Hydrothermal synthesis and characterization of YVO4-based phosphors doped with Eu3+ ion

Nanocrystalline yttrium orthovanadate (YVO₄): Eu powders with different morphologies were synthesized in basic media by surfactant-assisted hydrothermal process. The structures and optical properties of products were investigated using the X-ray powder diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Results showed that pH value played a key role in the formation of products with different morphologies. The photoluminescence measurement showed that the samples with different morphologies exhibited different properties. The dependence between the fluorescence and the microstructure was discussed.     

SrHfO3材料的研究现状与进展

本文概述了近几年SrHfO3材料的研究进展,阐述了以SrHfO3为基质掺杂不同稀土离子的发光粉体、陶瓷、薄膜等材料的制备方法、各种性能特点。提出了尚需解决的问题,展望了其未来的发展前景。     

Photoluminescence of CaAlSiN3:Eu2+-based fine red-emitting phosphors synthesized by carbothermal reduction and nitridation method

In this research, we have presented the synthesis and characterization of the various Ca_1−xEu_xAl_0.76Si_1.18N₃ (x = 0.01 ∼ 0.1) red-emitting phosphors, which were successfully prepared by carbothermal reduction and nitridation (CTRN) method without the strict needs of high pressure. Here, raw materials were CaCO₃, AlN, Si₃N₄, Eu₂O₃, and C. In particular, C was considered as efficient and robust reducing agent. The influences of reaction temperature, holding time, C content, and Eu²⁺ concentration were investigated in the crystal phase compositions and photoluminescence properties of the as-prepared phosphors. Importantly, CaAlSiN₃:Eu²⁺-based red phosphors with interesting properties were obtained with reaction temperature at 1600 °C for 4 h by atmospheric N₂–10%H₂ pressure, and the C/O ratio of 1.5:1, respectively. The emission peak positions of as-prepared phosphors were red-shifted from 607 nm to 654 nm with Eu²⁺ concentration from 1 mol% to 10 mol%. Meanwhile the highest luminescence intensity was achieved with 2 mol% of Eu²⁺ concentration, which showed high external quantum efficiency up to 71%. Combining the phosphor blend of green-emitting β-sialon:Eu²⁺, yellow-emitting Ca-α-sialon:Eu²⁺, and red-emitting Ca_0.98Eu_0.02Al_0.76Si_1.18N₃ with a blue LED (light emitting diodes), warm white LED can be generated, yielding the color rendering index (Ra) of 93 at correlated color temperature (CCT) of 3295 K. These results indicate that CaAlSiN₃:Eu²⁺-based red-emitting phosphors prepared by facile CTRN are highly promising candidates for warm white LEDs.     

3D position readout from thick scintillators

A novel technique has been developed and tested for the three-dimensional measurement of position in SPECT-PET detectors. Results are presented for 2 and 20 mm thick NaI(Tl) planar crystals. In a plane of crystal, a coordinate resolution of about 1 mm (rms error) is demonstrated. The depth of interaction (DOI) is measured with an rms error of about 2 mm using light cone parameters.     

First-principles study of electronic and optical properties of Pbnm orthorhombic SrHfO3

The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO₃. The equilibrium lattice constants of Pbnm orthorhombic SrHfO₃ optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO₃ have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO₃ has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO₃ indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO₃.     

Specific features of 3-D detection arrays of plastic scintillators

This paper describes the 3-D array of scintillation detectors made of a plastic scintillator. Its operation is based on obtaining simultaneously the signal arrival time, spatial coordinates, and amplitude of scintillation signal produced in detection elements by radiation. Such arrays are capable of identifying and localizing neutron and gamma sources, discriminating signals from these sources, and reducing the background caused by gamma rays, cosmic-ray muons, and neutrons.     

热等静压烧结制备细晶粒Ce,Y:SrHfO3闪烁陶瓷

Ce:SrHfO₃陶瓷因具有高密度和高有效原子序数, 对高能射线具有很强的阻止能力。同时, Ce:SrHfO₃陶瓷还具有快衰减和高能量分辨率等优异的闪烁性能, 引起了研究人员的广泛关注。由于传统的烧结方法难以实现非立方结构Ce:SrHfO₃陶瓷的透明化, 本研究采用真空长时烧结和短时真空预烧结合热等静压烧结(Hot Isostatic Pressing, HIP)方法制备Ce,Y:SrHfO₃陶瓷。以金属氧化物和碳酸盐为原料, 1200 ℃下煅烧8 h可以获得平均粒径为152 nm的纯相Ce,Y:SrHfO₃粉体。1800 ℃真空烧结20 h获得平均晶粒尺寸为28.6 μm的不透明的Ce,Y:SrHfO₃陶瓷, 而两步烧结法可以制备光学透过率良好的Ce,Y:SrHfO₃陶瓷。本研究详细分析了陶瓷致密化过程中微结构的演变, 探究了预烧结温度对Ce,Y:SrHfO₃陶瓷密度、显微结构和光学透过率的影响。真空预烧(1500 ℃×2 h)结合HIP后处理(1800 ℃×3 h, 200 MPa Ar)所获得的Ce,Y:SrHfO₃陶瓷在800 nm处的最高直线透过率为21.6%, 平均晶粒尺寸仅为3.4 μm。在X射线激发下, Ce,Y:SrHfO₃陶瓷在400 nm处产生Ce³⁺ 5d-4f发射峰, 其XEL积分强度比商用锗酸铋(BGO)晶体高3.3倍, Ce,Y:SrHfO₃陶瓷在1 μs门宽下的光产额约为3700 ph/MeV。良好的光学和闪烁性能可以拓宽Ce,Y:SrHfO₃陶瓷在闪烁探测领域的应用。     

CeNi3-based Intermetallic hydrides

A hydride phase containing 5.0 H atoms per formula unit has been synthesized in the CeNi₃-H₂ system at a hydrogen pressure of 5 MPa and a temperature of 273 K. The hydride is very stable during storage in air, with no hydrogen release. Its lattice parameters have been determined by X-ray diffraction for different synthesis conditions.     

Two new cerium-doped mixed-anion elpasolite scintillators: Cs2NaYBr3I3 and Cs2NaLaBr3I3

We recently discovered that mixed-anion Br–I elpasolite scintillators, Cs₂NaYBr₃I₃: Ce and Cs₂NaLaBr₃I₃: Ce, have promising performance. Ce concentration of these compounds was optimized in terms of light yield. Cs₂NaLaBr₃I₃ with 5% Ce (by mole) has a light yield of 58,000 ph/MeV, and excellent energy resolution of 2.9% at 662 keV. It is better than both endpoint compounds of the Br–I solid solution. Cs₂NaYBr₃I₃ with 2% Ce doping shows energy resolution of 3.3% at 662 keV, despite a relatively modest light yield of 43,000 ph/MeV. Non-proportionality of the mixed Br–I compounds was measured using gamma ray sources ranging in energy from 14 keV to 835 keV.The electronic band gaps of undoped Cs₂NaLaBr₃I₃ and Cs₂NaYBr₃I₃ were determined from optical transmittance and absorbance measurements. The band gaps of the compounds are 4.4 ± 0.1 eV, and 4.3 ± 0.1 eV, respectively.The crystal structures of Cs₂NaLaBr₃I₃: Ce and Cs₂NaYBr₃I₃: Ce are tetragonal and cubic respectively. The high symmetry leads to fewer cracks during crystal growth and minimizes light scattering at grain boundaries. The ease of crystal growth is promising for the scale-up of the growth process to larger sizes.     

High-Z liquid scintillators containing tin

Two series of high-Z liquid scintillators have been developed and found to be useful for detection of X-rays and gamma rays in the energy range of about 4–200 keV. One type of solution is composed of pseudocumene (PC) as the solvent, 4,4″-di(5-tridecyl)-p-terphenyl as the scintillating solute, and tetramethyltin as the heavy-atom compound. A second type of solution contains a much faster but lower-yield solute, 4-bromo-4″-(5-hexadecyl)-p-terphenyl; the other components are the same. A tin loading of 22 weight percent in either of these solutions increases its sensitivity to 8 keV X-rays by a factor of 2.5 for a sample thickness of 1 mm.Well-resolved photopeaks were recorded for 122 keV gamma rays from ⁵⁷Co using solutions containing 28 and 49 weight percent tin.Several pulse parameters i.e., rise time, decay time, etc., of the radiation from solutions with and without added tin have been measured by exciting the solutions with pulsed electrons from a linac. The decrease in scintillation yield with increased tin loading was found to be proportional to dilution of the PC solvent. Moreover, decay times of the solutions were not affected by addition of tetramethyltin. Therefore, it is concluded that the heavy atoms do not actively quench the fluorescence from these solutions.     

Nanodosemeters based on gel scintillators

The feasibility of a nanodosemeter based on a liquid scintillator cocktail of four components (ethoxylated nonylphenol, pseudocumene, water and a lipophilic mixture) is studied. The dosemeter can work in distinct gel phases, for which the radioactive substance can be confined inside aqueous nanoscale structures of different size. For water volumes ranging 0-15%, it results in a gel with micelles of 4 nm radius. For water volumes ranging 30-50%, the resulting liquid-crystal gel contains nanostructures of approximately 20 nm radius. The low-energy electron emission arising from the decay of (3)H and (55)Fe is counted in a commercial liquid-scintillation counting spectrometer for both homogeneous and gel samples. The counting efficiency gap between the two phases is used to compute the average energy deposited inside the micelle.     

Modelling of composite neutron scintillators

Composite neutron scintillators consisting of neutron-insensitive fluorescent dopant particles (e.g. ZnS:Ag) embedded in a matrix material containing isotopes with high neutron cross sections that emit energetic charged particles (e.g. 6Li) are a popular method for neutron detection in a variety of applications. The size and volume doping fraction of the fluorescent dopant particles and the densities of both dopant particles and the matrix material determine the characteristics of the pulse-height spectrum of emitted light and the probability that capture of a neutron will result in scintillation. In this work, we characterise the effects of these parameters for ZnS:Ag particles in a lithiated glass matrix using a Monte Carlo simulation of composite neutron detectors that we have constructed.     

Protonic and oxygen-ion conduction in SrZrO3-based materials

Strontium zirconate-based materials have been studied as potential high-temperature protonic conductors. Yttrium for zirconium substitution, and lanthanum for strontium substitution were selected to demonstrate that changes in composition can be used as a tool to design the properties. At temperatures below about 900 ° C, both yttrium-doped and undoped strontium zirconate are mostly protonic conductors at oxygen partial pressures below about 1 Pa, and mixed ionic and p-type conductors at higher pressures. The main ionic contribution changes from mostly protonic to oxygen-ion conduction with increasing temperature, which may affect the performance of electrochemical devices. Yttrium for zirconium substitution enhances both the electronic and ionic conductivities. Lanthanum for strontium substitution suppresses protonic conduction and gives rise to mixed oxygen-ion and n-type conduction in reducing conditions.     

Preparation and properties of thick LaMnO3-based films

Thick (50 ±10 μm) La_1-xSr_xMnO₃ (x = 0.2, 0.4) and La_0.7Ca_0.3Mn0₃ films were prepared by screen printing, and their electrical properties were studied. The films were found to be close in magnetoresistance and resistivity to bulk materials     

Microstructure and thermophysical characteristics of PbTiO3-based ceramics

Precursor powders of a modified lead titanate-based ceramic material have been synthesized by two different chemical techniques and also by the conventional attrition milling method. The influence of powder processing techniques on the phase development, powder morphology and thermophysical behaviour of the material have been examined. The study shows that the above properties in this material are strongly dependent on the powder synthesis method as well as the thermal treatment of the precursor powders.     

Growth and characterization of strontium metaborate scintillators

The undoped and 0.5% Ce³⁺-doped strontium metaborate SrB₂O₄ single crystals has been grown successfully by micro-pulling down method with radio frequency (RF) heating system, and scintillation characteristics including optical properties and radiation response were studied for these crystals. The Ce³⁺-doped SrB₂O₄ crystal showed absorption band around 240–320 nm, which is corresponding to the 4f-5d transition of Ce³⁺. Intense emission band at 375 nm due to the Ce³⁺ 5d–4f transition was observed under ²⁴¹Am 5.5 MeV α-ray excitation. The scintillation decay time showed fast (50 ns) and slow (1430 ns) components ascribed to the Ce³⁺ 5d–4f transition and lattice defect in the crystal, respectively. The scintillation light yield of Ce³⁺-doped SrB₂O₄ was calculated to be about 1000 ph/n under ²⁵²Cf irradiation.     

Sol-gel elaboration and characterization of YAG: Tb3+ powdered phosphors

Pure and Tb³⁺-doped Y₃Al₅O₁₂ materials have been successfully synthesized from sol-gel based alkoxide precursors. Their formation process, structure and microstructure were examined by means of X-ray diffraction (XRD), thermal analysis combined with infrared spectroscopy (TG-IR / TDA), infrared spectroscopy (IR), scanning electron microscopy (SEM) and solid-state NMR study (²⁷Al MAS NMR). Pure highly crystalline YAG powders were obtained from 900°C. Laser induced luminescence spectra as well as decay times versus Tb³⁺ concentration were also studied. The well known ⁵D₃ → ⁵D₄ cross-relaxation and concentration quenching phenomena were observed. Decay times of the green emission (λ_em = 544 nm) were mainly found to be exponential with time constant lower than 5 ms. Finally, the optimal terbium concentration for the luminescence efficiency of YAG:Tb³⁺ powders was determined.     

Defect complexes in Re3+-doped magnesium sulphate phosphors

A series of magnesium sulphate phosphors MgSO4:RE3+,X ( RE = Dy, Tm, Eu and X = P, Mn) have been prepared and studied. Based on the experimental results of thermoluminescence (TL) emission spectra and dose responses studies, it is proposed that in these phosphors large defect complexes are formed, which include intrinsic imperfections and dopants. These defect complexes were formed in the course of preparation of phosphors and could be regarded as basic elements in the TL multi-stage processes. This defect model might be applicable to the most of TL materials.