Analysis of Structural, Photoluminescence, and Colorimetric Performance of Gd-Incorporated BNT Ceramic.

Structural, optical, photoluminescence and colorimetric analyses of Gd (1-5 mol %) doped BNT ceramics synthesized by the solid-state reaction technique are reported. Structural analyses of all the samples are done by the X-ray diffraction method. It is shown that the samples have rhombohedral crystal structures with an R3C space group. The energy band gap of all the phosphors is computed from the UV-visible absorbance spectra. Photoluminescence behaviors are analyzed from the excitation along with the emission spectra of the prepared materials. The critical quenching concentration with the critical energy transfer distance is observed owing to the dipole-dipole interactions between the materials. Colorimetric analyses are carried out with the help of CIE chromaticity. Moreover, the color purity, correlated color temperature, color rendering index, and luminous efficiency of radiation values are evaluated by using the chromaticity coordinates.

New limits of secondary ß-relaxation.

Glass is an ultraviscous liquid that ceases to flow on a laboratory timescale but continues to relax on a geological timescale. Quintessentially, it has become hopeless for humans to explore the equilibrium behavior of glass, although the technology of glass making witness a remarkable advance. In this work, we propose a novel thermodynamic path to prepare a high density amorphous state of matter (carvedilol dihydrogen phosphate) using high pressure. In addition, we provide the impeccable experimental evidence of heterogeneous nature of secondary ß-relaxation and probe its properties to understand the various aspects of pressure densified glass, such as dynamics, packing and disorder. These features are expected to provide new horizons to glass preparation and functional response to pharmaceutical applications.

How Different Molecular Architectures Influence the Dynamics of H-Bonded Structures in Glass-Forming Monohydroxy Alcohols.

Primary alcohols have been an active area of research since the beginning of the 20th century. The main problem in studying monohydroxy alcohols is the molecular origin of the slower Debye relaxation, whereas the faster process, recognized as structural relaxation, remains much less investigated. This is because in many primary alcohols the structural process is strongly overlapped by the dominating Debye relaxation. Additionally, there is still no answer for many fundamental questions concerning the origin of the molecular characteristic properties of these materials. One of them is the role of molecular architecture in the formation of hydrogen-bonded structures and its potential connection to the relaxation dynamics of Debye and structural relaxation processes. In this article, we present the results of ambient and high-pressure dielectric studies of monohydroxy alcohols with similar chemical structures but different carbon chain lengths (2-ethyl-1-butanol and 2-ethyl-1-hexanol) and positions of the OH- group (2-methyl-2-hexanol and 2-methyl-3-hexanol). New data are compared with previously collected results for 5-methyl-2-hexanol. We note that differences in molecular architecture have a significant influence on the formation of hydrogen-bonded structures, which is reflected in the behavior of the Debye and structural relaxation processes. Intriguingly, studying the relaxation dynamics in monohydroxy alcohols at high pressures of up to p = 1700 MPa delivers a fundamental bridge to understand the potential connection between molecular conformation and its response to the characteristic properties of these materials.

Thermodynamic consequences of the kinetic nature of the glass transition.

In this paper, we consider the glass transition as a kinetic process and establish one universal equation for the pressure coefficient of the glass transition temperature, dTg/dp, which is a thermodynamic characteristic of this process. Our findings challenge the common previous expectations concerning key characteristics of the transformation from the liquid to the glassy state, because it suggests that without employing an additional condition, met in the glass transition, derivation of the two independent equations for dTg/dp is not possible. Hence, the relation among the thermodynamic coefficients, which could be equivalent to the well-known Prigogine-Defay ratio for the process under consideration, cannot be obtained. Besides, by comparing the predictions of our universal equation for dTg/dp and Ehrenfest equations, we find the aforementioned supplementary restriction, which must be met to use the Prigogine-Defay ratio for the glass transition.

Evidence of pressure induced intermolecular proton transfer via mutarotation: the case of supercooled d-fructose.

This paper describes a systematic investigation on the role of pressure in mutarotation kinetics of supercooled d-fructose using dielectric spectroscopy. The structural relaxation time acts as a suitable dynamical observable to monitor the mutarotation process that enables the construction of the kinetic curves. The reaction kinetic shapes have been analyzed using the Avrami model. At low temperature, sigmoidal kinetic curves are noted, which correspond to the high concentration of furanosidic forms. The magnitude of activation energy of the process significantly decreases with increasing pressure and is comparable to the solvated systems at 100 MPa. A potential connection between cooperative motion and the origin of intermolecular proton transfer via mutarotation at elevated pressure is also discussed. These experimental observations have fundamental significance on theoretical explanation of the mechanism involving mutarotation in sugars.

Glass transition dynamics and conductivity scaling in ionic deep eutectic solvents: The case of (acetamide + lithium nitrate/sodium thiocyanate) melts.

A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide + lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10(-1)-10(6) Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai's coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors.