To determine the defect structure of ZnO-doped LiNbO3 single crystals with high doping concentrations, we obtain the measurements using the extended x-ray absorption fine structure (EXAFS) at room temperature. It indicates Zn atom is directly substituted on the Li site of the LiNbO3 crystal after Zn doping. EXAFS simulation by way of analyzing the scattering amplitudes also shows that the Zn atom does not substitute the Nb site at highly Zn-doped LiNbO3. Finally, we confirm that VNb5−, a strong charged vacancy, should be considered as an important factors in influencing the physical properties of LiNbO3 beyond 7.5mol% Zn-doped doping concentration.

A 1 (TO) phonons and OH À absorption spectra of Zn-doped lithium niobate crystals were measured by Raman and infrared spectroscopies at room temperature. Zn doping concentrations are from 0 to 8.1 mol.%. The characterizations of A 1 (TO)-phonon lineshapes and OH À absorption bands as a function of Zn concentration were carried out. The results revealed from Raman and OH À absorption analyses show consistency in the changes of phonon lineshapes and OH À absorption bands. The spectra revealed three different stages of Zn substitution. Based on the Li-vacancy model, the proposed Zn substitution mechanism is: (i) below 5.3 mol.%, Zn atoms replace Li atoms and the total number of Li vacancies is reduced; (ii) from 5.3 to 7.5 mol.% doping, Zn atoms still replace Li atoms but the number of vacancies increases; (iii) above 7.5 mol.% doping, Zn atoms start to replace Nb atoms.

Results of femtosecond pump-probe measurement of E(TO)-like polaritons in Zn-doped lithium niobate crystals are presented. The impulsive-stimulated-Raman-induced three delay-time oscillations, ω1, ω2 and ω3, are found and assigned to the linear combinations of three lowest E(TO)-like polaritons, ν1, ν2, and ν3, which are ω1=ν2-ν1, ω2=ν3-ν1 and ω3=2ν1. The obtained frequencies of ω1, ω2 and ω3 are well explained by dielectric dispersion calculation. The lifetimes of these oscillations induced by the electro optical effect are also deduced, and they are strongly correlated with the Raman lineshape of E(TO) phonons. Our results also imply that the vibrations of E(TO1) and E(TO2) are mainly attributed to the Nb and O atomic motions, while the vibration of E(TO3) is dominated by the defect structure.