near infrared emission. Combined the first principle theory with the relationbetween the occupancy and optical characteristics of Er³⁺ions, the Zn/Er:LiNbO₃crystals with the3/1.5,6/1and7/1.5mol ratio of Zn²⁺/Er³⁺are grown. The strongest1.54μm emission is found in Zn/Er （6mol%/1mol%）:LiNbO₃crystal. Stuies on theOH-absorption Lorentz three decomposition and the decay curves of upconversiongreen emission show that Zn²⁺ions would push Er³⁺ions from Li sites into Nb sites,and the Er³⁺cluster sites are formed at lower concentration.The defect structure and optical characteristics of Yb/Er:LiNbO₃crystal dopedwith1,2and3mol%In³⁺ions are studied. The experiemtal results show that Yb3+and Er³⁺ions decrease the threshold concentration of In³⁺ions. When theconcentration of In³⁺ion is equal to its threshold, the Er³⁺cluster sites are formed.The formation of Er³⁺cluster sites is favor for the1.54μm near infrared emissiondue to the sensization effect of Yb3+ion. The strongest intensity of1.54μmemission is observed in Yb/Er:LiNbO₃crystal codoped with the thresholdconcentration of In³⁺ions.Zr⁴⁺ion doping enhances the1.54μm emission in Zr/Er:LiNbO₃andZr/Yb/Er:LiNbO₃crystals. Raman spectra and the decay curves of Er³⁺4I11/2�'4I15/2transition at1020nm indicate that the enhancement of the1.54μm emission arisesfrom the increased maximum phonon energy of host material. The near infraredspectra of Yb/Er:LiNbO₃crystals doped with the different valence Zn²⁺, In³⁺andZr⁴⁺ions suggest that Zn²⁺doping decreases the1.54μm emission, In³⁺ions havealmost no effect, and Zr⁴⁺ions lead to a drastical increase of1.54μm emission.Zr/Yb/Er:LiNbO₃crystal could be considered as the most outstanding host materialsfor waveguides.The spectral characteristics of Er:LiNbO₃and Yb/Er:LiNbO₃crystals dopedwith Zn²⁺, In³⁺and Zr⁴⁺ions are studied by Judd-Ofelt theory, and Zr/Yb/Er:LiNbO₃crystal has the largest spectroscopic quality factor. The emission performance of1.54μm emission is analyzed by McCumber and Füchtbauer-Ladenburg theory. Allthe crystals have large emission cross section, which is suitable for the hostmaterials of EDWA.