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Luminescence thermal quenching (TQ) is one of the most critical problems to be solved for further improvement of phosphors' applications in lighting and many other fields. Herein, a novel strategy is demonstrated to achieve outstanding anti‐TQ performance with a substantial enhancement of Eu3+ red emission at 613 nm from Sc2MO3O12:Tb3+,Eu3+ phosphor. Its anti‐TQ performance is endowed by dual energy transfer (ET) pathways and intensified by the negative thermal expansion (NTE) property of the Sc2MO3O12 host. Remarkably, the photoluminescence (PL) emission intensity of Eu3+ from Sc2MO3O12:20%Eu3+,2%Tb3+ phosphor at 648 K reaches 507.3% of the initial intensity taken at 298 K. The lifetime of Eu3+ emission at 613 nm elongates with increasing measurement temperature. The experimental data and density functional theory (DFT) calculations reveal that the host structure shrinkage via NTE leads to the thermally boosted Eu3+ red emission by intensifying the consecutive ET and confinement of the absorption light. The potential of this phosphor as a dual‐mode high temperature thermometer based on both emission lifetime and intensity ratio read‐out modes is realized. This work provides inspiration to combine multiple strategies to achieve broad and dramatic anti‐TQ phosphors with enhanced performance for various optical applications. [ABSTRACT FROM AUTHOR]

Graphene nanomaterials functionalized with oxygen groups [graphene oxide (GO) and reduced GO (rGO)] are either doped with element nitrogen or nitrogen-containing aromatic moieties followed by the investigation of electrochemical properties that generally show enhanced electroanalytical performance. We studied structural, morphological, and physical–chemical properties using correlative techniques. While we attribute their improved properties promoted simultaneously by topologically interconnected mesoporous network morphology, the presence of heteroatom species, and lattice vibrational structure, the complex interpretation requires the need to supplement the experimental observations with theoretical calculations for further insights. The complex interplay of pore size and redox properties revealing distinctive supercapacitive (ion-adsorption controlled) and pseudocapacitive (diffusion-controlled) energy storage mechanistic contributions arises from the combined effects of oxygen and nitrogen functional groups, most likely located on the basal plane and at the pore edge plane sites. The density functional theory calculations provided band structure and electron transfer from Mulliken and Hirshfeld population analyses helping discern the nature of various functional groups in diverse graphene. Interestingly, while quaternary (N—Q) and pyridinic-N-oxides (N—O) on the basal planes show enhanced capacitance due to positive charge and thus an improved electron transfer at higher current loads identified in nitrogen-doped aerogel (AG/nitrogenated) and GO-derived rGO by chemical and electrochemical properties, the other important functional groups affecting the energy storage are pyridinic (N-6) and pyrrolic (N-5) nitrogen groups on the edge of the rGO nanosheet in association with carboxylic (—COOH) and quinone (C=O) functional groups in nitrogenated functional graphene/graphene aerogel and rGO coated polyaniline, contributing to a pseudocapacitive character. [ABSTRACT FROM AUTHOR]

The electron density topology of carbon monoxide (CO) on dry and hydrated platinum is evaluated under the quantum theory of atoms in molecules (QTAIM) and by adsorbate orbital approaches. The impact of water co-adsorbate on the electronic, structural, and vibrational properties of CO on Pt are modelled by periodic density functional theory (DFT). At low CO coverage, increased hydration weakens C–O bonds and strengthens C–Pt bonds, as verified by changes in bond lengths and stretching frequencies. These results are consistent with QTAIM, the 5σ donation-2π* backdonation model, and our extended π-attraction σ-repulsion model (extended π-σ model). This work links changes in the non-zero eigenvalues of the electron density Hessian at QTAIM bond critical points to changes in the π and σ C–O bonds with systematic variation of CO/H2O co-adsorbate scenarios. QTAIM invariably shows bond strengths and lengths as being negatively correlated. For atop CO on hydrated Pt, QTAIM and phenomenological models are consistent with a direct correlation between C–O bond strength and CO coverage. However, DFT modelling in the absence of hydration shows that C–O bond lengths are not negatively correlated to their stretching frequencies, in contrast to the Badger rule: When QTAIM and phenomenological models do not agree, the use of the non-zero eigenvalues of the electron density Hessian as inputs to the phenomenological models, aligns them with QTAIM. The C–O and C–Pt bond strengths of bridge and three-fold bound CO on dry and hydrated platinum are also evaluated by QTAIM and adsorbate orbital analyses. [ABSTRACT FROM AUTHOR]

Electrochemical activity of graphene and graphene-based "hybrid" nanomaterials is crucial for energy and water sustainability applications, which requires fine tuning over combined geometric and electronic structures. We demonstrate that precise control of defects, porosity, and topological interconnectedness, invoked in hydrothermally synthesized graphene aerogel integrated with multi-walled carbon nanotubes, promotes finely tuned morphology, structure, defect number density, hierarchical mesoporosity, and conductivity and enhances the electrochemical heterogeneous electron transfer rate (kET). We prepared a range of graphene-based "hybrid" scaffolds (or monolithic aerogels) and their nitrogenated equivalents with varying graphene–carbon nanotube compositions using two synthetic schemes known as approaches 1 and 2. This study allows us to correlate quantitatively between number defect density (via Raman spectroscopy; RS) and heterogeneous electron transfer rate (via scanning electrochemical microscopy). RS provided microscale structural characterization revealing localized lattice vibrations. The first- and second-order Raman bands were analyzed in terms of band position, intensity ratio, and integrated intensity determining structural disorder, in-plane cluster size, inter-defect distance, and number defect density. The role of oxygenated (carbonyl; C═O, carboxyl; —COOH) and nitrogenated (pryridinic-N and graphitic/pyrrolic-N) functionalities and bonding configurations besides mesoporosity is emphasized for understanding the role of surface chemistry in regionally improved physicochemical (electroactivity and catalytic) properties. The defect-induced increase in finite electronic density of states (DOS) near Fermi level calculated using density functional theory under hydration helped in establishing moderate defect density for enhanced heterogeneous electron transfer rate as a critical onset such that the carbon system is electroactive while maintaining integral sp2 C structural network. Moreover, the defect sites allow sufficient overlap between DOS for graphene-based aerogels and redox probe wavefunctions, which emphasizes the experimental correlation establishments. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and x-ray absorption fine structure (XAFS) spectroscopy are complementary tools for the biophysical study of active sites in metalloproteins. DFT is used to compute XAFS multiple scattering Debye Waller factors, which are then employed in genetic algorithm-based fitting process to obtain a global fit to the XAFS in the space of fitting parameters. Zn-Cys sites, which serve important functions as transcriptional switches in Zn finger proteins and matrix metalloproteinases, previously have proven intractable by this method; here these limitations are removed. In this work we evaluate optimal DFT nonlocal functionals and basis sets for determining optimal geometries and vibrational densities of states of mixed ligation Zn(His)4-n(Cys)n sites. Theoretical results are compared to experimental XAFS measurements and Raman spectra from the literature and tabulated for use. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculated spectra was used to correlate the operando infrared (IR) spectroscopy, polarization modulated IR spectroscopy (PM-IRRAS) of Pt-Nafion interfaces, and attenuated total reflectance IR spectroscopy of bulk Nafion to understand the Nafion functional group coadsorption responsible for the Stark tuning of [CO.sub.ads] on high surface area fuel cell electrodes. A model of the Nafion-Pt interface with appropriate dihedral and native bond angles which was consistent with experimental and calculated spectra indicated direct adsorption of the C[F.sub.3] and S[O.sub.3.sup.-] functional groups on Pt.