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Optical, luminescence and scintillation characteristics were studied in garnet-type GAGG single-crystal scintillators grown by the Czochralski method and heavily doped with a cerium activator and a magnesium codopant at different concentrations. Emission quenching due to the formation of closely spaced Ce-Mg pairs accelerating the photoluminescence and scintillation decays down to a few nanoseconds and substantial suppression of slower decay components are observed. We show that despite a significant decrease in the scintillation yield, the coincidence time resolution and the afterglow, which are the most critically important parameters of fast scintillators, exhibited by the heavily doped GAGG:Ce,Mg are superior to those in the state-of-the-art scintillators. Due to the peculiar feature of the GAGG host to tolerate extremely high cerium and magnesium concentrations while still maintaining a bulk single crystal form, this scintillator has a great potential for high-count-rate applications in high energy physics experiments and industries with harsh operational environments, where a lower light yield can be tolerated.

We report on a novel phosphoramide complex with formula Cu(NO3)2([C5H10N]3PO)2. This complex is the first example of a copper monomeric phosphoric triamide having an octahedral Cu[O]6 coordination environment. Cu(NO3)2([C5H10N]3PO)2 crystallizes in the monoclinic space group P21/n with the Cu atom located at an inversion center, as determined by single-crystal X-ray diffraction. Magnetic measurements along the principal crystallographic directions of the single crystal indicate that the complex is a paramagnet with very low magnetic anisotropy. Electron paramagnetic resonance spectra reveal the presence of two Cu2+ sites and make it possible to extract the hyperfine coupling.

The Tb3Ru4Al12 compound (hexagonal crystal structure) having a distorted kagome net of the Tb atoms is studied on a single crystal by measurements of magnetization, specific heat and electrical resistivity. The system is an antiferromagnet with the Néel temperature TN = 22 K. A substantial magnetic anisotropy is observed that persists at least up to 60 T. Tb3Ru4Al12 displays field-induced magnetic phase transitions: one along [100] and [120] and two along the [001] axis. The transitions are accompanied by sharp peaks in magnetoresistance and subsequently lead to a large negative effect in it, −20% in the longitudinal and −40% in the transverse geometry. The peaks are explained by changes in conduction electron spectra at the transitions due to the interaction between the conduction electrons and localized magnetic moments. The large negative effect suggests field-induced magnetic phases with a reduced period as compared to zero field.

Violet (1) and blue (2) polymorphous modifications of [Cu(men)2Pt(CN)4]n (men = N-methyl-1,2-diaminoethane) have been prepared and investigated by IR and UV–vis spectroscopy, thermal analysis, measurement of magnetic data and X-ray structural analysis. Both modifications are formed by similar but differently packed zigzag chains, which consist of [Cu(men)2]2+ moieties bridged by two trans arranged cyanido groups of [Pt(CN)4]2- units. The Cu(II) atoms in both structures are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate men ligands with the average Cu–N(Me) and Cu–N(H2) bond lengths of 2.046(8) and 2.008(8) Å, respectively, and by two nitrogen atoms from bridging cyanido groups in the axial positions at average distance of 2.50(7) Å. Broad nearly symmetric bands observed in the UV–vis spectra of 1 and 2 of 2B1g -> 2Eg transitions are consistent with a deformed octahedral coordination of the CuN6 chromophoric groups. One and two nu(C-N) absorption bands observed in the IR spectra of 1 and 2, respectively, are in agreement with different local symmetries of [Pt(CN)4]2- units and different Cu–N(cyanido) bond lengths in these polymorphs and are subject of discussion on the spectral–structural correlations in 1D compounds. The complexes are stable up to 238 °C when their two-stage thermal decompositions start and ending up with a mixture of CuO and metallic Pt as the most probable final thermal decomposition products. The temperature dependence of the magnetic susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) atoms in 1, J/hc = -0.17 cm-1 and in 2, J/hc = -1.3 cm-1.

info:eu-repo/semantics/published

info:eu-repo/semantics/published

We present an investigation of defects acting as electron traps in Lu 2SiO5 (LSO) and LuxY2-xSiO 5 (LYSO) performed by wavelength-resolved thermally stimulated luminescence (TSL) measurements from 20 to 400°C after room-temperature (RT) x-ray irradiation. Single crystals doped with several rare-earth ions such as Ce, Tb, Tm, and Sm were considered. A comparison between TSL and RT radio-luminescence (RL) emission spectra is also presented. The glow curves for both LSO and LYSO are similar, showing a series of TSL peaks at 78, 135, 181, and 236°C. In addition, a further peak at about 300°C is observed only in LYSO. Our results confirm the role of oxygen vacancies as electron traps in the material; the presence of several glow peaks with a unique trap depth (0.99eV±0.07 eV) for the 78, 135, 181, and 236°C peaks is explained by suggesting that electrons stored in oxygen vacancies recombine through a thermally assisted tunneling mechanism with holes localized at Ce3+ or Tb3+ centers residing on Lu sites at different crystallographic distances from the traps. This model is supported by the very good correlation among O-Lu distances in the monoclinic C2/c structure of LSO and LYSO and the frequency factors of the traps containing the transmission coefficients of the potential barriers between traps and centers, evaluated in the framework of the thermally assisted tunneling process. Tm and Sm ions do not act as TSL recombination centers possibly due to their tendency to trap electrons during irradiation with ionizing radiation. © 2008 The American Physical Society.

LiCaAlF6 (LiCAF) single crystals pure and doped with MgF2 and BaF2 were successfully grown by the Czochralski technique. Optical absorption measurements in the UV/Visible spectral regions following x-ray irradiation (radiation induced absorption) were performed in order to investigate the radiation damage of the crystals. The F-center absorption band at 262 nm is the dominating induced absorption feature. The amplitude of the F-absorption band is suppressed by more than a factor of 3 in Mg-doped LiCAF compared to undoped, while for Ba-doped LiCAF, almost no variation is obtained. In Mg-doped crystals the optimum doping concentration is of about 0.2 mol % of MgF2 in the melt. (C) 2002 American Institute of Physics.

A thermally stimulated luminescence (TSL) study in the temperature range 20-300 degrees C has been performed after x-ray irradiation on mixed LuxY1-xAlO3:Ce crystals (x=0.1-0.3) and on YAlO3:Ce. Several glow peaks have been detected, namely at 50 degrees C, 100-130 degrees C (composite structure), 175 degrees C and 225 degrees C, whose intensities are dependent upon the crystal composition. The spectrum of the emitted light features one band at 3.45 eV due to the 5d-->4f transition of the Ce3+ ion, in good agreement with the UV excited emission spectrum. A detailed analysis of the trap depths of the peaks has been performed in the case of Lu0.2Y0.8AlO3:Ce by partial cleaning of the glow curve. A constant energy value of approximately 1.15 eV has been found for all TSL peaks. From this result, and from the lack of a thermally stimulated current signal in the whole temperature range, it is possible to propose that TSL recombination is governed by a thermally assisted tunneling process from one trap level found at different distances from cerium emitting centers. A strong increase of TSL intensity has been observed after a prolonged annealing treatment in a vacuum atmosphere, suggesting that the electron traps are probably related to oxygen vacancies. Under this hypothesis, the relation between the frequency factors of the TSL peaks and the shortest O-Ce distances in the lattice has been investigated: an exponential dependence has been found, in accordance with what is expected for the thermally assisted tunneling recombination process.

Contains fulltext : 99025.pdf (publisher's version ) (Open Access)

Contains fulltext : 99022.pdf (publisher's version ) (Open Access)

Contains fulltext : 99025.pdf (publisher's version ) (Open Access)

Contains fulltext : 99022.pdf (publisher's version ) (Open Access)

Contains fulltext : 99022.pdf (publisher's version ) (Open Access)