An initial study of the growth and defect analysis on hydrated 2-benzoyl benzoic acid crystal

In the present study, single crystals of hydrated 2-benzoyl benzoic acid were grown by the slow evaporation solution growth method. Single crystal and powder X-ray diffraction studies confirm the triclinic structure of the grown crystals. The defect in crystalline perfection has been defined by rocking curve analysis. The FTIR spectrum of the crystal displays carbonyl stretching of the carboxylic group at 1685 cm^?1 and of keto group at 1661 cm^?1. It shows a merged medium band around 3450 cm^?1 due to OH stretching and does not distinguish clearly between OH of COOH and H₂O held up in the crystal. The existence of additional bands appears at 1590 cm^?1 due to vibration of H₂O in the compound. The photoluminescence excitation studies were carried out for the grown crystals for wide wavelength range between 300 nm and 700 nm at room temperature. The range of percentage of optical absorption of the crystal has been ascertained by UV?vis spectral characterization. The mechanical strength has been determined by Vickers's microhardness measurement for different loads with constant dwell time.     

Effect of external fields on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe<Subscript>2</Subscript>

The effect of external fields (dc electric field, light illumination) on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe₂ is studied using the measured dielectric constant. The results obtained are discussed. It is shown for the first time that the effect of external fields on the anomaly related to the memory effect in TlGaSe₂ can be reduced to the following universal empirical rule: when a sample is held for many hours at a constant temperature T ₀ in the temperature range of the incommensurate phase in a dc electric field, the deflection amplitude in the low-temperature part of the anomaly in the temperature dependence of the relative change in the dielectric constant Δ?/? increases (the deflection in the high-temperature part of the Δ?/? anomaly disappears) as compared to this segment in the dependence obtained during isothermal annealing of this sample at the same temperature without an electric field. The crystal remembers its thermal history at a temperature that is several kelvins higher than T ₀. Light illumination increases the deflection amplitude in the high-temperature part of the Δ?/?(T) anomaly and shifts the temperature at which the crystal remembers its thermal history toward lower temperatures with respect to T ₀.     

OH-吸收带作为铌酸锂晶体缺陷结构的探针

本文报道了一组不同Li/Nb比和另一组不同掺Mg浓度的LiNbO₃晶体室温OH^-吸收带的实验结果,观察到OH^-吸收带的三峰结构及其随Li/Nb比的变化,以及重掺Mg晶体中(6mol％MgO)OH^-吸收带转变为双峰结构,并向高能端移动54cm^-1。根据LiNbO₃的晶体结构以及Abrahams和Smyth的缺陷结构模型,对化学计量晶体、一致熔化晶体和掺Mg晶体分别进行讨论。并提出重掺Mg晶体中OH^-吸收带向高能端的移动可能是由于当掺Mg浓度超过阈值后Mg²⁺离子开始进入Nb位而引起的。 关键词：     

Edge absorption spectra of crystalline and glassy PbGeS<Subscript>3</Subscript>

Edge absorption spectra of crystalline and glassy lead thiogermanate (PbGeS₃) have been measured in the temperature range from 77 to 470 K. It is shown that the dependence of the absorption coefficient on the photon energy for the glassy and crystalline states in the polarization E ∥ c is described by the Urbach rule. For the crystal in the polarization E ∥ b, at T < 300 K, an almost parallel shift of the intrinsic absorption edge to lower energies occurs with an increase in temperature, whereas at T ≥ 300 K, the Urbach absorption edge is observed. The parameter σ₀, related to the electron-phonon coupling constant, and the energy ?ω_ph of the effective phonons involved in the formation of the absorption edge of crystalline PbGeS₃ are determined from the temperature dependence of the parameter of the absorption edge slope. The contributions of the dynamic and static disorders to the diffusion of the absorption edge of crystalline PbGeS₃, as well as the topological disorder of glassy PbGeS₃, have been estimated.     

Growth, spectroscopic characteristics and laser potential of Yb3+:Ca3La2(BO3)4 crystal

Crystal of Yb³⁺-doped Ca₃La₂(BO₃)₄ has been grown by the Czochralski technique. The room temperature absorption and fluorescence spectra of the crystal have been investigated. The result showed that this crystal exhibits broad absorption and emission with the FWHM of 11 nm at 978 nm and 66 nm FWHM at 1025 nm, respectively. The stimulated emission cross-section of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg method, respectively. The room temperature fluorescence decay curves of ² F _5/2 manifold of Yb³⁺ ions were recorded for both crystal and powder samples. The effect of radiation tapping on the spectroscopic properties is discussed. The result that the lifetime of the powder sample is shorter than that of the bulk sample demonstrates the existence of radiation trapping effect. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.     

Analysis of the absorption coefficient in carbon implanted Nd:YVO<Subscript>4</Subscript> by an annealing process

This work reports the behaviour of the absorption coefficient in a C²⁺-implanted Nd:YVO₄ crystal by successive annealing steps. The absorption coefficient was monitored with respect to time and temperature after an annealing process. Firstly, the annealing duration increased in a constant form keeping a constant temperature and secondly, the annealing temperature was increased with equal time intervals. The results indicate that the variation of the absorption coefficient has an exponential behaviour.     

铁电-顺电扩散相转变的实验和统计模型

制备了扩散相转变铁电陶瓷系列(Ba_1-xLa_x)(Ti_1-yZr_y)O₃和扩散-非扩散相变铁电单晶系列K_0.2Na_0.2(Sr_pBa_1-p)_0.8Nb₂O₆。陶瓷采用一般铁电陶瓷制备工艺,单晶采用提拉法生长。测量了所有样品在-50—100℃范围内 关键词：     

Formation and optical properties of CdSSe semiconductor nanocrystals in the silicate glass matrix

Technological conditions providing the formation of CdS _x Se_1−x semiconductor crystal grains with sizes ranging from 2 to 8 nm in a silicate glass matrix have been determined. As the temperature of forming annealing increases, the size of crystal grains increases without changes in their crystal structure and composition. The observed short-wavelength shift of the optical absorption edge indicates that the quantum confinement affects the energy band structure of the nanocrystals. Intense luminescence of the samples is due to radiative transitions involving defects at the semiconductor nanocrystal-silicate matrix interface or intrinsic defects of nanocrystals.     

纳米掺N TiO2的制备及光谱分析

以钛酸四丁酯(TBT)及乙二胺(EDA)为前驱体,乙醇为溶剂,冰醋酸为抑制剂,通过溶胶-凝胶法制备了纳米掺NTiO2,并对其结构及光谱性质进行了表征,根据差热-热重分析(TG-DTA)确定了所制备样品的晶型转换温度及最佳的煅烧温度;根据紫外-可见漫反射光谱(UV-Vis/DRS)表征了其光谱吸收特性;根据X射线衍射光谱(XRD)确定了其粒径及晶相结构;根据X射线光电子能谱(XPS)分析了其表面组成。实验考察了光谱吸收带红移程度与乙二胺、钛酸四丁酯的配比及煅烧温度的关系。研究结果表明,制备的纳米掺NTiO2为锐钛矿相,其光谱吸收带发生了明显的红移,乙二胺与钛酸四丁酯的配比及煅烧温度对其光谱吸收有明显的影响。当乙二胺与钛酸四丁酯的摩尔比为1:10,煅烧温度为600℃时,所制备样品对可见光的吸收最强。     

Effect of deuteration on the electrical conductivity,dielectric constant and phase transitions in LiNH4SO4

Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high temperature phase transition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNH₄SO₄. Mechanisms of phase transitions and of electrical transport in the crystal are discussed.     

Crystal growth, spectral and laser properties of Yb3+:NaGd(WO4)2 crystal

Yb³⁺-doped NaGd(WO₄)₂ (Yb:NGW) crystal has been successfully grown by Czochralski method. The rocking curves from (400) plane of as-grown Yb:NGW crystal was measured and the full-width values at half-maximum was 21″. The polarized absorption spectra, the fluorescence spectra and the fluorescence decay lifetime of Yb:NGW crystal were measured at room temperature. The spectroscopic parameters of Yb:NGW crystal are calculated and compared, with those of Yb:YAG crystal. A continuous wave output power of 3.01 W at 1048 nm was obtained with a slope efficiency of 71% by use of diode pumping.     

Thermodynamic and magnetic properties of HoRh2Si2: A comparison between experiments and calculations in a crystal field model

The origin of two peaks observed in the magnetization and the heat capacity curves of HoRh₂Si₂ is investigated. The thermodynamic and the magnetic properties of this compound are calculated using a Hamiltonian including crystal field and isotropic exchange interaction terms which are comparable in magnitude. Two components (parallel and perpendicular to the c-axis) of the magnetization are evaluated by the molecular field approximation. The two peaks in the magnetization and the heat capacity can be reproduced by choosing appropriate values for crystal field parameters and molecular field constant. The lower transition temperature corresponds to the temperature at which the perpendicular component of the magnetization disappears, and the higher one, to that at which the parallel component of the magnetization disappears.     

低温高压下的Na5Eu(WO4)4的发光和晶体场参数

用低温金刚石对顶砧高压显微光谱系统在20—300K低温和0—10GPa高压范围内研究了白钨矿型化学计量的基质发光晶体四钨酸铕钠Na₅Eu(WO₄)₄中Eu³⁺的发光.确定了Eu³⁺荧光谱线和能级在低温下的压力移动率.它随温度变化,表明温度和压力对Eu³⁺谱线作用不是独立无关的.按晶体场理论简化方法推导了能级的晶体场参数表达式,并按实验数据拟合出在不同低温下晶体场参数随压力的移     

Nuclear magnetic resonance studies of the structural phase transitions in RbCaF3

Fourier Transform NMR measurements made on a single RbCaF₃ crystal using Rb indicate a structural phase transition at 198 K. The temperature dependence of the quadrupole coupling constant and hence of the order parameter was studied in the range 130 K – 290 K by measuring the second order shift of the central line of Rb resonance. The critical exponent, β, of the order parameter at the transition is found to be equal to 0.33.     

KTiOPO4晶体纵横模劈裂的喇曼谱

在室温下测量了ＫＴｉＯＰＯ₄单晶的偏振喇曼散射谱，应用９０°散射及背散射得到了各模的峰位值，其中Ｂ₁（ＬＯ）模、Ｂ₂（ＬＯ）模的喇曼谱测量尚未见报道过。根据ＬＯ－ＴＯ劈裂的实验结果，计算出该晶体极化模的有效电荷、振子强度及沿对称轴方向的静态介电常数。 关键词：     

Crystal growth, optical properties, and laser operation of Yb3+-doped NYW single crystal

Laser crystal Yb³⁺-doped NaY(WO₄)₂ (Yb:NYW) with excellent quality has been grown by Czochralski technique. The rocking curves from (400) plane of as-grown Yb:NYW crystal was measured and the full-width value at half-maximum was 19.92″. The effective segregation coefficients were measured by the X-ray fluorescence method. The polarized absorption spectra and the fluorescence spectra of Yb:NYW crystal were measured at room temperature. The fluorescence decay lifetime of Yb³⁺ ion in NYW crystal has been investigated. The spectroscopic parameters of Yb:NYW crystal are calculated and compared with those of Yb:YAG crystal. A continuous wave output power of 3.06 W at 1031 nm was obtained with a slope efficiency of 42% by use of diode pumping.     

Optical absorption spectrum of Ni2+ ion doped in synthetic lecontite

The optical absorption spectrum of Ni²⁺ ion doped in lecontite (sodium ammonium sulphate dihydrate) single crystal has been studied at room and liquid air temperatures. All the bands could be assigned assumingO _h symmetry for the Ni²⁺ ion in the crystal. The splitting of³ T _1g (F) band at liquid air temperature has been attributed to spin-orbit interaction. The crystal field and spin-orbit parameters derived areD _q=1000 cm^?1;B=740 cm^?1;C/B=4.27 and ζ=600 cm^?1. All the bands observed show a blue shift when the crystal was cooled to liquid air temperature.     

Spectral studies on erbium doped potassium lithium tantalate niobate single crystal grown by the step-cooling technique

An erbium doped K_0.603Li_0.397Ta_0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550, and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm, 548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of ?⁴ S _3/2→⁴ I _15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO₄)₂ crystal. The crystal might become a promising upconversion laser material. The upconversion mechanism of Er³⁺ in the sample was discussed based on decay curves and pump power dependence analyses in this work.     

Spectroscopic characteristics of Pr<Superscript>3+</Superscript> in biaxial La<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

A Pr³⁺-doped La₂(WO₄)₃ crystal grown by the Czochralski method has been investigated as a promising laser material. The principal axes of the optical indicatrix and Pr³⁺ concentration of the crystal were determined. The polarized absorption, fluorescence spectra and fluorescence decay curves of the main emission multiplets of the crystal were measured at room temperature. The spectroscopic parameters were obtained by the modified Judd–Ofelt theory combined with the normalized method. The peak stimulated emission cross-sections of the major emission lines were estimated. The good spectroscopic properties imply that the Pr³⁺:La₂(WO₄)₃ crystal is a potential laser gain medium for solid-state laser and self-stimulated Raman laser applications. PACS 78.20.-e; 42.70.Hj     

Prompt isothermal decay of thermoluminescence in MgB4O7:Dy,Na and LiB4O7:Cu,In dosimeters

According to standard delocalized kinetic models of thermoluminescence (TL), when an irradiated sample is held at a high temperature T, the isothermal TL signal will decay with a characteristic thermal decay constant λ which depends strongly on the temperature T. This prediction of standard delocalized kinetic theory is investigated in this paper by studying two TL dosimeters, MgB₄O₇:Dy, Na and LiB₄O₇:Cu, In (hereafter MBO and LBO correspondingly). In the case of LBO it was found that the thermal decay constant λ of the main dosimetric TL peak follows exactly the predictions of standard delocalized kinetic theory. Furthermore, the thermal activation energy of the main peak evaluated by the isothermal decay method is in full agreement with values obtained from initial rise and glow curve fitting methods. However, in the case of MBO it was found that the thermal decay constant λ varies little with the isothermal decay temperature T. In order to explain these unusual results for MBO, the TL glow curves and isothermal decay curves were analyzed using analytical expressions derived recently from a radiative tunneling recombination model. Based on the different behavior of the two TL dosimeters, it is suggested that the isothermal decay of TL at high temperatures can be used to discriminate between radiative delocalized recombination and radiative localized recombination processes.