Thermally stimulated luminescence of polycrystalline CdWO4 at low temperatures

CdWO₄ scintillator powders were produced via solid state reaction and investigated by thermally stimulated luminescence technique after UV irradiation. Under a heating rate of 0.1 K/s, the glow curve presented a superposition of peaks at low temperatures. Four peaks were identified below 80 K by partial heating method and their kinetic parameters were evaluated from the initial rise analysis. Measurements were also performed for heating rates of 0.05 and 0.2 K/s and allowed the kinetic study by peak position method. Surface effects due to the polycrystalline feature of the sample were investigated by comparing the results with those reported for CdWO₄ single crystals.     

Luminescence of ZnWO4 and CdWO4 thin films prepared by spray pyrolysis

Thin films of ZnWO₄ and CdWO₄ were prepared by spray pyrolysis and the structural, optical, and luminescence properties were investigated. Both ZnWO₄ and CdWO₄ thin films showed a broad blue-green emission band. The broad band of ZnWO₄ films was centered at 495 nm (2.51 eV) consisted of three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 540 nm (2.30 eV). The broad band of CdWO₄ films at 495 nm (2.51 eV) could be decomposed to three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 545 nm (2.28 eV). These results are consistent with emission from the WO₆⁶⁻ molecular complex. The luminance and efficiency for ZnWO₄ film at 5 kV and 57 μA/cm² were 48 cd/m² and 0.22 lm/w, respectively, and for CdWO₄ film the values were 420 cd/m² and 1.9 lm/w.     

Preparation, structures and photoluminescent enhancement of CdWO4-TiO2 composite nanofilms

For the first time, Cadmium tungstate (CdWO₄)-TiO₂ composite nanofilms on a glass substrate were prepared by means of the dip-coating technique, in which collodion was used as a dispersant and film-forming agent. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric and thermal analyses (TG/DTA), FTIR and photoluminescence (PL) methods, respectively. SEM and XRD characterization of these films indicated that CdWO₄ particles crystallized in a monoclinic wolframite-type structure whereas TiO₂ particles were Anatase phase; and both of them were well distributed in the nanofilms. FTIR spectra proved the presence of CdWO₄ on the nanofilms. Photoluminescent results showed that the emitting peak of CdWO₄ films blue shifted slightly relative to that of CdWO₄ crystal. Moreover, the PL intensity of CdWO₄-TiO₂ composite nanofilm was much higher than that of CdWO₄ nanofilm. We ascribed that the introduction of TiO₂ should be responsible for the PL enhancement.     

A model for the transition in the oxidation of zirconium-base alloys

At a weight gain of approximately 20 to 30 mg/dm² during the oxidation of zirconium-base alloys at reactor operating temperatures the oxidation rate accelerates. This is the so-called transition. A mechanistic model has been developed to describe the transition based on the growth and interconnection of small pores along the oxide-metal interface. Once the pores interconnect, coolant can reach the oxide-metal interface and oxidation accelerates. The model has been programmed and incorporated into the previously reported oxidation model. Good agreement has been obtained between the model predictions and experimental data.     

Synthesis and photoluminescence properties of aqueous CdWO4 quantum dots with WO6 luminescence center

Aqueous CdWO₄ QDs were synthesized by the reaction of CdCl₂ and Na₂WO₄ in the presence of mercaptoacetic acid (TGA) as capping reagent. The crystal morphology, particle size and its distribution of as-prepared products were characterized by transmission electron microscopy (TEM, SAED) atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), and photon correlation spectroscopy (PCS), respectively. Qualitative assays for functional groups on the QDs’ surface were measured by fourier transform infrared spectroscopy (FTIR). Photoluminescence properties of QDs were studied by photoluminescence spectroscopy (PL). The results showed that the single QD with diameter of about 8 ± 2 nm was single-crystal. The particle size distribution of QDs was normal. Infrared absorption bands of carboxylic group on the surface of CdWO₄ QDs were observed around 1610-1550 cm⁻¹ (nonsymmetrical vibration of -COO⁻) and 1400 cm⁻¹ (symmetric vibration of C-O). With reaction-time going, PL peak position shifted from 498 to 549 nm and intensity of PL increased first and then decreased. PL peak position of QDs was blue-shift compared with 570 nm WO₆⁶⁻ luminescence center of bulk CdWO₄.     

Photoluminescence and persistent luminescence properties of non-doped and Ti4+-doped Mg2SnO4 phosphors

Mg₂SnO₄ exhibits green photoluminescence and persistent luminescence, which originate from oxygen vacancies. When Ti⁴⁺ ions were doped, an interesting Mg₂SnO₄:Ti⁴⁺ phosphor with bluish white photoluminescence under ultraviolet irradiation and with green persistent luminescence was first obtained. Our investigation reveals that two emission centres exist in Mg₂SnO₄:Ti⁴⁺. The centres responsible for the green emission are considered to be the F centres (oxygen vacancies) and the blue centres are the TiO₆ complex. Trap clusters in the band gap with different depths, such as [Sn_Mg^‥—O_i^″], [Sn_Mg^‥—V_O^·], [Sn_Mg^‥—V_O^×] and Mg_Sn^″, correspond to the components at 85 ℃, 146 ℃ and 213 ℃ of the thermoluminescence curve.     

掺Bi钨酸镉单晶体发光特性的研究

用坩埚下降法(Bridgman)生长出了Bi离子掺杂的CdWO₄单晶.测定了晶体不同部位的吸收光谱、发射光谱和X射线电子能谱(XPS).Bi离子的掺入引起CdWO₄晶体的吸收边从345 nm红移到399 nm.在311 nm, 373 nm,808 nm和980 nm光的激发下,分别观测到中心波长为470 nm,528 nm,1078 nm和较弱的1504 nm四个不同发射带.Bi:CdWO₄单晶的XPS谱分别与Bi₂ 关键词： Bi离子 荧光光谱 X射线电子能谱 4单晶')" href="#">CdWO₄单晶     

Precipitate synthesis of BaMoO4 and BaWO4 nanoparticles at room temperature and their photoluminescence properties

The uniform BaMoO₄ and BaWO₄ nanoparticles (NPs) have been successfully synthesized by solution route – the direct precipitation of Ba(NO₃)₂ and Na₂MO₄ (M = Mo and W) in ethylene glycol under 24 h stirring. The XRD patterns and SEM images proved that the products were tetragonal structured BaMoO₄ and BaWO₄ with uniform round nanoparticles. Shape, average particle size and particle-size distribution of products were analyzed by TEM – showing the round nanoparticles with the average size of 31.52 ± 4.65 nm for BaMoO₄, and 59.77 ± 9.61 nm for BaWO₄. The room temperature photoluminescence (PL) indicated that the products have strong blue emission centered at 441 nm – excited with 280 nm wavelength for BaMoO₄ NPs, and strong violet emission centered 378 nm – excited with 344 nm wavelength for BaWO₄ NPs. These PL behaviors attributed the existence of intrinsic transitions in the [MO₄]^2-$[{\text{MO}}_4{]}^{2-}$ (M = Mo and W) tetrahedrons of their crystal lattices.     

Radiation effects on luminescent and structural properties of YPO4: Pr3+ nanophosphors

ABSTRACT

YPO₄ phosphors doped with trivalent ion Pr³⁺ were prepared by sol–gel method and treated with different doses of gamma radiation, from 0.25 MGy to 4 MGy. Effects of radiation on morphology, structure and luminescent properties were analyzed. Also, the influence of radiation on the change in the color of the samples was examined. The color efficiency of powders was evaluated by colorimetric analysis (CIE and L * a * b system). It has been observed that powders change color under the influence of radiation, i.e. they pass from white to pinkish red. Also, it has been determined that the radiation affects morphology change, as the particle size increases with increasing of the radiation dose. With the increase in the radiation dose, the emission intensity of samples decreases. The structure remains almost unchanged after irradiation, and the intensity constantly decreases with increasing of dose.     

纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱     

Electronic structure studies of the spinel CoFe2O4 by X-ray photoelectron spectroscopy

The spinel CoFe₂O₄ has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co_0.4Fe_0.6)[Co_0.6Fe_1.4]O₄, where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe²⁺ may be present in the powder sample. The Co 2p_3/2 peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co²⁺ in octahedral sites, tetrahedral sites and Co³⁺ in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition.     

On the isotope effect of Tc in squaric acid (H2C4O4)

The phase transition mechanism in squaric acid is reviewed from the viewpoint of the pressure dependence of the O—H—O bond length (2R). The two-dimensional pressure effect on T_c is extracted from the hydrostatic pressure behaviour by taking account of the uniaxial stress applied perpendicular to the layer planes. The result shows that if 2R(H₂SQ) is stretched to 2R(D₂SQ) the phase transition temperature 7^H _c of H₂SQ coincides with T^D _c of D₂SQ. This result supports the suggestion that the phase transition mechanism is of the order-disorder type.     

Synthesis and characterization of Mn-doped Zn2SiO4/SiO2 phosphor particles in core-shell structure

Manganese-doped zinc silicate (Zn₂SiO₄:Mn) is a kind of phosphor material that has a photo-luminescent (PL) and cathode-luminescent (CL) properties with intensive green light emission at 520 nm. The particles consisting of SiO₂@Zn₂SiO₄:Mn (SiO₂ core-Zn₂SiO₄:Mn shell) were synthesized via colloidal process and forced precipitation. After drying, the Zn/Mn precipitates were coated on the surface of SiO₂ particles. The Zn/Mn precipitates reacted with SiO₂ and transformed to Zn₂SiO₄:Mn by suitable calcination. The microstructure, crystalline phase, and luminescent characteristics of the products were studied. Besides, a CL device consisting of the core-shell powder was characterized.     

Luminescence in LiNaSO4:Eu phosphor

Abstract

LiNaSO₄: Eu is a recently discovered thermoluminescence dosimetry (TLD) phosphor which is more sensitive than the widely used CaSO₄:Dy. In this paper results are reported on TL glow curves, TL emission spectra and PL photoluminescence. These measurements help to understand the role of impurity and the mechanism of thermoluminescence in this phosphor.     

Luminescence of mercurylike impurities in single-crystal CdWO4 compounds

The processes of crystallization by the method of liquid epitaxy are studied for the first time for single-crystal films of CdWO₄ doped with the mercurylike ions Bi³⁺ and Pb²⁺, which can be used as thin-film components of combined scintillators for monitoring α- and β-activities. It is shown that in comparison with their solidcrystal analogs, the special features of these films consist in a longwave shift of the integral luminescence spectrum that is caused by high concentrations of the radiating complexes (V_Cd-WO₆) with hv_max=2.05–2.15 eV and the “distorted” complexes (WO₆)^* in them. It is found that in the case of luminescence of single-crystal films CdWO₄:Pb, radiation of mercurylike centers (PbO₆) prevails with hv_max=2.87 eV, while in luminescence of CdWO4, radiation of centers (BiO₆) with hv_max=2.16 eV and of complexes (V_Cd-WO₆). Institute of Applied Physics, Iv. Franko Lvov State University, 49, General Chuprynka St., Lvov, 290044, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 211–215, March–April, 1998.     

Study on the photovoltaic property of Cu4SnS4 synthesized by mechanochemical process

Photovoltaic property of Cu₄SnS₄ (CTS) is studied by employing a superstrate solar cell structure of Mo/CTS/In₂S₃/TiO₂/fluorine-doped tin oxide (FTO) glass for the first time. The CTS absorber layer was prepared by a combination of mechanochemical and doctor blade processes. The annealing effects on the structural, optical and electronic properties of the CTS absorber layer were investigated. The novel CTS absorber layer shows conversion efficiency as high as 2.34% under the standard AM 1.5 condition.     

Rotationally resolved electronic spectroscopy of a nonlinear carbon chain radical C6H4

Rotationally resolved electronic spectrum of the origin band in the 2A″-X2A″ transition of a nonlinear carbon chain radical C₆H₄⁺ has been recorded in the 604 nm region using cw cavity ring down spectroscopy. The radical was produced by a discharge through an acetylene-helium mixture in a supersonic planar expansion. The rotational structure has been analysed and precisely determined. A band having a-type prolate rotational structure has also been observed near 581 nm. By considering the results of ab initio calculations this band is assigned to a transition involving the excitation of the ν₁₂ fundamental in the upper 2A″ electronic state of the same C₆H₄⁺ isomer.     

Optical study of the phase transitions in LiKSO4

The birefringence of LiKSO₄ has been measured over the range 27–700°C. The change in birefringence with heating and cooling is seen to be very different. Observations have been made on domains in (001) and (100) plates near the phase transitions.     

Monochromatic blue-green and red emission of rare-earth ions in MgGa2O4 spinel

Pr³⁺-activated blue-green phosphor and Eu³⁺-activated red phosphor hosted in MgGa₂O₄ spinel have been prepared by a gel-assisted high-temperature calcination process, respectively. Both anion and cation vacancies in the host were formed by decreasing the Mg concentration in the reaction source. The induced vacancies provide possibility of the accommodation of the doped rare-earth ions with larger atomic size in the highly symmetrical spinel structure. Due to the efficient energy transfer from the spinel host to the sole 4f sub-level of the doped rare earths, monochromatic emissions with high efficiency can be obtained to allow the phosphors to find applications in solid-state laser device and other phosphors excited under low energy. The corresponding spectroscopic transition mechanism has been proposed in this work.