In doping effect on optical properties in Zn:In:Fe:LiNbO3 crystals

A series of Zn:In:Fe:LiNbO₃ crystals were prepared by Czochralski method. The crystal composition and defect structure were analyzed by ICP‐OE/MS, UV–vis and IR spectroscopy. The results show that with increasing In³⁺ doping concentration in melt, the segregation coefficients of both Zn and In ions decrease. The optical damage resistance of Zn:In:Fe:LiNbO₃ crystals was studied by the transmitted beam pattern distortion method. It is found that the optical damage resistance of Zn:In(3mol%):Fe LiNbO₃ crystals is two orders of magnitude higher than that of Zn:Fe:LiNbO₃. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and Photo‐Damage Resistance of Li‐Rich LiNbO3 Crystals Co‐Doped with Zn2+/Er3+

The pure congruent LiNbO₃, Er:LiNbO₃ and Zn,Er co‐doped Li‐rich LiNbO₃ crystals were grown by Czochralski method. The X‐ray diffraction method and ultraviolet‐visible absorption spectra of the crystals were used to analyze the structure of the crystals. The photo‐damage ability resistance of the crystals was measured. The Zn,Er co‐doped Li‐rich LiNbO₃ crystals show a decrease in lattice constant values, a shift in absorption edge of ultraviolet‐visible absorption spectra towards shorter wavelength, and three orders of magnitude increase in photo‐damage resistance compared to congruent LiNbO₃ crystal. The intrinsic and extrinsic defects are discussed to explain the enhance of the photo‐damage ability resistance     

Increased optical damage resistance of Zr:LiNbO3 crystals

Zr: LiNbO₃ crystals has been grown. The crystal composition and phase are analyzed by X‐ray diffration. The optical damage resistance ability of Zr: LiNbO₃ crystals is studied by the Sénarmont compensation method and the transmitted beam pattern distortion method. The saturated value of the birefringence change of 6 mol% Zr: LiNbO₃ crystal is 1.01×10^‐4, which is seven times smaller than that of congruent pure LiNbO₃ crystal. The results of UV‐Visible and IR absorption spectra of Zr: LiNbO₃ crystals powerfully confirm that the optical damage resistance threshold concentration of the Zr⁴⁺ ions doped in LiNbO₃ crystals is about 6 mol% in the melt. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and light‐induced scattering of Zr‐doped near‐stoichiometric Mn:Fe:LiNbO3 crystals grown by TSSG method

Near‐stoichiometric Mn:Fe:LiNbO₃ crystals doped with various concentration of ZrO₂ were grown by top seed solution growth (TSSG) method in the air atmosphere. The Zr concentration in the crystal was determined by inductively coupled plasma optical emission spectrometer. The defect structures were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of vibration peak at 3466 cm^‐1 in infrared spectra manifested that Li/Nb ratio in crystals approached to stoichiometric proportion. The fundamental absorption edge represented continuous red‐shift which was discrepancy with congruent doped LiNbO₃ crystals showed that doping ions possessed different location mechanism. The light‐induced scattering of the doped stoichiometric LiNbO₃crystals were quantitatively scaled via incident exposure energy. The results demonstrated that Zr(2 mol%):Mn:Fe:LiNbO₃ crystal had the weakest light‐induced scattering and the mechanism related to their defect structures was discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Second Harmonic Generation in Zn‐doped Li‐rich LiNbO3 Crystals

6.0 mol. % ZnO doped LiNbO₃ crystals were grown by Czochralski technique. Various Li/Nb mole ratios of 0.942, 0.970, 1.000, and 1.020 were used to prepare the starting materials. Second harmonic generation (SHG) experimental results show that the phase matching temperature increases near linearly with the increasing of Li/Nb ratio, and the SHG efficiency is enhanced by the Zn doping and the increasing of Li/Nb ratio. The intrinsic and extrinsic defects are discussed in this paper to explain the SHG behavior and photo‐damage resistance in the Zn doped Li‐rich LiNbO₃ crystals.     

Influence of Mg/Er co‐doping on the principal laser parameters of LiNbO3 crystals

Mg: Er: LiNbO₃ crystals were grown by the Czochralski technique with various concentrations of MgO = 2 mol%, 4 mol%, 6 mol% and the fixed concentration of Er₂O₃= 1 mol% in the melt, and the 8 mol%Mg: 1 mol%Er: LiNbO₃ crystal was fabricated by the Czochralski technique with special technology process. The crystals were treated by polarization, reduction and oxidation. The segregation coefficients of Mg²⁺ and Er³⁺ in Mg: Er: LiNbO₃ crystals were measured by X‐ray fluorescence spectrograph, as well as the crystal's defect structure and optical properties were analyzed by the UV‐Vis, IR and fluorescent spectroscopy. The pump wavelength and the surge wavelength were determined. Using m‐line method tested optical damage resistance of those crystals, the results show that photodamage threshold of Mg: Er: LiNbO₃ crystals are higher than that of Er: LiNbO₃ crystal, and the oxidation treat could enhance the photodamage resistant ability of crystals while the reduction treat could depress the ability. The optical damage resistance of 8 mol%Mg: 1 mol%Er: LiNbO₃ crystal was the strongest among the samples, which was two orders magnitude higher than that of 1 mol%Er: LiNbO₃ crystal. The dependence of the optical properties on defect structure of Mg: Er: LiNbO₃ crystals was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of doping on OH absorption in LiNbO3 crystals

Undoped, Cr doped and Mg, Cr codoped LiNbO₃ crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV‐Visible spectroscopy. Infrared optical absorption for OH^– ion has been used to study the effect of dopants on the crystals. The peak position of OH^– shift to 3535 cm^‐1 for Mg, Cr codoped crystals compared to 3484 cm^‐1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm^‐1) and 653 nm (15313 cm^‐1) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm^‐1) and 678 nm (14749 cm^‐1). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO₃ crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and optical damage resistance of Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Hf:Fe:LiNbO₃ crystals were grown in air by the Czochralski technique with various ratios of [Li]/[Nb]=0.94, 1.05, 1.20 in melt. The defect structure and location of doped ions were analyzed by the UV‐visible and infrared spectroscopy. The optical damage resistance ability of Hf:Fe:LiNbO₃ crystals was measured by the photo‐induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals is enhanced with the increase of the [Li]/[Nb] ratio. The dependence of the optical damage resistance of Hf:Fe:LiNbO₃ crystals on the defect structure is discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure defects and optical damage resistance in doubly doped In:Nd:LiNbO3 crystal waveguide substrates

A series of In:Nd:LiNbO₃ crystals were grown by Czochralski technique and were made into waveguide substrates. The optical damage resistance of the In:Nd:LiNbO₃ waveguide substrates was characterized by measurement of the holographic method. The optical damage resistance of In (3.0 mol%):Nd:LiNbO₃ was much higher than that of other In:Nd:LiNbO₃. The ultraviolet‐visible (UV‐Vis) absorption spectra the In:Nd:LiNbO₃ crystals were measured and investigated. The structure defects were discussed in this paper to explain the enhance of the optical damage resistance in the In:Nd:LiNbO₃ crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical absorption spectra of LiNbO3, Fe:LiNbO3, and Zn:Fe:LiNbO3 single crystals grown by Bridgman method

The optical absorption spectra of LiNbO₃ (LN), Fe:LiNbO₃ (Fe:LN), and Zn:Fe:LiNbO₃ (Zn:Fe:LN) single crystals grown by Bridgman method were measured and compared. The absorption characteristics of the samples and the effects of growth process conditions on the absorption spectra were investigated. The Fe, Zn and Li concentrations in the crystals were analyzed by inductively coupled plasma (ICP) spectrometry. The results indicated that the overall Fe ion and Fe²⁺ concentration in Fe:LN and Zn:Fe:LN crystals increased along the growing direction. The incorporation of ZnO in Fe:LN crystal induced increase of Fe²⁺ in the crystal. Among Fe‐doped and Zn:Fe‐codoped LN single crystals, 3 mol% ZnO doped Fe:LN had a biggest change of Fe²⁺ ion concentration from bottom to top part of crystal. The effects of technical conditions (atmosphere and thermal history) on Fe²⁺ ion concentration were discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and spectroscopic characteristics of codoped Hf: Er: LiNbO3 crystals

Codoped Hf: Er: LiNbO₃ crystals have been grown by the Czochralski technique. Defect structures of the crystals were analyzed by IR absorption spectra, and the compositions of the crystals were measured by X‐ray fluorescent spectrograph. A new OH^–‐associated vibrational peak at 3492 cm^–1 was revealed in 6 mol % Hf: 1 mol % Er: LiNbO₃ crystal. It was attributed to (Hf_Nb)^–‐OH^–‐(Er_Nb)^2– defect centers. The Er³⁺ concentrations in crystals gradually decreased with the increase of the codoped Hf⁴⁺ concentrations in the melts. The emission characteristics of the crystals were investigated by the fluorescence spectrum. It was found that the luminescent intensity in codoped 6 mol % Hf: 1 mol % Er: LiNbO₃ crystal was 3.5 times stronger than that in single doped 1 mol % Er: LiNbO₃ crystal. The luminescent enhancement effect was successfully explained on the basis of defect structure of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and optical homogeneity investigations of Fe and Fe:Mn codoped LiNbO3 crystals

Lithium niobate (LiNbO₃) crystals doped with Fe and Fe:Mn were grown by Czochralski technique. The doping concentrations of Fe and Mn were optimized. Transmission studies reveal broad absorption band centered at 488 nm. The UV cutoff observed for Fe doped LiNbO₃ is 358 nm whereas for Fe:Mn codoped LiNbO₃ is 352 nm. This decrease in UV cutoff for Fe and Mn codoped LiNbO₃ compared to only Fe doped LiNbO₃ is due to the increase in Li/Nb ratio. Optical homogeneity was assessed using conoscopy and birefringence interferometry. Dark and photo conductivity measurements prove that LiNbO₃ is a negative photo conducting material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure characteristics in near‐stoichiometric In:LiNbO3 single crystals grown by K2O‐flux method

With K₂O as flux, near‐stoichiometric In:LiNbO₃ (In:SLN) crystals with different indium contents were grown by the top seed solution growth (TSSG) method. Defect structure characteristics and the replacement principle of extrinsic ions were derived from X‐ray powder diffraction, differential thermal analysis (DTA), ultraviolet‐visible (UV) absorption and infrared (IR) spectrum measurement. Further analysis indicated that the threshold concentration of In₂O₃ in near‐stoichiometric LiNbO₃ crystals were about 1.1 mol%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure and optical properties of Zn:Mn:Fe:LiNbO3 crystals

Zn:Mn:Fe:LiNbO₃ crystals were prepared by Czochralski technique. Its microstructure was measured and analyzed by UV‐Vis absorption spectra. The optical damage resistance of Zn:Mn:Fe:LiNbO₃ crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of ZnO is over a threshold concentration. Its value in Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is about three orders of magnitude higher that in the Mn:Fe:LiNbO₃ crystal. The dependence of the defects on the optical damage resistance was discussed. The non‐volatile holographic storage was realized in all crystals, and the sensitivity of the Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is much higher than that of others. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of microscopic defects on optical damage resistance of Zn:Fe:LiNbO3 crystals

Influence of defect structure on the infrared transmission spectra of OH^‐ in Zn:Fe:LiNbO₃ crystals with various ZnO concentration and different Li/Nb ratios was investigated. It indicates that above the Zn concentration threshold the OH^‐ absorptions bands successively shift from 3482cm^‐1 to 3504cm^‐1 and 3529cm^‐1. The intensity of the 3504cm^‐1 band increases with ZnO concentration increasing. The optical damage resistance of the Zn:Fe:LiNbO₃ crystals increases rapidly when the ZnO concentration exceeds a threshold value. This result contributed to the site alteration from the Li sites to Nb sites due to Zn‐doping in crystal. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Investigation on photorefractive properties of doped lithium niobate

Cu:LiNbO₃ crystal and Fe:Cu:LiNbO₃ crystals were grown by the Czochralski method from congruent melt. The OH^‐ absorption spectrum of doped lithium niobate crystals was measured. The photorefractive properties of doped crystals were studied by the two‐wave coupling method. The results of the two‐wave coupling experiments showed that as the concentration of doping ions increased, the diffraction efficiency and the dynamic range enhanced, the holographic response time shortened. The recording time of Fe(0.10wt%): Cu(0.10wt%): LiNbO₃ crystal is only a tenth of that of Cu(0.05wt%): LiNbO₃ crystal. Among all samples, the dynamic range of the Fe(0.10wt%): Cu(0.10wt%): LiNbO₃ crystal was the most largest (up to 40.78). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and optical damage resistance of In:Fe:Cu:LiNbO3 crystals with various [Li]/[Nb] ratios

In:Fe:Cu:LiNbO₃ crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios of 0.946, 1.050, 1.200, and 1.380 in melt. Based on the ICP‐AES (inductively coupled plasma atomic emission spectrometry) analyzed results, the chemical formula of the triple‐doped In:Fe:Cu:LiNbO₃ crystals were obtained. It can be seen that the near‐stoichiometric ratio value is between 1.050 and 1.200 for our samples. The optical damage resistance of In:Fe:Cu:LiNbO₃ crystals was characterized by changes in light‐induced birefringence and it increases with the increasing of [Li]/[Nb] ratios. The dependence of the optical damage resistance on the defect structure of In:Fe:Cu:LiNbO₃ crystals is discussed in detail based on the obtained chemical formulas. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterisation of Zn:LiNbO3/Mg:LiNbO3 multilayer thin films grown by liquid phase epitaxy

1, 3 and 5 mol% ZnO doped LiNbO₃ film and 2 mol% MgO doped LiNbO₃ multilayer films were grown on the LiNbO₃ (001) substrate by liquid phase epitaxy (LPE) method with a Li₂O‐V₂O₅ system. We examined the optical transmission spectra of the Zn:LiNbO₃ by Fourier Transform‐Infrared Spectrophotometer (FT‐IR). The crystallinity and the lattice mismatch between the Zn:LiNbO₃ film and Mg:LiNbO₃ film was confirmed by x‐ray rocking curve (XRC) and observed the ZnO and MgO distribution in the cross‐section of the multilayer thin films by electron probe micro analyzer (EPMA). Furthermore, the surface morphology of the films was observed using atomic force microscopy (AFM). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical damage resistance of Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Hf:Fe:LiNbO₃ crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios ([Li]/[Nb]=0.94, 1.05, 1.20) in melt. The defect structure and location of doped ions were analyzed by the UV‐visible absorption spectra. The optical damage resistance of Hf:Fe:LiNbO₃ crystals was investigated by the photoinduced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals decreases with the increase of the [Li]/[Nb] ratio. The dependence of the optical damage resistance of Hf:Fe:LiNbO₃ crystals on the defect structure is discussed in detail. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Micro‐Pulling Down Growth of Co‐doped Lithium Niobate Single Crystal Fibers According Er and Mg Contents and Photolumenescence Properties

The Er³⁺doped Mg:LiNbO₃single crystal fibers employed in our experiment were grown in air by a micro‐pulling down (μ‐PD) method from host materials of a congruent Li/Nb (0.945) ratio which were melt‐doped with a nominal molar concentration of 1, 3, 5% MgO and 0.6% Er₂O₃. The X‐ray diffraction analysis results indicated that the co‐doped crystals main tained the same structural characteristics as the undoped LiNbO₃, however the lattice parameters with Mg differed; c (Å) value decreased, and a (Å) increased than of pure LiNbO₃. The influence of dopants on the photoluminescence (PL) properties of the Er:Mg:LiNbO₃ single crystal fibers excited by laser lines of 514 nm was reported. Also, the PL properties according to temperature and the excitation power of Er:Mg:LiNbO₃ crystal fibers were analyzed.