Growth of near‐stoichiometric LiNbO3 crystals and Li2O contents determination

Two kinds of near‐stoichiometric LiNbO₃ crystals (SLN11 and SLN19) were grown by a flux pulling method from stoichiometric melt with addition of 11mol%K₂O and 19mol%K₂O, respectively. Compared with the congruent melting LiNbO₃, the ultraviolet absorption edges of two crystals shift towards shorter wavelengths, and the locations of the OH^‐ infrared absorption band have obvious change and the bandwidths become greatly narrower. From these experimental results, the Li₂O contents are determined indirectly to be about 49.6mol% for SLN11 and 49.9mol% for SLN19, respectively. The Li₂O content in SLN19 is very close to the ideal value of 50mol%. The coercive fields of two crystals were measured by the poling method at room temperature. A linear relationship between the Li₂O content and the coercive field was fitted. (© 2004 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)     

Growth and photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals grown by Czochralski method

In this paper, photorefractive properties of Mg:Ce:Cu:LiNbO₃ crystals were studied. The crystals doped with different concentration of Mg ions have been grown by the Czochralski method. Mg concentrations in grown crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP‐OE/MS). The crystal structures were analyzed by the X‐ray powder diffraction (XRD), ultraviolet‐visible (UV‐Vis) absorption spectra and infrared (IR) transmitatance spectra. The photorefractive properties of crystals were experimentally studied by using two‐beam coupling. In this experiment we determined the writing time, maximum diffraction efficiency and the erasure time of crystals samples with He‐Ne laser. The results showed that the dynamic range (M/#), sensitivity (S) and diffraction efficiency (η) were dependent on the Mg doping concentration, and the Mg(4.58mol%):Ce:Cu:LiNbO₃ crystal was the most proper holographic recording media material among the six crystals studied in the paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved blue photorefractive properties of near‐stoichiometric LiNbO3:Mn:Fe:Zr crystal

Near‐stoichiometric LiNbO₃ single crystal tri‐doped with ZrO₂, MnO and Fe₂O₃ was grown from Li‐riched melt by Czochralski method. The defect structures and composition of these crystals were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of 3466 cm^‐1 peak in infrared spectra showed that the crystal grown from Li‐riched melt was near stoichiometric. The photorefractive properties at the wavelength of 488 nm and 633 nm were investigated with two‐beam coupling experiment, respectively. The experimental results showed that the response speed and sensitivity were enhanced significantly and the high diffraction efficiency was obtained at 488 nm wavelength. This manifested that near‐stoichiometric LiNbO₃:Mn:Fe:Zr crystal was an excellent candidate for holographic storage. (© 2010 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)     

Effect of reduction/oxidation treatment on blue photorefraction in In:Fe:Cu:LiNbO3 crystals

In:Fe:Cu:LiNbO₃ crystals with reduced/oxidized treatments were prepared by the Czochralski method. The defect structure was analyzed by the UV‐Visible absorption spectra. The blue photorefractive properties, such as the refractive index change, response time, recording sensitivity, dynamic range as well as two‐wave coupling gain coefficient, were also investigated at 488 nm wavelength using the two‐wave coupling experiment. Comparing the as‐grown and oxidized In:Fe:Cu:LiNbO₃ crystals, the reduced sample has the highest recording sensitivity and largest dynamic range. Meanwhile, the high diffraction efficiency is still maintained. Experimental results definitely show that reduction treatment is an effective method to improve the blue photorefractive performance of In:Fe:Cu:LiNbO₃ crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The growth and photorefractive effect of co‐doped Ce:Cu:BSO crystals

In the paper Ce:Cu:BSO crystal has been grown by Czochralski method for the first time with doping CeO₂ and CuO into BSO(Bi₁₂SiO₂₀) crystal. The exponential gain coefficient and respond time of Ce:Cu:BSO crystal are measured by two‐wave‐coupling technology. The results indicate that exponential gain coefficient of Ce:Cu:BSO is more than two times as that of non‐doped BSO and the response time exhibits in microsecond level. Furthermore its exponential gain coefficient improves greatly compared with Ce:BSO's at the same doping level of Ce, while its response time is less than Ce:BSO's. The improvement mechanism of photorefractive effect of Ce:Cu:BSO crystal is investigated systematically. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near‐stoichiometric LiNbO3:ZrO2 single crystal growth by micro pulling down method

Crack‐free, rod‐shaped single crystals of undoped and 0.5, 0.7 and 1.0 mol% ZrO₂‐doped LiNbO₃ with a near‐stoichiometric composition were grown by the micro‐pulling down (μ‐PD) method. The structural properties of the grown crystals were examined by powder X‐ray diffraction (XRD). Electron probe micro analysis (EPMA) of the near‐stoichiometric LiNbO₃ single crystals revealed the homogeneous incorporation of Zr ions. The change in the refractive index and IR transmission spectra of the grown crystals were examined as a function of the Zr concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Czochralski growth of Lu1‐xScxBO3:Ce solid solution crystals

Single crystals of Lu_1‐xSc_xBO₃:Ce (x=0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. Continuous solid solution with calcite structure and a linear compositional dependency of crystal lattice parameter in the system Lu_1‐xSc_xBO₃:Ce are formed and their symmetry belong to hexagonal system with R3c space group checked by X‐ray powder diffraction. The electron probe micro‐analysis measurements show that the main inclusions in Lu_1‐xSc_xBO₃:Ce crystals are in the form of Sc rich oxide and Ce rich oxide. The ICP‐AES tests show that the more Sc ion content in Lu_1‐xSc_xBO₃:Ce, the smaller effective segregation coefficient of Ce in crystal will be. The X‐ray excited luminescence spectra of Lu_1‐xSc_xBO₃:Ce crystals all present a double peaked emission band with maxima round 370 and 400 nm corresponding to Ce³⁺ emission and a self trapped excitons (STE) band peaking at 269 nm. In addition, due to high density, high relative light yield, fast decay time and no‐hygroscopic property, Lu_0.8Sc_0.2BO₃:1 at%Ce crystal could be a good candidate material for scintillation application by improving the crystal quality and cerium concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zn,Co双掺杂近化学计量比LiNbO_3晶体的生长及性能

以K_2O为助熔剂,应用坩埚下降法生长出了Co~(2+) 初始浓度为0.5 mol;,以及ZnO分别为3 mol;与6 mol;的单掺与双掺杂SLN晶体(分别用SLN0, SLN3, SLN6表示).测定了晶体上下部位的吸收与发射光谱.在晶体的吸收光谱中均可观察到520 nm,549 nm,612 nm,1447 nm四个吸收峰,表明Co~(2+)处于晶体的八面体场中.ZnO的掺入明显地改变了吸收峰的相对强度.在520 nm光的激发下,观察到776 nm的荧光发射,其荧光强度的相对强弱也与ZnO的掺杂量有明显的联系.从吸收边带估算出SLN0, SLN3, SLN6晶体中Li2O的含量分别为49.06 mol;,49.28 mol;, 49.10 mol;.ZnO的掺杂量对Co~(2+)在铌酸锂晶体中的浓度分布有很大的影响作用,当ZnO的掺入量为3 mol;时,明显地抑制了Co~(2+)在LiNbO_3晶体中的掺入,当ZnO掺杂量达到6 mol;时,抑制作用减弱.本文从Zn~(2+)在LiNbO_3中随浓度变化的分凝情况以及对Co~(2+)的排斥作用解释了Co~(2+)在晶体中的分布特性以及光谱的变化情况.     

Investigation on the blue photorefractive properties varied with MgO codoping in Ru:Fe:LiNbO3 crystals

Mg:Ru:Fe:LiNbO₃ crystals with various doping concentration of MgO have been grown by Czochralski method. The type of charge carriers and photorefractive properties in Mg:Ru:Fe:LiNbO₃ crystals were measured by two‐wave coupling method using Kr⁺ laser (476 nm) and He‐Ne laser (633 nm) as light sources. We found that holes were the dominant charge carriers under blue light irradiation while electrons were the dominant charge carriers under red light irradiation. Mg²⁺ ions behaved no longer as damage resistant, but promoter to the photorefractive properties at 476 nm wavelength. The photorefractive properties under blue light improved with the increase concentration of Mg²⁺ ions. The enhancement mechanisms of the blue photorefractive were suggested. Experimental results definitely showed that Mg‐doped two‐centre Ru:Fe:LiNbO₃ was a promising blue photorefraction material for holographic volume storage.     

Optical damage resistance of Mg:Ce:Fe:LiNbO3 crystals

Mg:Ce:Fe:LiNbO₃ crystals were prepared with fixed concentrations of Fe₂O₃ and CeO₂, and differing concentrations of MgO by the Czochralski technique. Their infrared transmission spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the photoinduced birefringence change and transmission facula distortion method. The optical damage resistance of Mg:Ce:Fe:LiNbO₃ crystals increases remarkably when the concentration of MgO exceeds a threshold concentration. The dependence of the optical damage resistance on the defect structure of Mg:Ce:Fe:LiNbO₃ crystals is discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of oxygen vacancies in the coloration of 0.65Pb(Mg1/3Nb2/3)O3‐0.35PbTiO3 single crystals

The coloration and oxygen vacancies in 0.65Pb(Mg_1/3Nb_2/3)O₃‐0.35PbTiO₃ (PMN‐PT(65/35)) (starting composition) single crystals grown by a so‐called modified Bridgman technique were investigated in this paper. Light yellow and dark brown colored crystals were generally observed for the typical as‐grown PMN‐PT(65/35) single crystals. X‐ray diffraction results demonstrated that they were both of pure perovskite structure, but good electric properties were only obtained for the light yellow crystal. X‐ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of its components. The O 1s photoelectron spectra of the dark brown colored crystals located at the higher binding energy side, which meant the existence of the more oxygen vacancies. It accordingly led to the formation of the low valence cations associated with the coloration of the crystals, which is also testified by the obtained X‐ray photoelectron spectra of Ti and Nb. (© 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)     

Crystal growth,optical and luminescence properties of (Ce,Sr)‐doped PrAlO3 single crystals

Using the micro‐pulling‐down method, (Ce,Sr)‐doped PrAlO₃ square‐shaped single crystals (4×4×12 mm) were grown. Structural parameters studied by X‐ray powder diffraction were consistent with R3m space group. Compositional homogeneity was checked with electron probe micro‐analysis and found quite uniform. Absorption spectra and luminescence characteristics under UV and X‐ray excitations were measured at room temperature with no Ce‐related emission appeared. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical and dielectric studies on K1‐x(NH4)xH2PO4 mixed crystals grown from z‐cut seeds

Mixed crystals of K_1‐x(NH₄)_xH₂PO₄(KADP) were grown from KDP (KH₂PO₄) dominated mixed solutions with varying molar proportion of ADP (NH₄H₂PO₄) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z‐axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase‐shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10²∼10⁴Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo‐resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band. (© 2010 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)     

The growth and spectral analysis of mixed crystal of Yb‐doped Lu0.5Y0.5PO4 mixed crystals

A new kind of 5 at% Yb‐doped Lu_0.5Y_0.5PO₄ crystals were firstly grown by spontaneously nucleated high‐temperature solution method using lead pyrophosphate (Pb₂P₂O₇) as the solvent. The X‐ray powder diffraction (XRPD) patterns recorded at room temperature showed the crystals possessed tetragonal xenotime structure. The polarized absorption spectra and the fluorescence spectra of Yb:Lu_xY_1‐xPO₄ were measured at room temperature, respectively. The results show that Yb:Lu_xY_1‐xPO₄ mixed crystal will be a promising laser material if the crystal size and quality is further improved.     

Effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate

The effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate was studied. The absorption spectra examination of Ru‐doped LiNbO₃ crystals with different post treatments showed that the absorption coefficient at 530 nm increased after the reduced treatment was employed and the absorption edge of the reduced crystal shifted towards the infrared band. On the contrary, the trend reversed after the oxidized treatment was employed. In addition, the photorefractive properties were investigated with the two‐beam coupling method conducted via a 532 nm solid state laser. It was found that the oxidized Ru:LiNbO₃ had smaller exponential gain coefficient and diffraction efficiency because the charges in the shallow level were exchanged to the deep level. On the other hand, the reduced Ru:LiNbO₃ crystals had larger exponential gain coefficient and diffraction efficiency due to the increase of the Ru³⁺ which existed in the shallow level. The response times of both oxidized and reduced Ru:LiNbO₃ were longer than those of the as‐grown ones. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)