Synthesis, growth and doped properties of PbWO4 crystals

High purity polycrystalline PbWO₄ (PWO) has been synthesized by a chemical method. Pure and doped PWO crystals were grown by using a Czochralski technique. Transmittance spectra, light yield and decay constants of the crystal were measured. The effect of PWO crystal quality and doped ions on its scintillating properties is discussed in this paper.     

Growth of trivalent ions doped PbWO4 crystals and their scintillation properties

Undoped and series of trivalent ions(including La, Y, Gd and Tb) doped PWO crystals were grown from 5N raw materials by using Czochralski technique. Trivalent ions doping improved the transmittance, fast components of luminescence and radiation damage resistance for compensating structure defects. Corresponding, the fraction of light yield at shorter collecting time was increased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of trivalent ions codoping on the Mo:PbWO4 luminescence properties

Trivalent ions codoping Mo:PWO boules were grown along the c-axis using the Czochralski technique. Trivalent ions codoping improved the fast components of luminescence for Mo:PWO due to suppression/compensation of hole-trapping centers. Correspondingly, trivalent ions codoping increased the fast components of the light yield. The La³⁺ and Gd³⁺ concentration in the crystal gradually decreased along the growth direction because they increased the melting point. The Y³⁺ concentration increased along this direction due to the different influence on the melting point. Compared with La:Mo:PWO, Y:Mo:PWO shows a more uniform transmittance along the growth direction.     

钨酸铅闪烁晶体垂直梯度凝固法生长及光学性能研究

本文报道了垂直梯度凝固法(VGF)生长PWO晶体的研究结果.通过优化工艺参数,成功获得直径25mm、长度140mm的PWO晶体.通过测试PWO晶体的XRD、透过光谱、荧光光谱等,研究了所得晶体的光学性能.结果表明:VGF法生长PWO晶体在350～420 nm处的光学透过率明显提高,荧光发光主峰位于435 nm,是快发光峰,但慢发光比例有所增加.     

Growth and properties of dyed KDP crystals

Potassium dihydrogen phosphate (KDP) crystals doped with xylenol orange (XO) and methylthymol blue (MTB) are grown from aqueous solutions by the method of solvent evaporation at room temperature under the conditions of natural convection and by the method of temperature lowering. Studied is the influence of the mother solution acidity on the character of the crystal coloration. The color and coloration intensity of the grown crystals are shown to strongly depend on the solution's pH. It is revealed that the crystal habit changes in the presence of organic dyes. The optical transmission spectra and the luminescence spectra of KDP:XO solutions and of the grown crystals are measured. The effect of thermal treatment and UV‐irradiation on the coloration stability of the crystals is studied. It is found that the laser damage threshold in the prismatic impurity rich colored sectors of KDP:XO is the same as that in the prismatic sectors of pure KDP crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Growth and characterization of Bis Thiourea Zinc Acetate (BTZA)

Single crystals of BTZA have been grown by low temperature solution growth method using slow cooling process at an optimized pH of 3.5. The grown crystals have been examined under an optical microscope to study its surface morphology. The morphological studies show that the growth takes place by spreading of growth layers. Formation of rectangular shaped etch pit on the as‐grown crystal has been explained in relation to the growth conditions. Single crystal X‐ray diffraction analysis has been carried out to confirm the monoclinic system. Transmission spectrum reveals that the crystal has a low UV cut off of 434.5 nm and has a transmittance of 100%. Dependence of micro hardness on load has been studied. Powder X‐ray Diffraction and FT‐IR have been carried out to characterize the grown crystals. BTZA forms metal – sulfur bond and has good optical transmission in the entire visible region, which is the essential requirement for a non‐linear crystal. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnesium-doped potassium lithium niobate crystal and its properties

High quality magnesium-doped potassium lithium niobate (designated as KLN:Mg) single crystal was grown for the first time. The tetragonal tungsten bronze structure of the Mg:KLN crystal was determined by X-ray powder diffraction, in which the lattice parameters were A=1.262nm and C=0.398nm. High temperature X-ray diffraction patterns showed that the expansion of the lattice with increasing temperature was less than that of the undoped crystal. The transmittance of the as-grown crystal was measured. It increased by 80% from the cutoff wavelength 380nm to 450nm. The transmittance for 404nm was 50%, which is larger than that of the undoped crystals. The frequency-doubling property of KLN crystal was analyzed. Preliminary frequency doubling experiments showed that the crystal could generate blue light of 404nm through noncritical phase matching (NCPM) second harmonic generation (SHG) using a 808nm diode laser at room temperature.     

Growth and characterization of cadmium magnesium tetra thiocyanate crystals

Cadmium Magnesium Tetra Thiocyanate, CdMg(SCN)₄, [CMTC] belongs to bimetallic thiocyanate complexes. CMTC crystals has been grown by solution growth technique at room temperature. The morphologies of the grown crystals are identified by single crystal analysis. Also the Powder X‐ray Diffractogram of the crystal has been recorded and the various planes of reflection are identified. The title compound crystallizes under triclinic structure with lattice parameters a = 10.0976 Å, b = 7.5015 Å, c = 5.7720 Å and β = 90.2135°. The presence of magnesium and cadmium in the grown crystals were confirmed through Atomic Absorption Spectroscopy. The grown crystals are analysed qualitatively by Fourier Transform Infrared (FTIR) and Fourier Transform Raman spectral measurements. The transmittance spectrum of the crystal in the UV‐Visible region has been recorded and analysed. The dielectric measurements for the crystals were carried out in the microwave region. The thermal stabilities of the crystals were studied by using different thermal analyses like Thermo Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

大尺寸PWO:(Mo,Y)晶体发光均匀性的研究

报道了用改进的Bridgman法生长的大尺寸PbWO4:(Mo,Y)晶体发光均匀性的表征研究.通过对大尺寸的PbWO4:(Mo,Y)晶体不同部位的透射光谱、X射线激发发射光谱、光产额和抗辐照损伤能力等光学和闪烁性能的测试,结果表明在实验所涉及的掺杂浓度范围,Mo、Y双掺杂能显著改善PbWO4晶体的发光均匀性,增强其抗辐照损伤能力.     

基于铈钆共掺杂YAG单晶荧光片的高光效白光LED

为了满足高功率白光发光二极管(Light-Emitting Diode,LED)对荧光体的高性能要求,对白光LED用Cex Gd:YAG单晶荧光材料的制备和光学、电学、热学特性进行了研究.采用提拉法生长了CexGd:YAG(x=0.02,0.04,0.06,0.08)单晶,并借助于X射线衍射(XRD)、吸收光谱、发射光谱等对晶体的光谱特性进行了表征,同时也测试分析了相对荧光强度随温度的变化关系、基于不同Ce3+浓度Cex Gd:YAG单晶的白光LED性能参数.结果表明Cex Gd:YAG单晶在450 nm的蓝光激发下,产生一个500～650 nm的宽峰发射,在100℃高温下,其荧光光强比商用荧光体粉末高出10;.当Ce3+浓度为6;时,采用Cex Gd:YAG单晶荧光片的白光LED光效高达153 lm/W,是Ce:YAG和树脂荧光材料白光LED的两倍多.Cex Gd:YAG单晶荧光片,具有更高更稳定的荧光光强,制作的白光LED光效有明显提升,有望成为新型的商用荧光体.     

Study on PbWO4 doped with Y, Sb

A series of PbWO₄(PWO) powders, undoped and doped with Y and or Sb, were prepared in air and studied by cathodoluminescence, photoluminescence excitation and emission spectra, and compared with that of undoped and Sb doped PWO single crystals grown by the Bridgman method. The luminescence of PWO prepared in air at high temperature (900° C) is mainly in a broad green band, and its intensity of emission is stronger than that of doped PWO. However the luminescence of PWO:Sb prepared in an oxygen deficient atmosphere is better than undoped PWO.     

Energy transfer and annealing behavior of luminescence in Dy-doped PbWO4 single crystal

The Dy³⁺: PWO single crystal was subsequently annealed in air atmosphere at a temperature of 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, and 1000°C, respectively. X-ray excited luminescence spectra were measured before and after each step of annealing. Annealing experiments confirmed the energy transfer-taking place from PbWO₄ (PWO) host to Dy³⁺ ions, followed by the enhancing characteristic emission of Dy³⁺ ions. In the process of annealing, the luminescence of PWO host was significantly reduced while that of Dy³⁺ was increased simultaneously. Annealing at a temperature below 700°C suppressed the blue luminescence of the PWO host and enhanced its green components, while the emission of Dy³⁺ is increased to some extent. Further annealing at higher temperature strongly reduced the luminescence of the PWO host, while the emission of Dy³⁺ was greatly increased. Interstitial oxygen O_i could play an important role in the luminescence. Annealing could modify the luminescence of Dy³⁺ ions in PWO, which may be useful in terms of some application purposes.     

Growth and characterization of semicarbazone of cyclohexanone

A new organic single crystal of semicarbazone of cyclohexanone (SCCH) has been synthesized and grown as a bulk single crystal by low temperature solution growth technique for the first time in the literature. The grown crystal has been confirmed by X‐ray diffraction and proton nuclear magnetic resonance spectral analyses and also characterized by FT‐ir and FT‐Raman studies. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. Optical transmittance was studied by ultraviolet‐visible spectrum and the second harmonic generation property was tested by using Q switched Nd: YAG laser as a source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of pure and urea-doped γ-glycine single crystals grown by solution method

Pure and urea-doped gamma-glycine (γ-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in γ-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV-visible transmittance studies were performed to analyse optical transparency of pure and urea-doped γ-glycine crystals and found that the crystals were transparent in the entire visible-NIR region. Density and melting point of the grown crystals were measured. Second harmonic generation (SHG) for the grown crystals of this work was confirmed using Nd:YAG laser. Thermogravimetric and differential thermal analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. From Microhardness studies, it is observed that urea-doped γ-glycine crystal is harder than pure (undoped) sample.     

Structural,thermal and optical studies on 2‐naphthol crystals

Single crystals of 2‐naphthol was grown in slow evaporation solution growth technique. Grown crystals were characterized by various characterization techniques. Powder X‐ ray diffraction studies reveal that the grown crystal belongs to monoclinic system with noncentrosymmetric space group. Vibrational bands of the various functional groups and their significance were investigated by analyzing the vibrational spectra. Melting point and the decomposition temperature of the grown crystal was premeditated from the thermal analysis. From the UV‐VIS‐NIR spectrum the electronic excitation mechanism and the transmittance abilities of the crystal was studied. Theoretical value of first static hyperpolarizability was calculated and compared with urea. Second harmonic generation efficiency of the crystal is 0.6 times that of KDP. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

*Ir4+ ion‐free 12CaO·7Al2O3 single crystal grown by the CZ method

Ir⁴⁺ ion‐free 12CaO•7Al₂O₃ (C12A7) single crystals that were colorless and transparent have been grown by the CZ method under 0.5% oxygen‐containing nitrogen atmospheres for the first time. Powder X‐ray diffraction patterns and X‐ray single‐crystal diffraction were used to investigate the microstructure and quality of the C12A7 single crystal. The results show that the crystal was a C12A7 single crystal with tetragonal symmetry. The content of Ir⁴⁺ in the C12A7 single crystal was tested by ICP along with visible‐light transmittance. There was no Ir⁴⁺ in the C12A7 crystal grown in a 0.5% oxygen‐containing nitrogen atmosphere. Contents of Ir⁴⁺ in C12A7 crystal grown under 1% and 2% oxygen‐containing nitrogen atmospheres were 500 ppm and 400 ppm, respectively. The microstructure of C12A7 single crystal was determined by the content of oxygen in the growth process: the occurrence of bubbles and color increase when the content of oxygen is increased. Bubbles and color decrease when the oxygen content is lowered, bubbles disappeared and the color of C12A7 turns into transparent when the content of oxygen is 0.5%, the C12A7 phase decomposed when the content of oxygen was lower than 0.5%. So, the content of oxygen was responsible for the bubbles, color and cracking, and these also can be limited by controlling the content of oxygen.     

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)     

Effect of different solvents on the habit of meta‐nitroaniline single crystals

The habit of the organic non‐linear optical material meta‐nitroaniline (mNA) crystallized from different organic solvents such as acetone, benzene, ethyl acetate, n‐hexane, methanol and toluene were studied. Solubility of mNA in these solvents at various temperatures in the range between 288 and 323 K was determined by gravimetric method. Crystals were grown by restricted evaporation of solvents method. Solutions with different solvents having different chemical nature and polarity yielded crystals with different habits: one‐dimensional needles, two‐dimensional rhombic platelets and three‐dimensional octahedral. In addition, the mNA crystals show unidirectional growth behaviour along its polar [001] direction irrespective of the solvents used. All the grown crystals were found to be orthorhombic system with point group mm2 and space group Pbc2₁ which was confirmed by powder X‐ray diffraction study. Optical transmittance study showed that the grown mNA single crystals have optical transparency in the wavelength range between 430 and 1550 nm. SHG efficiency of the grown mNA crystal was 3 times grater than KDP. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of thermally evaporated CdS thin films

CdS thin films of varying thicknesses were deposited on cleaned glass substrates at room temperature by thermal evaporation technique in a vacuum of about 2 x 10^‐5 torr. UV‐VIS spectra of the films were studied using the optical transmittance measurements which were taken in the spectral region from 300 nm to 1100 nm. The absorbance and reflectance spectra of the films in the UV‐VIS region were also studied. Optical constants such as optical band gap, extinction coefficient, refractive index, optical conductivity and complex dielectric constant were evaluated from these spectra. All the films were found to exhibit high transmittance (∼ 60 ‐ 93 %), low absorbance and low reflectance in the visible/near infrared region from ∼ 500 nm to 1100 nm. The optical band gap energy was found to be in the range 2.28 – 2.53 eV. All the films annealed at 300°C for 4 hours in vacuum (∼ 10^‐2 torr) showed a decrease in the optical transmittance with its absorption edge shifted towards the longer wavelength, leading to the result that the optical band gap decreases on annealing the films. Also, on annealing crystallinity of the films improves, resulting in decrease in the optical transmittance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)