Thermoluminescence of PbWO4 irradiated with UV light

PbWO4 single crystals were grown by the Czochralski method in argon and air. The glow curves induced by UV light and the absorption spectra of PbWO4 annealed at various temperatures were measured. The glow curves of PbWO4 were strongly dependent on the growing atmospheres. The activation energies of the 110 K peak of PbWO4 grown in argon and the 122 K peak of PbWO4 grown in air were calculated to be 0.23 eV and 0.29 eV, respectively. The ratio of the 2.76 eV emission band to the 2.48 eV or 2.26 eV emission bands of the PbWO4 grown in air was smaller than that of the PbWO4 grown in argon. The glow curve of PbWO4 grown in argon was similar to that of PbWO4 grown in air when the annealing temperatures were increased.     

Energy distribution of trapping and transport states in MDMO-PPV ([poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene)

We have investigated charge carrier transport and trapping in the layers of [poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene (MDMO-PPV). To reveal distribution of the trapping states the thermally stimulated current method was applied using the varying excitation conditions by light and applied voltage. To assure the selective excitation of the defect states close to the band gap edges, both extrinsic and intrinsic excitation by the light passed through the long-pass color filters with the cut-off energies ranging from 1.77 eV up to 3.1 eV was employed. Carrier transport conditions were varied by increasing applied electric field from 5 x 10(4) V/cm up to 6 x 10(5) V/cm. The effective thermal activation energy of material conductivity was dependent both on the spectral region of the exciting light and applied electric field. The superposition of several thermally activated processes, i.e., carrier generation from the trapping states and thermally stimulated mobility growth according to the Gaussian disorder model, was revealed. The energy distribution of the trapping state density was shown to follow the Gaussian distribution function. We had demonstrated that carrier trapping is effectively influenced by the extended defect states with the effective activation energy values ranging from 0.05 eV up to 0.15 eV with maximum located at about 0.07-0.08 eV. Moreover, deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.     

Morphological and structural modulation of PbWO(4) crystals directed by dextrans

A facile, dextran-directed solution route for the morphology-?and structure-controlled synthesis of PbWO(4) crystals, such as monoclinic raspite PbWO(4) nanobelts and tetragonal stolzite PbWO(4) crystals with penniform and wheat-ear-like morphologies, has been demonstrated. Three differently charged dextrans were employed for the PbWO(4) crystallization and they turned out to be very effective in the morphological and structural modulation of PbWO(4) crystals, as evidenced by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD) and Raman spectroscopy characterizations. In particular, novel monoclinic raspite PbWO(4) nanobelts were produced under the direction of anionic dextran with a suitable concentration, probably due to the specific interactions between SO(4)(2-) groups from anionic dextran molecules and Pb(2+) ions from PbWO(4) crystals. To the best of our knowledge, this is the first synthesis of monoclinic raspite PbWO(4) in the laboratory, which usually exists as a natural crystal. In addition, the photoluminescence properties of the obtained PbWO(4) crystals with different morphologies and crystal structures have been characterized and discussed, which provides useful information for the fundamental investigation and potential application of PbWO(4) crystals.     

熔体组成与PbWO4:Y3+晶体闪烁性能稳定性的关系

部分PWO：Y^3 晶体辐照后光产额升高，并且辐照硬度对退火温度较敏感。本文选取未掺杂及Sb、La^3 ,Y^3 单掺和La^3 /Sb,Y^3 /Sb双掺的PWO样品进行对照实验，同时选取代表性晶体的顶部急冷料做了X射线荧光主量分析。结果发现；低剂量辐射后光产额升高现象只存在于含Y^3 离子的PWO晶体中，并且这类晶体往往存在420nm吸收带；在改进Bridgeman法生长PWO晶体的后期，使熔体保持一定程度的负电性将有利于抑制该现象，即可有效地抑制同样是负电性的间隙氧进入晶体。结合测试数据，本文讨论了该现象的起因和机理，提出了掺杂剂的选择原则。     

Non-homogeneity of distribution of transport and trapping states in poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene

Carrier transport and trapping was investigated in poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) layers by thermally stimulated currents (TSC) depending on the exciting light spectral range. The upper edge of the spectra ranged from 1.77 eV up to 3.1 eV to assure selective excitation of the defect states. The TSC curves were shown to be a superposition of several thermally activated processes, i.e., carrier generation from trapping states and thermally stimulated mobility growth according to the Gaussian disorder model. The extrinsic excitation resulted in 0.15 eV photoconductivity effective activation energy values, which decreased down to 0.05 eV for the intrinsic excitation. The deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified too. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.     

钨酸铅(PbWO_4)晶体的发光均匀性研究

通过对下降法生长的全尺寸钨酸铅（ＰｂＷＯ４）晶体沿长轴方向不同点的透过率和光产额的测量、分段晶体的透过率和光产额的测量,研究了钨酸铅晶体的发光均匀性及其影响因素．结果表明：钨酸铅晶体发光均匀性主要由生长后期的钨酸铅晶体质量所决定,采用晶种为大头的加工取向有利于提高钨酸铅晶体的发光均匀性．     

The synthesis and photocatalytic activity of ZnSe microspheres

This paper reports the synthesis of semiconductor ZnSe microspheres composed of nanoparticles via a solvothermal route between the organic molecule selenophene (C(4)H(4) Se) and ZnCl(2) without adding any surfactant. The ZnSe microspheres were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), specific surface area measurement, and photoluminescence (PL) spectra. A strong and broad blue PL emission at 443 nm in wavelength (～2.79 eV in photon energy) is attributed to the near-band-edge (NBE) emission of ZnSe, while the 530 nm peak is a defect-related (DL) emission. The photocatalytic activity of the as-prepared ZnSe microspheres was evaluated by photodegradation of methyl orange (MO) dye under ultraviolet (UV) light and visible light irradiation. The degradations of MO reach 94% or 95.1%, close to 100%, in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 7 or 10 h under UV irradiation, respectively. Meanwhile the degradations of MO reach 94.3% or 60.6% in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 12 h, respectively. The degradation rate of ZnSe microspheres is twice that of ZnSe commercial powder under UV light irradiation, and three times under visible light irradiation. The degradation process of MO dye on ZnSe microspheres under UV or visible light is also discussed.     

Sonochemical synthesis of PbWO(4) crystals with dendritic, flowery and star-like structures

Lead tungstate single crystals with dendritic, flowery and star-like structures have been prepared via a facile, ethylene glycol (EG)-assisted sonochemical method. The concentrations of EG and ultrasound irradiation were found to play crucial roles in the morphology control of the final products. The growth process was investigated by carefully following time-dependent experiments, and the oriented attachment process accompanying Ostwald ripening was proposed for the possible formation mechanism. The optical properties, such as the Raman spectra and photoluminescence (PL) spectra, of the obtained PbWO(4) crystals were studied.     

钨酸铅晶体着色问题的实验研究

本计ＰｂＷＯ４（ＰＷＯ）晶体的着色问题进行了实验研究,以ＰｂＯ和ＷＯ３粉体为原料采用改进的Ｂｒｉｄｇｍａｎ法生长的ＰＷＯ晶体会呈现出浅黄色,通过对实验现象的分析,提出了ＰＷＯ晶体中同时存在Ｏ缺位和Ｐｂ缺位,其中,Ｏ缺位是导致ＰＷＯ晶体３５０ｎｍ率低的原因,Ｐｂ缺位是产生４２０ｎｍ吸收带使晶体着色的根源。     

X-ray absorption spectroscopy of PbMoO<Subscript>4</Subscript> single crystals

X-ray absorption spectra of PbMoO₄ (LMO) crystals have been investigated for the first time in literature. The measurements have been carried out at Mo absorption edge at the dispersive EXAFS beamline (BL-8) of INDUS-2 Synchrotron facility at Indore, India. The optics of the beamline was set to obtain a band of 2000 eV at 20,000 eV and the channels of the CCD detector were calibrated by recording the absorption edges of standard Mo and Nb foils in the same setting. The absorption spectra have been measured for three LMO samples prepared under different conditions viz. (i) grown in air from stoichiometric starting charge, (ii) grown in argon from stoichiometric starting charge and (iii) grown in air from PbO-rich starting charge. The results have been explained on the basis of the defect structure analysed in LMO crystals prepared under different conditions. The Mo absorption edge is significantly influenced by the deviations in crystal stoichiometry.     

Optical absorption, TL and IRSL of basic plagioclase megacrysts from the pinacate (Sonora, Mexico) quaternary alkalic volcanics

The paper presents the first results of an investigation on optical absorption (OA), thermally and infrared stimulated luminescence (TL and IRSL) of the Pinacate plagioclase (labradorite). The OA spectra reveal two bands with maxima at 1.0 and 3.2 eV connected with absorption of the Fe3+ and Fe2+ and IR absorption at wavelengths longer than 2700 nm. The ultraviolet absorption varies exponentially with the photon energy following the 'vitreous' empirical Urbach rule indicating exponential distribution of localised states in the forbidden band. The natural TL is peaked at 700 K. Laboratory beta irradiation creates a very broad TL peak with maximum at 430 K. The change of the 430 K TL peak shape under the thermal cleaning procedure and dark storage after irradiation reveals a monotonous increasing of the activation energy that can be explained by the exponential distribution of traps. The IRSL response is weak and exhibits a typical decay behaviour.     

Impurity band in in-doped CdCr2Se4 observed in the spectral dependence of the photoconductance

The spectral dependence of the photoconductance of In-doped CdCr₂Se₄ crystals was measured in the photon energy range from 0.2 eV to 2.5 eV. At a temperature of 80 K, i.e. below the Curie temperature of 132 K, two peaks of the impurity photoconductivity are observed. The peak energy of 0.38 eV agrees with the thermal activation energy determined from the slope of the ? vs T curves at higher temperatures. This agreement is an experimental evidence for the impurity band formed by the In donors and the Se vacancy donors which should be responsible for the large negative magnetoresistance due to “magnetic impurity states” in these crystals. At a temperature of 155 K, i.e. above the Curie temperature, the structure of the photoconductance vanishes due to the thermal activation of electrons from occupied donor levels to the conduction band.     

Amino acid 2-aminopropanoic CH3CH(NH2)COOH crystals: materials for photo- and acoustoinduced optoelectronic applications

Photo-induced treatment of l-alanine single crystals grown by slow evaporation method at an ambient temperature was performed using a 25 ps Nd:YAG pulsed laser in the presence of an external acoustic filed. The changes of the absorption were studied for the wavelength 265 nm near the energy band gap edge at acoustical power density varying within 4–6 W/cm². The observed absorption changes indicate that the external optical electric field strengths and acoustical power densities may be efficient parameters for the characterization of photo-optical and acousto-optical treatment of the samples. From the X-ray diffraction data we have optimized the atomic positions assuming that force on the atoms is around 1 mRy/au. These are used to calculate the electronic structure and the chemical bonding for the amino acid l-alanine single crystals. The calculated electronic band structure and densities of states confirms the experimental results that this compound possesses a relatively large energy band gap. The upper valence band has its maximum at the Z point of the Brillouin zone while the conduction band minimum is located at Γ point in the zone center, resulting in an indirect energy band gap. The electronic energy gap is equal to 4.19 eV within a framework of the used local density approximation and 4.54 eV with the Engel–Vosko generalized gradient approximation as the exchange correlation potential. This is in an agreement with our experimentally measured energy band gap ~4.67 eV. The existence of O-p character in the upper valence band has a significant consequence for the optical band gap. From our calculated electron charge density distribution, we obtain a space electron charge density distribution in the average unit cell of the crystal. The chemical bonding features of l-alanine amino acid were analyzed.     

Induced heating by nonlinear absorption in LiNbO3-type crystals under continuous-wave laser irradiation

We investigate light-induced heating by nonlinear absorption in LiNbO₃-type crystals under continuous-wave (CW) laser irradiation. The heat source is one-photon absorption by long-lived excited states created by two-photon absorption. The accumulated effect of excited states, which act as light absorbers, is significant for a CW laser. Light-induced heating causes catastrophic CW laser breakdown in LiNbO₃-type crystals in which the band-gap energy is less than twice the photon energy and in which long-lived excited states, like polarons, can exist. For LiNbO₃, the threshold intensity for catastrophic breakdown is estimated to be in the order of MW/cm².     

辐射防护用特种橡胶制品的制备与性能研究

一种新型γ射线防护用橡胶制品填充料由PbWO4和WO3复合制成，其组成为：WO3：PbWO4=40-60：60～40（质量分数）；制备方法：在分散剂、助剂存在下，由Na2WO4溶液与Pb（Ac）2溶液在快速搅拌下沉淀反应得到PbW04沉淀，然后将此PbW04沉淀加入到磨细的WO3浆体中，再研磨1～2h即成。该填充料与硫化橡胶乳液形成的分散系稳定性很好，制成的橡胶制品（手套）对59．5KeV的了射线的屏蔽率可迭15％～18％，抗拉强度达7．8～9．1MPa，断裂伸长率迭700～1000％；对产品中的Pb作迁移性检测，证明是符合安全卫生要求的。     

A study of vacancies and vacancy pair defects in 4H SiC grown by halide chemical vapor deposition

The understanding of the structure and associated defect level of a point defect in SiC is important because the material is to be used both as a semiconductor and semi-insulator. Production of the latter is achieved by compensation of unavoidable impurities using defects that require more energy for ionization than the unintentional donors or acceptors. The purpose of the present work is to measure the defect energy level of one center in high resistivity 4H SiC using photo-induced electron paramagnetic resonance (photo-EPR). The center is identified as SI-5, an EPR signal that others have attributed to the negative charge state of the carbon vacancy carbon antisite pair, $V_C C_{Si}^ - .$ The photo-threshold for detection of the signal is 0.75 eV in samples with resistivity activation energy, E_a, of 0.5 eV or smaller. For samples with larger E_a, SI-5 is detected only after irradiation with photon energy greater than 2.5 eV. The results suggest that $V_C C_{Si}^{ - - / - }$ is 0.75 eV below the conduction band edge and that the negative to neutral level is within 0.1 eV of $V_C C_{Si}^{- - / -} .$      

钨酸铅晶体生长及其组份挥发

本文首次报道了用坩埚下降技术生长钨酸铅（PWO）晶体;研究了提拉和坩埚下降两种技术生长PWO晶体的组份挥发,得到的结果是PbO的挥发速率高于WO₃,并对一组晶体不同部位的X射线发光性能作了研究．     

钨酸盐晶体中负离子配位多面体的结晶方位与晶体的形貌

钨酸盐类晶体是重要的闪烁晶体．本文从钨酸盐类晶体中负离子配位多面体的结晶方位和相互联结的稳定性出发，探讨了钨酸盐类晶体中[WO4]2-等负离子配位多面体的结晶方位与晶体结晶形貌之间的关系；认为[WO4]2-四面体与金属阳离子（Ca2＋，Pb2＋，Zn2＋）结合时，由于晶体结构和生长条件（如籽晶取向等）的不同，在晶体各族晶面上的叠合速率和结构取向不同，晶体的结晶形貌迥然有别；四面体的面和梭的法线（L2）所对向的晶面，生长速率慢，顽强显露，均属晶体的板面；四面体的顶角所指向的晶面，生长速率快，显露面积小，经常消失．由此可以合理解释钨酸铅等闪烁晶体的生长特征．最后对ABO4型晶体的结构及习性特征进行了总结归纳．     

Properties of Nd3+-doped and undoped tetragonal PbWO4, NaY(WO4)2, CaWO4, and undoped monoclinic ZnWO4 and CdWO4 as laser-active and stimulated raman scattering-active crystals

Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.