Li Dai

OH− absorption and holographic storage properties of Sc(0, 1, 2, 3):Ru:Fe:LiNbO3 crystals

A series of Sc:Ru:Fe:LiNbO3 crystals with various levels of Sc2O3(0, 1, 2, and 3 mol%) doping were grown from congruent melts in air by using the Czochralski technique. The defect structures and photorefractive properties of the Sc:Ru:Fe:LiNbO3 crystals were investigated by acquiring infrared spectra of the crystals and performing two-wavelength nonvolatile experiments, respectively. Our results showed the holographic storage properties of Ru:Fe:LiNbO3 crystals to be enhanced by doping them with a high concentration of Sc2O3, and indicated Sc:Ru:Fe:LiNbO3 crystals to constitute a promising medium for holographic storage.

EFFECT OF HfO2-CODOPING CONCENTRATION ON THE OPTICAL PROPERTIES OF Er3+-DOPED LiNbO3

A series of Hf, Er co-doped LiNbO3 crystals were grown by Czochralski technique with 1 mol% of Er2O3 and with 2, 4, 6 and 8 mol% of HfO2, respectively. The optical damage resistance of Hf:Er:LiNbO3 crystals was studied by the transmitted beam pattern distortion method. The optical damage resistance of Hf (6 mol%): Er:LiNbO3 crystals is about two orders of magnitude higher than that in Hf:Er:LiNbO3. The X-ray power diffraction, the ultraviolet-visible absorption spectra and the infrared absorption spectrum were measured and discussed in terms of the spectrometric characterization and the defect structure of crystals. The results showed that with mild co-doping with HfO2, Er3+ substitutes Nb5+, whereas with heavy co-doping, a part of Er3+ substitutes Li+. The structure defects were discussed in this paper to explain the improvement of the optical damage resistance in the Hf:Er:LiNbO3.

EFFECT OF Li/Nb RATIO ON GROWTH AND SPECTROMETRIC CHARACTERIZATION OF Hf:Fe:LiNbO3 CRYSTALS

Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.946, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by XRD, UV-Vis and IR spectroscopy. The results show that the threshold concentration of Hf in LiNbO3 crystals decrease with the increasing of the Li/Nb ratio; when the Li/Nb ratio is 1.05, the threshold concentration of Hf is less than 2 mol%, largely under the threshold concentration of Hf ions in congruent Hf:Fe:LiNbO3 crystal (4 mol).1–3 With the increase of Li/Nb, Hf ions first replace the ; when the concentration of Hf ions is higher than the threshold value, Hf ions occurs on normal Nb and Li sites.

Influence of magnesium concentration on the optical properties of ytterbium and holmium co-doped lithium niobate crystal

In this paper, a series of Yb (0.5mol.%):Ho (0.5mol.%):LiNbO3 crystals doped with various concentration of Mg2+ (1, 3, 5 and 7mol.%) were grown by the Czochralski technique. The ability of optical damage resistance of Mg:Yb:Ho:LiNbO3 crystals increases with increasing the Mg2+ doping concentration. The optical homogeneity of Mg:Yb:Ho:LiNbO3 crystals doped with different concentration of Mg2+ was detected using the birefringence gradient method. The results demonstrated that the optical homogeneity is getting better with the increase of the Mg2+ doping concentration. The studies on the infrared transmission spectra indicated that Mg2+ ions first replaces anti-site NbLi4+ in the form of MgLi+ defect, once the concentration of Mg2+ reaches or exceeds the threshold concentration, it begins to substitute Li-site and Nb-site of normal lattice and form defect of MgNb3−−3MgLi+. Therefore, the change of Mg2+ doping concentration is the fundamental reason leading to a violet shift of the OH− absorption peak.

Dopant occupancy and UV-VIS-NIR spectroscopy of Mg (0, 4, 5 and 6 mol.%):Dy:LiNbO3 crystal

A series of Dy:LiNbO3 crystals with x mol.% Mg2+ ions (x =0, 4, 5 and 6 mol.%) were grown by the Czochralski method. The effective segregation coefficient of Mg2+ and Dy3+ ions was studied by the inductively coupled plasma-atomic emission spectrometry (ICP-AES). UV-VIS-NIR absorption spectra and Judd–Ofelt theory were used to investigate their spectroscopic properties. J–O intensity parameters (Ω2 = 7.53 × 10−20cm2, Ω4 = 6.98 × 10−20cm2, and Ω6 = 3.09 × 10−20cm2) and larger spectroscopic quality factor (X = 2.26) for Mg:(6 mol.%)Dy:LiNbO3 crystals were obtained.

Investigations on growth and property of mid-infrared lithium selenoindate single crystals

Lithium selenoindate (LiInSe2) crystals with high optical quality are successfully grown by small-angle inclined horizontal temperature gradient condensation. In order to evaluate the various characteristics, the powder X-ray diffraction (XRD) spectrum, optical damage resistance ability and Vickers hardness in lithium selenoindate crystals were studied. The growth crystals have orthorhombic nature, a = 6.184xa0A, b = 7.092xa0A and c = 8.207xa0A. The damage thresholds of LiInSe2 crystal with the front face and back face were 224xa0mW/cm2 and 165xa0mW/cm2. Also the Vickers hardness number of LiInSe2 crystal was found to be 342.4xa0kg/mm2.

Enhancement of blue photorefractive properties in Mg:Fe:Cu:SLiNbO3 crystals with near stoichiometry

Using the top seeded solution growth technique, near stoichiometric Mg:Fe:Cu:SLiNbO3 crystals have been grown by using K2O as flux. Infrared transmission spectra were measured and defect structure and change of threshold value were investigated. Using Kr+ laser as light source (blue light with wavelength of 476 nm) the photorefractive properties of crystals were measured. The diffraction efficiency of 76.3%, the short response time of 11 s, the dynamic range of 27.39, the sensitivity of 2.09 cm/J, and the refractive index change of 8.67 × 10-5 were obtained. The blue photorefractive properties were enhanced. As the holes are the dominant charge carriers, the short wavelength blue light which exhibits high energy can excite the holes from both of the shallow and the deep trap centers with the same phase. It was found that the so-called optical damage-resistant dopant such as Mg2+ ions no longer functioned as the damage resistant at 476 nm wavelength, but turned to enhance the blue photorefractive characteristics.

IMPROVEMENT OF NONVOLATILE BLUE PHOTOREFRACTIVE PROPERTIES IN In:Ce:Cu:LiNbO3 CRYSTALS

The In:Ce:Cu:LiNbO3 crystals used in this work were grown by Czchralski method. The key parameters: the exponential gain coefficient Γ, the diffraction efficiency ηS, the response time τw, the dynamic range M/#, the sensitivity S and the maximal refractive index change Δnmax were measured with conventional two beam coupling. The optimal values of Γ, ηS, M/#, S and Δnmax achieved are 44.7, 68.6%, 6.02, 0.471 cm/J and 5.37 × 10-5, respectively. It was found that the blue light photorefractive properties of Γ, ηS, M/#, S and Δnmax increased with increasing In3+ ions concentration, while the red light photorefractive properties of Γ, ηS, Δnmax decreased with increasing In3+ ions concentration. The nonvolatile holographic storage properties were measured by both the dual wavelength and two color techniques. The maximal diffraction efficiency and fixing diffraction efficiency using the dual wavelength technique were doubled compared to those obtained in using the two color technique. The sensitivity and nonvolatile sensitivity were one order of magnitude higher than those by the two color technique. The photorefractive property enhancement by the dual wavelength technique was investigated.

INVESTIGATIONS ON DEFECT STRUCTURE AND LIGHT-INDUCED SCATTERING OF Mg:Ho:LiNbO3 WITH VARIOUS Mg2+ CONCENTRATION

Congruent Ho3+ (1 mol.%): LiNbO3 crystals codoped with MgO (X mol.%, X = 1, 3, 5 and 7) were grown by the Czochralski technique. The ultraviolet-visible (UV-Vis) and infrared (IR) spectra were measured in order to analyze the defect structure of the crystals. The concentrations of Mg, Ho, Li and Nb in the crystals were carried out with an inductively coupled plasma atomic emission spectrometer. Experimental results indicates as Mg2+ doping concentration increases in melt, the distribution coefficients of Mg and Ho ions decrease, the Li/Nb ratio in the crystals decreases first and then increases, and the absorption edge shifts to a shorter wavelength. The light-induced scattering of Mg:Ho:LiNbO3 crystals was quantitatively scaled via the incident exposure energy. The results demonstrated that Mg (7 mol.%): Ho:LiNbO3 crystal had the weakest light-induced scattering and the mechanism related to their defect structures was discussed.

JUDD–OFELT THEORY ANALYSIS AND SPECTROSCOPIC PROPERTIES OF Ho:LiNbO3

A series of Ho:LiNbO3 crystals with various concentration of Ho2O3 were grown by Czochralski technique. Transmittance spectrum, absorption spectrum and modified Judd–Ofelt approach have been used to investigate its spectroscopic properties. Ho concentrations in crystals were analyzed by an inductively-coupled plasma optical emission spectrometry (ICP-OE/MS). The results of the spectroscopic analysis of transition strengths for Ho ion in a series of Ho:LiNbO3 crystals with various Ho content are reported. It is concluded that all the Ωλ values of the Ho ion decrease with increasing Ho content. For Ho (4 mol%): LiNbO3, the obtained intensity parameters and radiative lifetime of the 5I5 level are: Ω2=5.75×10-20 cm2, Ω4=22.69×10-20 cm2, Ω6=14.10×10-20 cm2, and τ=4.08 ms respectively. The results showed that the Ho2O3-codoped LiNbO3 crystal increases the Ho ion radiative lifetimes, but has less influence on the fluorescence branching ratio.