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Photostimulated luminescence phosphors are promising candidates for next‐generation optical data storage devices. Herein, optically‐reversible luminescence modulation is demonstrated using UV wavelengths in the fluoroperovskite RbCdF3:Mn, where the modulation is mediated by photostimulated luminescence processes. UV‐C stimulation enhances the luminescence from Mn2+ centers and simultaneously fills electron traps. This charging process occurs via electron transfer from Mn2+ ions to fluorine vacancies, yielding Mn3+ ions and F‐centers, and is mediated by conduction band transport. UV‐A stimulation restores the material to the initial state. This discharging process occurs via electron transfer from F‐centers to Mn3+ ions and is similarly mediated by conduction band transport. Moreover, the discharging process manifests Mn2+ photostimulated luminescence. The primary trap state has activation energies in the range 1.46 to 1.73 eV and has room temperature lifetimes exceeding 40 000 years. A kinetic model is presented and evaluated that accurately describes the charge transport and luminescence properties of the material. Thus, a material is presented via which ultra‐long term, multi‐level luminescent data storage can be realized, and a model via which precise control over the luminescence modulation and photostimulated luminescence intensities can be achieved. [ABSTRACT FROM AUTHOR]

We report the results from a comprehensive study of the effect that annealing FeSe0.35Te0.65 single crystals in different atmospheres has on the surface chemistry, the superconducting transition temperature, Tc, and the critical current density, Jc. A review of the literature and our data shows that annealing in oxygen, nitrogen, air or vacuum atmosphere leads to a universal superconducting phase diagram that is independent of the variance in the as-grown properties. We show that atmospheres with an oxygen partial pressure of p > 10−3 hPa during annealing are necessary to improve the superconducting properties in this compound. This is demonstrated by Raman and magnetisation measurements on air, nitrogen, or low vacuum annealed FeSe0.35Te0.65 samples, which show that the improvement in the superconducting properties is strongly correlated to the formation of a thin iron oxide surface layer. However, annealing under high vacuum does not lead to the formation of an iron oxide layer and no improvement in the superconducting properties is observed. Our findings show that the previously reported improvements in the superconducting properties after annealing under vacuum or in nitrogen are thus likely to have been caused by residual oxygen. Furthermore, we propose a diffusion model for the formation of the iron oxide layer as the driving force for the reduction of interstitial excess iron that suppresses superconductivity in this compound. Overall, our results show that the presence of an iron reactant, such as oxygen, during annealing is necessary to improve the superconducting properties of FeSe1−xTex. [ABSTRACT FROM AUTHOR]

Nuclear relaxation is an important thermodynamic probe of electronic excitations, in particular in conducting and superconducting systems. Here, an empirical phenomenology based on all available literature data for planar Cu in hole-doped cuprates is developed. It is found that most of the seemingly different relaxation rates among the systems are due to a temperature-independent anisotropy that affects mostly measured 1/T1∥, the rate with an external magnetic field along the crystal c-axis, while 1/T1⊥ is largely independent on doping and material above the critical temperature of superconductivity (Tc). This includes very strongly overdoped systems that show Fermi liquid behavior and obey the Korringa law. Below Tc, the relaxation rates are similar, as well, if plotted against the reduced temperature T/Tc. Thus, planar Cu nuclear relaxation is governed by a simple, dominant mechanism that couples the nuclei with varying anisotropy to a rather ubiquitous bath of electronic excitations that appear Fermi liquid-like irrespective of doping and family. In particular, there is no significant enhancement of the relaxation due to electronic spin fluctuations, different from earlier conclusions. Only the La2−xSrxCuO4 family appears to be an outlier as additional relaxation is present; however, the anisotropy remains temperature independent. Also systems with very low doping levels, for which there is a lack of data, may behave differently. [ABSTRACT FROM AUTHOR]

We report the results from a study of europium-doped fluorochlorozirconate glasses that have been thermally processed to induce nucleation and crystallization of BaCl2 crystallites. The resulting glass ceramics show a photostimulated luminescence (PSL) effect with a conversion efficiency which is up to 80% of that found in the commercial crystalline x-ray storage phosphor material BaFBr:Eu2+. Thermal processing for 20 min in the range 240–260 °C produces small (∼6–11 nm) hexagonal BaCl2 crystallites, while temperatures in the range 270–290 °C lead to the formation and growth of larger (∼15–100 nm) orthorhombic BaCl2 crystallites, as well as additional unidentified phases. We observe only weak PSL from glass ceramics containing hexagonal BaCl2 (∼0.1% conversion efficiency compared to BaFBr:Eu2+ at room temperature), but orthorhombic phase crystallites give rise to a much larger relative efficiency that increases with particle size, and reaches ∼80% for 100 nm diameter particles. The PSL is attributed to the excitation of electrons trapped as F centers in the BaCl2 crystallites, while the dependence on crystallite size is consistent with a PSL-inert surface shell of thickness ∼7 nm surrounding the BaCl2 crystallites. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL), PL lifetime, and radioluminescence (RL) measurements were made on LaF3 nanoparticles doped with Eu3+ or Sm3+. The radiative lifetimes decreased with increasing rare earth concentrations, which can be attributed to energy transfer to the surface of the nanoparticles followed by non-radiative recombination. The RL signal increases with increasing concentration for Eu3+ concentrations up to 20% Eu3+ but it saturates and disappears for >10% Sm3+. A dose-independent RL was observed up to 10 kGy during continual X-ray irradiation for Eu3+ and Sm3+ doped nanoparticles, which is advantageous for real time dosimetry applications (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We report the dramatic effect of rationally-designed phosphopeptides on the size and shape of iron-iron oxide core-shell nanoparticles prepared in a one-pot synthesis by sodium borohydride reduction of an iron salt. These phosphopeptides are effective at small ratios of peptide to metal, in contrast to the behaviour of conventional capping agents, which must be added at high concentration to control the particle growth. Wet chemical techniques are attractive methods for the preparation of metal nanoparticles. Here, we report the dramatic effect of rationally-designed phosphopeptides on the size, shape and magnetic properties of iron-iron oxide core-shell nanoparticles prepared in a one-pot synthesis by sodium borohydride reduction of an iron salt. These phosphopeptides are effective at small ratios of peptide to metal, in contrast to the behaviour of conventional surfactants, which must be added at high concentration to control the particle growth. [ABSTRACT FROM AUTHOR]

A series of cerium-doped compounds with the composition Ba1-xLaxCl2+x and 0 < x < 0.5 have been prepared in ceramic form. We find from the powder X-ray diffraction patterns that the compounds adopt the cubic fluorite structure for 0.05 < x < 0.34. Samples with x ~ 0.2 are translucent. When doped with trivalent cerium, the materials show photoluminescence emission peaks at 350, 372 nm (for the Ba0.66La0.34Cl2.34 composition); the photoluminescence decay can be fitted with a single exponential with decay time 25 ns. The scintillation pulse height analysis shows a photopeak for 137Cs which can be used to compute a light yield of 4000 photons/MeV. The scintillation decay is non-exponential, with a rapid initial decay which can be represented approximately by a decay constant of ~100 ns, but there is a substantial delayed scintillation which extends over several microseconds. [ABSTRACT FROM AUTHOR]

We report the synthesis of Eu[SUP2+]- and chlorine-doped fluorozirconate glass-ceramics that show an intense photostimulated luminescence (PSL) after x-ray irradiation at room temperature. The PSL efficiency is up to 80% of that found in the well-known crystalline x-ray storage phosphor BaFBr:Eu[SUP2+], and it is the largest thus far reported for a glass-ceramic. We attribute the PSL to crystallites of orthorhombic BaCl[SUB2] that are formed after annealing above the glass temperature. Hexagonal BaCl[SUB2] crystallites are also observed after short annealing times, but they do not provide a measurable PSL signal. The photoluminescence peak from glass-ceramics containing orthorhombic BaCl[SUB2] crystallites occurs at 402 nm, and the stimulation band is centered at about 560 nm. [ABSTRACT FROM AUTHOR]