Search Results (36)

In this study, we developed and characterized novel scintillators with Ce: LiCaAlF₆–CaF₂–Li₃AlF₆ and Ce: CaF₂–LiF–Li₃AlF₆ ternary systems for thermal neutron detectors. The eutectics were grown by the vertical Stochbarger-Bridgman (VB) technique, and their constituent phases were identified using powder X-ray diffraction and scanning electron microscopy. Radioluminescence spectra irradiated under an Ag-target X-ray tube and confirmed the 5d-4f and self-trapped exciton luminescence derived from Ce³⁺. Scintillation decay and pulse height measurements were performed using ²⁵²Cf and ⁶⁰Co sources. The Ce: CaF₂–LiF–Li₃AlF₆ sample exhibited approximately 5.6 times higher effective neutron sensitivity compared with a Ce: LiCaAlF₆ single crystal. A favorable decrease in the neutron discrimination threshold level (Q_th) due to reduced γ-ray emission was observed. ⁶Li-enriched Ce: CaF-based scintillators hold potential for nuclear decommissioning applications. Full article

A BaF₂ single crystal co-doped with Er³⁺ and Yb³⁺ was grown by the vertical Bridgman technique and investigated for its optical and dielectric properties. Judd–Ofelt analysis yielded intensity parameters Ω₂ = 0.59, Ω₄ = 0.38, and Ω₆ = 0.27 (×10⁻²⁰ cm²), with a quality factor χ = 1.41, indicating strong radiative transitions. Under UV and near-UV excitation, emissions at 321, 405, 518, and 536 nm were observed, with radiative lifetimes ranging from 1.1 to 3.4 ms. A single dielectric relaxation process was identified, with activation energy of 0.58 eV and associated with trigonal NNN dipoles. The NNN dipole concentration was estimated at ~2.5 × 10¹⁸ cm⁻³. These results support the suitability of Er³⁺,Yb³⁺ co-doped BaF₂ crystals for luminescent and dielectric applications in advanced photonic materials. Full article

In this study, we report the growth and comprehensive spectroscopic analysis of TmF₃-doped CaF₂ crystals, grown using the vertical Bridgman method. The optical absorption and photoluminescence properties of both trivalent (Tm³⁺) and divalent (Tm²⁺) thulium ions were investigated. Optical absorption spectra in the UV-VIS-NIR range reveal characteristic transitions of Tm³⁺ ions, as well as weaker absorption bands corresponding to Tm²⁺ ions. The Judd–Ofelt (JO) formalism was applied to determine the intensity parameters Ω₂, Ω₄, and Ω₆, which were used to calculate radiative transition probabilities, branching ratios, and radiative lifetimes for the Tm³⁺ ions. The emission spectra showed concentration-dependent quenching effects, with significant emissions observed for the concentration of 0.1 mol% TmF₃ under excitation at 260 nm and 353 nm for Tm³⁺ ions and at 305 nm for Tm²⁺ ions. A new UV emission associated with divalent Thulium is reported. The results indicate that higher TmF₃ concentrations lead to increased non-radiative energy transfer, which reduces luminescence efficiency. These findings contribute to the understanding of the optical behavior of Tm-doped fluoride crystals, with implications for their application in laser technologies and radiation dosimetry. Full article

During the solidification process, microstructures are affected by the experimental conditions, the thermophysical characteristics of the alloy, and the type of grain-refining particles. Unidirectional solidification experiments were performed in a vertical Bridgman-type furnace to investigate the effect of the solidification front velocity on the solidified microstructure of a non-refined and refined Al-20%Cu alloy. The samples were solidified by rapidly increasing the sample velocity (v) range from 0.02 mm/s to 0.2 mm/s while maintaining an almost constant temperature gradient (~5 K/mm). As a result, despite changes in the solid/liquid front velocity along the sample, the microstructure of the non-refined alloys remained columnar. In the refined alloy, the columnar structure changed into an equiaxed structure at two different front velocities. Full article

A series of lithium niobate crystals co-doped with uranium and indium was successfully grown by the modified vertical Bridgman method for the first time. With increasing In³⁺ ion doping concentration, the segregation coefficient of uranium and indium progressively deviated from 1. The structural refinement indicated that uranium ions with high valence preferred to occupy the Nb sites in LN: In, U crystals. LN: In_2.0, U_0.6 achieved multi-wavelength holographic writing with diffraction efficiency comparable to commercial crystals LN:Fe_0.3, demonstrating a response time that was four times shorter than LN:Fe_0.3. XPS analysis was employed to investigate the valence states of In³⁺ ions in LN: In_2.0, U_0.6, in which uranium ions presented three valences of +4, +5 and +6. Furthermore, the ‘real threshold concentration’ of In³⁺ ions in LN: In, U was calculated using the Li-vacancy model, which is consistent with the results obtained from the experimental study of the OH⁻ absorption spectrum. Discussions on the photorefractive centers in LN: In, U are also provided. This study not only demonstrates the impact of doping In³⁺ ions on the growth of LN:U crystals, but also offers new insights into the photorefractive properties of LN in the visible band. Full article

The ³He gas is commonly used for the detection of thermal neutrons. However, with the depletion of ³He gas, there is a need to develop new solid scintillators for thermal neutron detection. Solid scintillators containing ⁶Li, which have large neutron capture cross-sections and a large amount of energy released by transmutation reactions, are commonly used as alternative candidates. However, only single-crystal scintillators are currently used, and their ⁶Li concentration is limited by their chemical composition. In this study, we designed, grew, and evaluated a new eutectic scintillator, Rb₂CeCl₅/LiCl, which can improve the ⁶Li concentration compared with single-crystal scintillators. Rb₂CeCl₅, which was selected as the scintillator phase, has excellent scintillator properties (light yield: 36,000 photons/MeV, decay time: mostly 24 ns, slightly 153 ns), and is less deliquescent than other halide scintillators. The crystal grown using the vertical Bridgman method exhibited a eutectic phase composed of Rb₂CeCl₅ and LiCl. The eutectic crystals exhibited Ce³⁺ 5d-4f emissions, with a peak between 360 and 370 nm. The Rb₂CeCl₅ phase was identified as the luminescent phase via cathodoluminescence mapping, and 16,000 photons/neutron of the light yield and 56.1 ns of the decay time were observed. This study indicates that the Rb₂CeCl₅/LiCl eutectic scintillator is a promising candidate for use in thermal neutron detectors. Full article

Oriented magnesium bicrystals with a 45°$⟨10\overline{1}0⟩$ asymmetrical tilt boundary were produced by directional solidification in a vertical Bridgman furnace. Employing a partition in the cylindrical mold led to unwanted crystallization on the contact surface with the growing interface, disrupting the desired growth conditions for the boundary. A modified setup with seed crystals placed side by side in a conical mold addressed the former issue and enabled the production of high-quality 56 mm × $\mathrm{\varnothing }$ 34 mm bicrystals. Due to the asymmetrical character of the boundary, the adjacent growing crystals witnessed unequal growth rates, with the basal-oriented crystal dominating the growth process. Plane strain compression experiments were carried out on bicrystalline samples extracted from the prepared bicrystal. The panoramic orientation mapping of large areas of several mm² revealed low-angle boundaries (5° misorientation) associated with the curved segments of the original asymmetrical tilt boundary. It also depicted heterogeneous lattice rotation near the grain boundaries. Full article

In this article, we discuss the preparation of organic 2-chloro-5 nitroaniline (2C5NA) crystals and their different kinds of physical, chemical, and mechanical properties. The vertical Bridgman approach was used to effectively produce the bulk organic 2C5NA crystal. To produce a good-quality bulk crystal, the shape, dimensions, and cone angle of the ampoule were optimized. Also, the temperature profile was set for the 2C5NA crystal. The growth atmosphere and the lowering rate were identified to obtain a homogeneous mixture of the compounds and initiate the nucleation process. Single-crystal X-ray diffraction (XRD), powder XRD, proton Fourier transform nuclear magnetic resonance (FT-NMR), and Fourier transform infrared investigations were used to confirm the crystal structure, molecular structure, and presence of functional groups in the formed crystal. The formed crystal has a monoclinic crystal structure with the space group P21/c, according to single-crystal XRD analysis. The thermal stability and kinetic parameters were examined using thermogravimetric analysis and differential thermal curves. From dielectric analysis, the electrical conductivity and dielectric behavior of 2C5NA were investigated with variations in frequency and temperature. The organic 2-chloro-5-nitroaniline crystal demonstrates that the indentation size effect is observed in the Vickers micro-hardness test, which was also carried out. Full article

CsCu₂I₃ crystal is a promising Cu-based halide material for scintillation detection. In this paper, Na⁺ ion-doped CsCu₂I₃ crystals with a size of ϕ12 mm × 50 mm were grown successfully using the vertical Bridgman method, and the properties were systematically investigated. CsCu₂I₃:Na crystals exhibit yellow light emission peaking at 575 nm and a large Stokes shift of 1.55 eV. Based on the results of the XRD and XPS, the Na⁺ was introduced successfully. The optical absorption spectra show that the band gap of CsCu₂I₃ crystals was narrowed when the Na⁺ was doped. The photoluminescence quantum efficiency (PLQY) is improved from 16.4% to 19.6%. Finally, the X-ray-induced afterglow, and scintillation (energy resolution, light yield and decay time) under a ¹³⁷Cs source were measured and discussed. These results illustrate that CsCu₂I₃:Na crystals have potential applications in the radiation detection field. Full article

The lead-free halide perovskite Cs₃Bi₂Br₉ is a promising semiconductor material for room-temperature X-ray detection due to its excellent properties. However, material purity and crystal quality still limit the use of Cs₃Bi₂Br₉ crystals as detectors. In this work, we present a highly efficient purification method using continuous vacuum extraction to sublimate BiBr₃ precursors for Cs₃Bi₂Br₉. Impurity analysis via inductively coupled plasma mass spectroscopy showed that the purification method successfully removed most of the impurities in BiBr₃ precursors and improved the purity by at least one order of magnitude. Centimeter-sized Cs₃Bi₂Br₉ single crystals were grown by the vertical Bridgman method. The improved properties after purification were confirmed by UV-Vis-NIR spectra, infrared transmittance, and current–voltage (I–V) measurements. The results showed that the average transmittance of Cs₃Bi₂Br₉ crystals significantly increased from 62% to 75% in the 0.5–20 μm spectral range. Additionally, the resistivity increased by nearly three orders of magnitude from 5.0 × 10⁹ Ω·cm to 2.2 × 10¹² Ω·cm, meaning the material will have low leakage currents and be suitable for developing applications for room temperature radiation detection. Full article

Crystal materials are prone to cracking during growth, which is a key problem leading to slow growth and difficulty in forming large-size crystals. In this study, based on the commercial finite element software COMSOL Multiphysics, the transient finite element simulation of the multi-physical field, including fluid heat transfer—phase transition—solid equilibrium—damage coupling behaviors, is performed. The phase-transition material properties and maximum tensile strain damage variables are customized. Using the re-meshing technique, the crystal growth and damage are captured. The results show the following: The convection channel at the bottom of the Bridgman furnace greatly influences the temperature field inside the furnace, and the temperature gradient field significantly influences the solidification and cracking behaviors during crystal growth. The crystal solidifies faster when it enters the higher-temperature gradient region and is prone to cracking. The temperature field inside the furnace needs to be properly adjusted so that the crystal temperature decreases relatively uniformly and slowly during the growth process to avoid crack formation. In addition, the crystal growth orientation also significantly affects the nucleation and growth direction of cracks. Crystals grown along the a-axis tend to form long cracks starting from the bottom and growing vertically, while crystals grown along the c-axis induce the laminar cracks from the bottom in a horizontal direction. The numerical simulation framework of the damage during crystal growth, which can accurately simulate the process of crystal growth and crack evolution and can be used to optimize the temperature field and crystal growth orientation in the Bridgman furnace cavity, is a reliable method to solve the crystal cracking problem. Full article

The spectroscopic and imaging performance of energy-resolved photon counting detectors, based on new sub-millimetre boron oxide encapsulated vertical Bridgman cadmium zinc telluride linear arrays, are presented in this work. The activities are in the framework of the AVATAR X project, planning the development of X-ray scanners for contaminant detection in food industry. The detectors, characterized by high spatial (250 µm) and energy (<3 keV) resolution, allow spectral X-ray imaging with interesting image quality improvements. The effects of charge sharing and energy-resolved techniques on contrast-to-noise ratio (CNR) enhancements are investigated. The benefits of a new energy-resolved X-ray imaging approach, termed window-based energy selecting, in the detection of low- and high-density contaminants are also shown. Full article

The single-crystal lithium hydride (LiH) generally grows in a gradient temperature region with the Bridgman method. A stable and appropriate temperature gradient is crucial in the crystallization process. In this paper, the temperature variation of single-crystal LiH growth is calculated by the finite element method (FEM). It is shown that the LiH compact melted entirely after heating to 750 °C at 10 °C/min in a dual-temperature furnace and holding for 2.4 h. The crystallization margin was 46.5 °C after holding for 5 h. The crystallization margin of LiH at the cone point, respectively, decreased to 33.7 °C, 28.6 °C, 25.6 °C, and 16.5 °C when the upper furnace was maintained at 750 °C, and lower furnace was cooled to 680 °C, 650 °C, 630 °C, and 550 °C, respectively. The optimal conditions for obtaining large size and high-quality LiH single crystals were predicted to be 630 °C at a lower-temperature-zone, 200 mL/min (cooling water flux), and 20 mm/h rise rate of the furnace. Based on the parameters of the above simulation, we synthesized LiH single crystal. X-ray diffraction (XRD) patterns showed that the LiH single crystal exhibited a (2 0 0) crystallographic plane at 44.5° with good chemical stability in air. Full article

Radiation detectors based on Cadmium Zinc Telluride (CZT) compounds are becoming popular solutions thanks to their high detection efficiency, room temperature operation, and to their reliability in compact detection systems for medical, astrophysical, or industrial applications. However, despite a huge effort to improve the technological process, CZT detectors’ full potential has not been completely exploited when both high spatial and energy resolution are required by the application, especially at low energies (<10 keV), limiting their application in energy-resolved photon counting (ERPC) systems. This gap can also be attributed to the lack of dedicated front-end electronics which can bring out the best in terms of detector spectroscopic performances. In this work, we present the latest results achieved in terms of energy resolution using SIRIO, a fast low-noise charge sensitive amplifier, and a linear-array pixel detector, based on boron oxide encapsulated vertical Bridgman-grown B-VB CZT crystals. The detector features a 0.25-mm pitch, a 1-mm thickness and is operated at a −700-V bias voltage. An equivalent noise charge of 39.2 el. r.m.s. (corresponding to 412 eV FWHM) was measured on the test pulser at 32 ns peaking time, leading to a raw resolution of 1.3% (782 eV FWHM) on the 59 keV line at room temperature (+20 °C) using an uncollimated ²⁴¹Am, largely improving the current state of the art for CZT-based detection systems at such short peaking times, and achieving an optimum resolution of 0.97% (576 eV FWHM) at 1 µs peaking time. The measured energy resolution at the 122 keV line and with 1 µs peaking time of a ⁵⁷Co raw uncollimated spectrum is 0.96% (1.17 keV). These activities are in the framework of an Italian collaboration on the development of energy-resolved X-ray scanners for material recycling, medical applications, and non-destructive testing in the food industry. Full article

High-quality pentacene-doped p-terphenyl bulk crystals were grown by the selective self-seeding vertical Bridgman technique (SSVBT). The lattice structure and crystal properties of the samples of different doping concentrations and their relations with p-terphenyl single crystals were tested and analyzed. The doping effects of pentacene doping at different concentrations in p-terphenyl molecular crystals are discussed. The powder X-ray diffraction, FTIR, and ¹H NMR studies show that no additional peaks (except for p-terphenyl) are observed in the spectra of two doped crystals. The results indicate that guest molecules appear as defects in the form of irregularly oriented molecules which do not significantly change the crystal structures. As the doping concentration increases, the average crystallite size decreases, and the crystallinity declines. The ultraviolet–visible absorption and fluorescence spectra show that with added pentacene molecules, the characteristic peak intensities decrease in the spectra owing to the p-terphenyl molecular transition. Meanwhile, characteristic peaks appear due to the pentacene molecular transition. Moreover, with the increase of doping concentration, the intensities of characteristic peaks of host molecules decrease continuously, and those of guest molecules increase accordingly. Full article