Perovskite Scintillators for Improved X-ray Detection and Imaging

Halide perovskites (HPs) recently have emerged as one class of competitive scintillators for X-ray detection and imaging owing to its high quantum efficiency, short decay time, superior X-ray absorption capacity, low cost, and ease of crystal growth. The tunable structure and versatile chemical compositions of halide perovskites provide distinguishable advantages over traditional inorganic scintillators for optimizing scintillation performance. Since the first observation of the scintillation phenomenon in HPs, substantial efforts have been devoted to expanding the inventory of HP scintillators and regulating material properties. Understanding the relationship between the structure and scintillation properties of HP scintillators is essential for developing materials with improved X-ray detection and imaging capacities. This review summarizes strategies for improving the light yield of HP scintillators and provides a roadmap for improving the X-ray imaging performance. Additionally, methods for controlling the light propagation direction in HP scintillators are highlighted for improving X-ray imaging resolution. Finally, we highlight the current challenge in HP scintillators and provide a perspective on the future development of this emerging scintillator.     

Eu2+掺杂KCaCl3晶体的生长及发光性能

通过坩埚下降法生长出不同物质的量分数Eu²⁺掺杂的KCa_1-xEu_xCl₃(x=0.005、0.01、0.02、0.03、0.05)单晶,并对晶体进行了X射线粉末衍射、热重、透过率、光致发光光谱、衰减时间、X射线激发发射光谱等测定。通过相图及结构分析,判断出该晶体为一致熔融化合物,并得出其为正交结构,晶胞参数为a=0.75604 nm,b=1.04823 nm,c=0.72657 nm,空间群为Pnma(62)。在紫外光的激发下,晶体在434 nm左右有一个宽的发射峰,对应于Eu²⁺的4f⁶5d¹→4f⁷跃迁;光致衰减时间1.473μs,晶体在X射线激发下的发光强度随Eu²⁺离子浓度增加而增强。     

Emergence of a Lanthanide Chalcogenide as an Ideal Scintillator for a Flexible X-ray Detector

The development of high-performance X-ray detectors requires scintillators with fast decay time, high light yield, stability, and X-ray absorption capacity, which are difficult to achieve in a single material. Here, we present the first example of a lanthanide chalcogenide of LaCsSiS₄ : 1 % Ce³⁺ that simultaneously integrates multiple desirable properties for an ideal scintillator. LaCsSiS₄ : 1 % Ce³⁺ demonstrates a remarkably low detection limit of 43.13 nGy_air s⁻¹ and a high photoluminescence quantum yield of 98.24 %, resulting in a high light yield of 50480±1441 photons/MeV. Notably, LaCsSiS₄ : 1 % Ce³⁺ exhibits a fast decay time of only 29.35±0.16 ns, making it one of the fastest scintillators among all lanthanide-based inorganic scintillators. Furthermore, this material shows robust radiation and moisture resistance, endowing it with suitability for chemical processing under solution conditions. To demonstrate the X-ray imaging capacity of LaCsSiS₄ : 1 % Ce³⁺, we fabricated a flexible X-ray detector that achieved a high spatial resolution of 8.2 lp mm⁻¹. This work highlights the potential of lanthanide chalcogenide as a promising candidate for high-performance scintillators.     

Single crystal growth and structure of La4Cu3MoO12

We report the synthesis and structure determination of single crystals of La₄Cu₃MoO₁₂ grown from a CuO/KCl flux. This material, whose structure had previously been reported based solely on polycrystalline diffraction data, shows frustrated magnetic behavior and an anti-ferromagnetic ordering of spin-1/2 triangles at low temperatures. The structural and atomic parameters determined from the single crystal data are in very good agreement with those reported previously. However, HREM data showed evidence for disorder in the stacking of the Cu₃MoO₄ planes, and thus a twinned structural refinement in space group P2₁/m was replaced by an equivalent disordered structural model in space group Pm. This development of a synthetic route to single crystals of La₄Cu₃MoO₁₂ will allow a more detailed investigation of its complex electronic and magnetic properties.     

Effect of refraction index and thickness of the light guide in the position-sensitive gamma-ray detector using compact PS-PMTs

We constructed a position-sensitive gamma-ray detector consisting of an array of BGO scintillators, a light guide and compact PS-PMTs. The effects of refractive index and thickness of the light guide of a glass plate on the detector performance were investigated. A light guide with higher refractive index and smaller thickness is found better for a good spatial resolution.     

Flux growth and magnetic properties of FeVO4 single crystals

FeVO₄ (I) single crystals are grown by the flux method using V₂O₅ as the self-flux. The grown crystals exhibit a characteristic morphology with natural facets. The quality of the crystals is confirmed by X-ray diffraction and EPMA techniques. Magnetic properties are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements. Two magnetic phase transitions are observed at ∼13 and ∼20 K. Such unusual magnetic behaviors are suggested to originate from two different Fe ligand environments of octahedral FeO₆ and trigonal bipyramidal FeO₅ in a six-column doubly bent chain.     

Yb3+共掺杂对Zn2GeO4∶Mn2+绿色长余辉发光性能增强研究

利用高温固相法合成了Zn2GeO4∶Mn2+以及Zn2GeO4∶Mn2+,Yb3+绿色发射长余辉发光材料,对样品进行了X射线衍射分析、荧光光谱分析、色坐标、热释发光以及发光寿命测量。分析结果表明,在1 050℃下烧结3 h的Zn2GeO4为单相产物,所得Zn2GeO4∶Mn2+发光材料具有良好的发光性能,在紫外灯激发下发出最强发射位于528 nm的宽带发射并具有优良的长余辉发光特性,其色坐标值分别为x=0.145,y=0.773。Yb3+共掺杂对其长余辉发光性能提高明显。余辉发光在暗场环境下肉眼可观察的持续时间超过2 h。通过热释光谱对陷阱进行了分析。对Yb3+共掺杂的长余辉发光增强机理进行了讨论。     

不同形貌Bi4Ti3O12粒子的可控合成及光催化性能

研究了用一步水热法制备的不同形貌的钛酸铋(Bi₄Ti₃O₁₂, BIT)粒子的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. XRD结果表明, 所制备的BIT 样品为层状钙钛矿结构. FESEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粒子. 紫外-可见漫反射光谱(UV-Vis DRS)表明BIT 样品的带隙能约为2.88-2.93 eV. 利用可见光(λ>420 nm)照射下的甲基橙(MO)降解实验评价了BIT 样品的光催化性能. 结果表明, BIT 的光催化活性比掺氮TiO₂ (N-TiO₂)高得多. 研究了形貌对BIT 光催化性能的影响. 所制备的BIT纳米带光催化效率最高, 经可见光照射360 min, 甲基橙溶液的降解率可达到95.0%.     

Transport coefficients of titanium-doped Sb2Te3 single crystals

Titanium-doped single crystals (c_Ti=0-2×10²⁰ atoms cm⁻³) were prepared from the elements Sb, Ti, and Te of 5 N purity by a modified Bridgman method. The obtained crystals were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 3-300 K. It was observed that with an increasing Ti content in the samples the electrical resistivity, the Hall coefficient and the Seebeck coefficient increase. This means that the incorporation of Ti atoms into the Sb₂Te₃ crystal structure results in a decrease in the concentration of holes in the doped crystals. For the explanation of the observed effect a model of defects in the crystals is proposed. The data of the lattice thermal conductivity were fitted well assuming that phonons scatter on boundaries, point defects, charge carriers, and other phonons.     

Latest developments of bulk crystals and thin films of rare-earth doped CaF2 for laser applications

Several CaF₂ single crystals doped with trivalent rare-earth ions have been grown in the recent years in the form of bulk crystals by using the Bridgman method and in the form of thin films by using the MBE and LPE techniques. The spectroscopic, gain and laser properties of these crystals doped with Pr³⁺, on the one hand, and with Yb³⁺, Tm³⁺ or Er³⁺ ions, on the other hand, have been studied and are reviewed here for their laser potentials in the red and in the infrared spectral domains, respectively.     

Design and Synthesis of Tb~(3+)-doped KGW Crystal for the Exploration of Scintillation Performance with X-ray Imaging

X-ray scintillators have been widely used in many fields owing to their strong penetrating ability,including security inspection, medical imaging, nuclear cameras, high energy physics and so forth. To explore new scintillation materials, we designed and synthesized KGW:Tb bulk scintillation crystals with monoclinic phase structure. We explored the fluorescence performance of KGW:Tb by testing the photoluminescence spectrum and fluorescence decay curve and observed strong green light emission in the visible light range at room temperature.Moreover, our crystal has a high stability under X-ray irradiation, a good sensitivity response and an appreciable light output(3424 ph/MeV) that is approximately twenty times more than PbWO_4. Moreover, we used a 0.98 mm thickness polished crystal sheet for X-ray imaging applications and observed excellent results. Therefore, KGW:Tb crystal may be an important direction for X-ray scintillation detection.     

Non-isothermal decomposition of Indian limestone of marine origin

Single crystals of pure and neodymium doped calcium hydrogen phosphate were grown in sodium meta silicate gels, by the single diffusion gel method. Platelet and needle shaped crystals were obtained. The grown crystals were characterized by different techniques. The thermal behaviour of the crystals was studied using the thermo analytical techniques, which included TG, DTA, DTG and DSC. These studies reveal that the decomposition of the material occurs in one or more stages. The enthalpy value is also calculated.     

Fabrication of Phosphorus-Doped Cobalt Silicate with Improved Electrochemical Properties

The development of electrode materials for supercapacitors (SCs) is greatly desired, and this still poses an immense challenge for researchers. Cobalt silicate (Co₂SiO₄, denoted as CoSi) with a high theoretical capacity is deemed to be one of the sustainable electrode materials for SCs. However, its achieved electrochemical properties are still not satisfying. Herein, the phosphorus (P)-doped cobalt silicate, denoted as PCoSi, is synthesized by a calcining strategy. The PCoSi exhibits 1D nanobelts with a specific surface area of 46 m²∙g⁻¹, and it can significantly improve the electrochemical properties of CoSi. As a supercapacitor’s (SC’s) electrode, the specific capacitance of PCoSi attains 434 F∙g⁻¹ at 0.5 A∙g⁻¹, which is much higher than the value of CoSi (244 F∙g⁻¹ at 0.5 A∙g⁻¹). The synergy between the composition and structure endows PCoSi with attractive electrochemical properties. This work provides a novel strategy to improve the electrochemical performances of transition metal silicates.     

State of the Art in Crystallization of LiNbO3 and Their Applications

Lithium niobate (LiNbO₃) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO₃ are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO₃, then the crystallization of LiNbO₃ single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO₃ and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO₃ crystals. The development of rare earth doped LiNbO₃ used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO₃ crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO₃ crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO₃ applications.     

Applications of neutron activation to microelectronic materials research at the Cornell TRIGA reactor

We present results from our use of neutron activation analysis (NAA) for the measurement and interpretation of the elemental content of materials being researched for applications in microelectronics. Examples include characterization of silicon-germanium and nickel silicide alloys, magnesium silicate crystals and ceramics for packaging of integrated circuits. High resolution delayed X-ray spectroscopy has been successfully employed as a complement to conventional gamma-ray analysis for determination of relative impurity concentrations. Fast neutron induced interferences are removed from gamma-ray spectra via the internal standard correction technique, based on the measurement of fast reaction rates.     

Optical and thermal properties of Fe3O4 nanoparticle-doped cholesteric liquid crystals

A composite system of Fe₃O₄ nanoparticle-doped cholesteric liquid crystals with properties of broadband reflection and controllable temperature under high-frequency electric field is proposed. The broadband reflection can shield the near-infrared light in summer and the electromagnetic-thermal effect by the Fe₃O₄ nanoparticles can deice or defrost in winter for high transmittance and good safety. Furthermore, the thermal effect may be precisely controlled and significantly enhanced by adjusting the factors of the doped concentrations and the applied electric field parameters (duration time, magnitude and frequency). This composite system may have potential applications for multifunctional windows of architectures and vehicles.     

The effects of fast neutron,gamma-ray and combined radiations on the thermal decomposition of ammonium perchlorate powder-aluminum particle mixtures

The thermal decomposition kinetics of irradiated and unirradiated ammonium perchlorate and ammonium perchlorate powder-aluminum particle mixtures has been studied by determining decomposition gas pressurevs. heating time with samples at a controlled temperature Qualitatively the radiation induced changes are similar to those obtained in previous studies on ‘pure’ ammonium perchlorate. The induction period is shortened and the acceleratory and decay period rate constants are increased. The data have been analyzed using Avrami-Erofeev kinetics. The results for pure unirradiated material are in accord with published results. The activation energies for the induction, acceleratory and decay periods for pure pellets were found to be 133.5±6.7, 131.8±6.7 and 127.2±6.7 kJ·mol, respectively. Samples were exposed to either a single gamma-ray irradiation, fission neutron irradiation followed by a gamma-ray irradiation, or to a proton irradiation. When compared on an equal energy deposited basis, the fast neutron induced changes are appreciably larger than the gamma-ray changes. However, the proton induced changes are comparable or slightly more than the gamma-ray effects. Some, or all, of the fast neutron effects can be attributable to the concentrated radiation damage ‘spikes’ along the path of lattice atom recoils. It is likely that these become thermal decomposition sites when the crystals are heated. Protons create fewer spikes than fast neutrons. Overall, the results indicate that any ammonium perchlorate-aluminum propellant mixtures that may be exposed to radiation environments, such as used in this study, should be subjected to a thorough radiation effects analysis if reliable performance is required. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Structure of TiO2 in TiO2-SiO2 prepared by a complexing agent-assisted sol-gel procedure

Many types of TiO₂-SiO₂ (Ti:Si=50:50 mol%) were prepared by the sol-gel procedure with and without 2-methyl-2, 4-pentanediol (MPD) as an organic ligand. The effect of MPD on the gel structure and the properties of the TiO₂ crystals were studied by XRD and raman spectroscopy, and the effect of the sol standing time on the properties of the TiO₂ crystals were also studied by XRD spectroscopy. In the gels with MPD, anatase of TiO₂ appeared at approximately 580°C, and the crystal structures were similar despite the difference in the gel preparation procedure. The titania gels with MPD were presumed to be dispersed in the silica gel matrix without any Ti-O-Si bond. In the presence of MPD, the formation of titania gels is controlled and the specified TiO₂ crystal is produced.     

Peculiarities in the Raman spectra of ZrB12 and LuB12 single crystals

We have measured Raman spectra of high-quality Zr^natB₁₂, Lu^natB₁₂ and Lu¹¹B₁₂ single crystals with high resolution, and the observed strong peaks are attributed to specific vibration modes. Besides, there are a number of additional Raman peaks in spectral ranges, where only Raman-inactive vibrations of the atomic arrangement are expected. Accordingly, it is assumed, that the investigated crystals contain intrinsic structural imperfections or distortions in sufficient concentration and efficiency to initiate the observed breaking of phonon selection rules. We suppose boron vacancies, boron isotope effects and displacements of the metal atoms to be reasons for such imperfections.     

NMR relaxation study of the phase transitions and relaxation mechanisms of the alums MCr(SO4)2·12H2O (M=Rb and Cs) single crystals

The physical properties and phase transition mechanisms of MCr(SO₄)₂·12H₂O (M=Rb and Cs) single crystals have been investigated. The phase transition temperatures, NMR spectra, and the spin-lattice relaxation times T₁ of the ⁸⁷Rb and ¹³³Cs nuclei in the two crystals were determined using DSC and FT NMR spectroscopy. The resonance lines and relaxation times of the ⁸⁷Rb and ¹³³Cs nuclei undergo significant changes at the phase transition temperatures. The sudden changes in the splitting of the Rb and Cs resonance lines are attributed to changes in the local symmetry of their sites, and the changes in the temperature dependences of T₁ are related to variations in the symmetry of the octahedra of water molecules surrounding Rb⁺ and Cs⁺. We also compared these ⁸⁷Rb and ¹³³Cs NMR results with those obtained for the trivalent cations Cr and Al in MCr(SO₄)₂·12H₂O and MAl(SO₄)₂·12H₂O crystals.