RESUMEN
Three novel bismuth-organic compounds, with the general formula [Bi2(HPDC)2(PDC)2]·(arene)·2H2O (H2PDC = 2,6-pyridinedicarboxylic acid; arene = pyrene, naphthalene, and azulene), that consist of neutral dinuclear Bi-pyridinedicarboxylate complexes and outer coordination sphere arene molecules were synthesized and structurally characterized. The structures of all three phases exhibit strong π-π stacking interactions between the Bi-bound PDC/HPDC and outer sphere organic molecules; these interactions effectively sandwich the arene molecules between bismuth complexes and thereby prevent molecular vibrations. Upon UV irradiation, the compounds containing pyrene and naphthalene displayed red and green emission, respectively, with quantum yields of 1.3(2) and 30.8(4)%. The emission was found to originate from the T1 â S0 transition of the corresponding arene and result in phosphorescence characteristic of the arene employed. By comparison, the azulene-containing compound displayed very weak blue-purple phosphorescence of unknown origin and is a rare example of T2 â S0 emission from azulene. The pyrene- and naphthalene-containing compounds both display radioluminescence, with intensities of 11 and 38% relative to bismuth germanate, respectively. Collectively, these results provide further insights into the structure-property relationships that underpin luminescence from Bi-based materials and highlight the utility of Bi-organic molecules in the realization of organic emission.
RESUMEN
We report on the detailed structural analysis of a series of 11 new quaternary rare earths containing thiosilicates, AkRE2Si2S8 (Ak = Ca and Sr; RE = La, Ce, Pr, Nd, Sm, Gd, and Tb), synthesized using the flux-assisted boron chalcogen mixture method. High quality crystals were grown and used to determine their crystal structures by single crystal X-ray diffraction. All members of the AkRE2Si2S8 series crystallize in the trigonal crystal system with space group R3Ì c (space group no. 167). Polycrystalline powders were used for physical property measurements, including magnetic susceptibility, diffuse reflectance in the UV-visible range, and scintillation. Magnetic measurements indicated that CaRE2Si2S8 (RE = Nd and Tb) exhibits paramagnetic behavior with a slightly negative Weiss constant. The band gaps of the materials were determined from diffuse reflectance data, and optical band gaps were estimated to be 2.5(1) and 2.9(1) eV for CaCe2Si2S8 and CaGd2Si2S8, respectively. CaCe2Si2S8, CaTb2Si2S8, and SrCe2Si2S8 exhibited intense green luminescence upon irradiation with 375 nm ultraviolet light and, furthermore, scintillated when exposed to X-rays. Radioluminescence measurements of CaCe2Si2S8 powder revealed green emission with an intensity approximately 14% of that emitted by bismuth germanium oxide powder.
RESUMEN
Proton radiography is a promising development in proton therapy, and researchers are currently exploring optimal detector materials to construct proton radiography detector arrays. High-density glass scintillators may improve integrating-mode proton radiography detectors by increasing spatial resolution and decreasing detector thickness. We evaluated several new scintillators, activated with europium or terbium, with proton response measurements and Monte Carlo simulations, characterizing relative luminosity, ionization quenching, and proton radiograph spatial resolution. We applied a correction based on Birks's analytical model for ionization quenching. The data demonstrate increased relative luminosity with increased activation element concentration, and higher relative luminosity for samples activated with europium. An increased glass density enables more compact detector geometries and higher spatial resolution. These findings suggest that a tungsten and gadolinium oxide-based glass activated with 4% europium is an ideal scintillator for testing in a full-size proton radiography detector.
RESUMEN
We report three novel Nb-containing oxide-fluorides, Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl, which were prepared as high-quality single crystals via a HF-based mild hydrothermal route. The compounds all crystallize in the trigonal crystal system with space group P3Ì m1. All three compositions form the same framework structure consisting of isolated [Nb2O2F9]3- dimers that create hexagonal channels that are occupied by disordered halide species. Upon excitation by UV light at room temperature, these compounds display broad band emission with a maximum at 440 nm for Cs10(Nb2O2F9)3F. The broad band emission of these compounds is attributed to the charge-transfer transitions of Nb-O bonds within the [Nb2O2F9]3- dimers. All three compounds scintillate blue under X-ray irradiation. Radioluminescence (RL) measurements performed on Cs10(Nb2O2F9)3F demonstrate that the RL emission intensity decreases with increasing temperature and that the integrated RL emission (300-750 nm) is 4% of Bi4Ge3O12 (BGO) powder. Thermogravimetric analysis confirms that Cs10(Nb2O2F9)3F has excellent thermal stability up to 600 °C and no structural phase transition is observed prior to sample decomposition.
RESUMEN
A series of new ternary lanthanide-based chlorides, Cs2EuCl5(H2O)10, Cs7LnCl10(H2O)8 (Ln = Gd or Ho), Cs10Tb2Cl17(H2O)14(H3O), Cs2DyCl5(H2O)6, Cs8Er3Cl17(H2O)25, and Cs5Ln2Cl11(H2O)17 (Ln = Y, Lu, or Yb), were prepared as single crystals via a facile solution route. The compounds with compositions of Cs7LnCl10(H2O)8 (Ln = Gd or Ho) and Cs5Ln2Cl11(H2O)17 (Ln = Y, Lu, or Yb) crystallize in a monoclinic crystal system in space groups C2 and P21/c, respectively, whereas Cs2EuCl5(H2O)10, Cs10Tb2Cl17(H2O)14(H3O), and Cs8Er3Cl17(H2O)25 crystallize in orthorhombic space groups Pbcm, Pnma, and P212121, respectively. Cs2DyCl5(H2O)6 crystallizes with triclinic symmetry in space group P1Ì . All of these compounds exhibit complex three-dimensional structures built of isolated lanthanide polyhedral units that are linked together by extensive hydrogen bonds. Cs2EuCl5(H2O)10 and Cs10Tb2Cl17(H2O)14(H3O) luminesce upon irradiation with 375 nm ultraviolet light, emitting intense orange-red and green color, respectively, and Cs10Tb2Cl17(H2O)14(H3O) scintillates when exposed to X-rays. Radioluminescence (RL) measurement of Cs10Tb2Cl17(H2O)14(H3O) in powder form shows that the RL emission integrated in the range of 300-750 nm was â¼16% of BGO powder.
RESUMEN
In order to decrease the generation of radioactive waste, it is of interest to develop a scintillator capable of absorbing tritiated solutions for efficient detection of low-energy ß-particles from tritium. In this work, paper scintillator incorporated with scintillator-silica fine powders (FPs), which is composed of scintillator-silica nanoparticles (NPs) attached to silica FP, was fabricated and evaluated. The scintillator-silica NPs contained liquid scintillators benzoic acid, 2,5-diphenyloxazole (PPO), and 1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP). Photophysical characterization was executed by means of photoluminescence, fluorescence lifetime, quantum efficiency, and radioluminescence under X-ray excitation. POPOP emission was confirmed by absorbing the emissions from benzoic acid and PPO. Radioluminescence results confirmed POPOP emission. Fluorescence lifetime analysis yielded a 1.29 ± 0.01 ns main fast decay (64.2%) combined with a 4.00 ± 0.04 ns slower decay (35.8%). The combined luminescence results suggested that most POPOP in the paper scintillator was solvated. At 301 nm, the average quantum efficiency from both faces of the paper scintillator was about 4%, and at 370 nm, it was about 11%. The paper scintillator detected 3H ß-particles by dipping the paper scintillator into tritiated water without a liquid scintillator. The counting efficiency depended on water content in the paper scintillator, and it increased to above 10% for tritium activity less than 200 dpm since it was preferentially adsorbed by vapor pressure isotopic effect and isotopic exchanged tritium on the surface of the scintillator-silica FP in the paper scintillator.
RESUMEN
Understanding the mechanisms of proton conduction at the interface of materials enables the development of a new generation of protonic ceramic conductors at low temperatures (<150 °C) through water absorption and proton transport on the surface and grain boundaries. Conductivity measurements under Ar-3% H2O and Ar-3% D2O revealed a σ(H2O)/σ(D2O) ratio of approximately 2, indicating a hopping-based mechanism for proton conduction at the interface. In situ Raman spectroscopy was performed on water-saturated, porous, and nanostructured TiO2 membranes to directly observe the isotope exchange reactions over the temperature range of 25 to 175 °C. The behavior of the isotope exchange reactions suggested a Grotthuss-type proton transport and faster isotope exchange reactions at 175 °C than that at 25 °C with a corresponding activation energy of 9 kJ mol-1. The quantitative and mechanistic kinetic description of the isotope exchange process via in situ Raman spectroscopy represents a significant advance toward understanding proton transport mechanisms and aids in the development of high-performance proton conductors with rapid surface exchange coefficients of importance to contemporary energy conversion and storage material development. In addition, new material systems are proposed, which combine interface and bulk effects at low temperatures (<150 °C), resulting in enhanced proton transport through interfacial engineering at the nanoscale.
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The present article focuses on the influence of gamma irradiation on nanoscale polymer grafted films and explores avenues for improvements in their stability toward the ionizing radiation. In terms of applications, we concentrate on enrichment polymer layers (EPLs), which are polymer thin films employed in sensor devices for the detection of chemical and biological substances. Specifically, we have studied the influence of gamma irradiation on nanoscale poly(glycidyl methacrylate) (PGMA) grafted EPL films. First, it was determined that a significant level of cross-linking was caused by irradiation in pure PGMA films. The cross-linking is accompanied by the formation of conjugated ester, carbon double bonds, hydroxyl groups, ketone carbonyls, and the elimination of epoxy groups as determined by FTIR. Polystyrene, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, dimethylphenylsilanol, BaF2, and gold nanoparticles were incorporated into the films and were found to mitigate different aspects of the radiation damage.