The room-temperature charge carrier mobility and excitation-emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite CsAgBiBr via a combinatorial approach; single crystal X-ray diffraction, optical excitation and temperature-dependent emission spectroscopy, resonant and nonresonant Raman scattering, further supported by first-principles calculations. We identify deep conduction band energy levels and that scattering from longitudinal optical phonons- via the Fröhlich interaction-dominates electron scattering at room temperature, manifesting within the nominally nonresonant Raman spectrum as multiphonon processes up to the fourth order. A Fröhlich coupling constant nearing 230 meV is inferred from a temperature-dependent emission line width analysis and is found to be extremely large compared to popular lead halide perovskites (between 40 and 60 meV), highlighting the fundamentally different nature of the two "single" and "double" perovskite materials branches.

The sensitive detection of X-rays embodies an important area of research, being motivated by a common desire to minimize the doses of ionising radiation required for detection. Amongst metal halide perovskites, the double perovskite Cs 2 AgBiBr 6 system has recently emerged as a highly promising candidate for the detection of X-rays, capable of high X-ray stability and sensitivity (105 µC.Gy −1 cm −2 ). Herein, we detail the important photophysical pathways in single crystal Cs 2 AgBiBr 6 at both room and liquid nitrogen temperatures, with emphasis made toward understanding the carrier dynamics which influence X-ray sensitivity. Our study draws upon a combination of optical probes and we develop a room temperature excitation model which is far from optimal, being plagued by a large trap density and fast recombination pathways above the conduction band minimum. We find that substantially improved operating conditions result at 77 K, due to a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. We characterise the temperature dependence of a single crystal Cs 2 AgBiBr 6 X-ray detecting device and reveal a strong and monotonic enhancement to the X-ray sensitivity upon cooling, moving from 316 µC.Gy −1 cm −2 at room temperature to 988 µC.Gy −1 cm −2 near liquid nitrogen temperatures. We conclude that even modest cooling -via thermoelectric Peltier device -will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.

Giant magnetocaloric effect has been observed in ErRu2Si2, which is associated with field-induced metamagnetic transition from antiferromagnetic to ferromagnetic state. The maximum values of magnetic entropy change (−ΔSMmax) and adiabatic temperature change (ΔTadmax) for a field change of 7T are evaluated to be 19.3J∕kgK and 15.9K, respectively, around 5.5K within the temperature range of 4–25K. The value of ΔTadmax is even larger than other potential magnetic refrigerant materials reported in the same temperature range and also comparable to room temperature giant magnetocaloric materials exhibiting first-order magnetic transition from paramagnetic to ferromagnetic state.

The reverse micelle sol-gel method was used earlier to prepare silica nanotubes, in aerosol OT/n-heptane/water microemulsions containing FeCl(3). The present communication reports the remarkable effect of the amount of water in the microemulsions on the shape, size, and spectral properties of the silica nanostructures formed. Nanotubes are formed, as expected, at lower water contents. However, for higher water contents, nanodisks form in predominance. This rather surprising observation indicates the formation of flat, disklike water pools in this medium. Notably, a phase separation occurs at higher water contents, and this appears to be essential for the formation of the disklike nanostructures. Hence, we propose that flat water pools form at the interface of the two liquid phases. The nanotubes and nanodisks exhibit blue photoluminescence. The photoluminescence of the nanotubes is more susceptible to quenching by moisture than that of the nanodisks. Luminescence is restored by heating or purging nitrogen or oxygen. Time-resolved photoluminescence studies conform to a model in which the luminescence is ascribed to a particular kind of defect center, with some contribution from surface-associated defects.

Giant magnetocaloric effect in antiferromagnetic borocarbide superconductor RNi2B2C (R=Dy, Ho, and Er) compounds J. Appl. Phys. 110, 043912 (2011); 10.1063/1.3625250The hydrogen absorption properties and magnetocaloric effect of La0.8Ce0.2(Fe1−xMnx)11.5Si1.5Hy

Polymer-surfactant mixtures are found in many industrial formulations, and hence there is a significant interest in understanding, at a molecular level, how the self-assembly of surfactant is affected by oppositely-charged polyelectrolytes (PEs). We use self-consistent field modeling and show that the modes of interaction of PEs strongly depend on the architecture of the PE on the segmental level. Hydrophilic cationic PEs with their charge proximal to the linear backbone are expected to bind electrostatically to the outsides of the coronas of the spherical micelles of anionic surfactants, such as sodium laureth sulphate (SLES). As a result, the surfactant aggregation number increases, but at the same time the colloidal stability deteriorates, due to bridging of the PEs between micelles. PEs with their charge somewhat displaced from the backbone by way of short hydrophobic spacers, are expected to be present inside a micelle at the core-corona boundary. In this case the aggregation number decreases, yet the colloidal stability is retained. Hence, SLES tends to remove hydrophilic PEs from an aqueous solution, whereas it solubilizes more hydrophobic ones. The binding isotherm shows that the uptake of PEs remains typically below charge compensation and in this case the spherical micelle topology remains the preferred state.

Nanocrystalline Pr0.65(Ca0.7Sr0.3)MnO3 show large magnetocaloric effect at their charge order transition temperature (TCO) as well as at the temperature at which the spontaneous destabilization of charge ordered state occurs (TM). In comparison to their polycrystalline bulk form, TM’s are substantially enhanced in the cases of nanocrystalline samples, whereas their TCO’s remain almost unchanged. Although there is no clear signature of charge order transition in the temperature dependence of magnetic susceptibility and resistivity for the sample with the lower particle size, a clear maxima due to charge order transition is visible in its temperature dependence of change in magnetic entropy.

Some recent experimental studies show the invisibility of antiferromagnetic transition in the cases of manganites when their particle size is reduced to nanometer scale. In complete contrast to these cases, we have observed the signature of antiferromagnetic transition in the magnetocaloric properties of nanocrystalline La 0.125 Ca 0.875 MnO 3 of average particle size 70 and 60 nm similar to its polycrystalline bulk form. The system exhibit inverse magnetocaloric effect in its polycrystalline and nanocrystalline form. An extra ferromagnetic phase is stabilized at low temperature for the sample with particle size ∼ 60 nm.