Achieving Deep Red Emission in Mn-Activated KMgGeO Phosphor with a Tetrahedral Network for Light-Emitting Diodes.

Designing a thermally robust Mn-based red-emitting phosphor is essential for warm phosphor-converted light-emitting diodes (pc-LEDs) with improved CRI and indoor plant cultivation applications. However, the major constraint is selecting a host with octahedral crystallographic sites and poor thermal stability. Herein, we report the stabilization of Mn ions in tetrahedral coordination in a KMgGeO matrix.

Broadband Shortwave Infrared-Emitting Cr- and Ni-Codoped YAlGaO Phosphor with Excellent Thermal Stability for Multifunctional Applications.

Shortwave infrared (SWIR)-emitting materials have emerged as superior light sources with increasing demand for potential applications in noninvasive analysis, night vision illumination, and medical diagnosis. For developing next-generation SWIR phosphor-converted light-emitting diodes (pc-LEDs), the scarcity of intense blue-light-pumped broadband SWIR luminescent materials and poor thermal stability of current Ni-activated phosphors are the ongoing challenges. Here, a blue-light-excitable (440 nm) YAlGaO:Cr,Ni phosphor with ultrawide SWIR emission centered at ∼1430 nm (FWHM ∼264 nm) is reported.

Development of magnetic La doped AlO core-shell nanoparticle loaded hydrogel for selective recovery of fluoride from aquatic medium.

The selective removal of pollutants from water bodies is regarded as a conciliation between the rapid expansion of industrial activities and need of clean water for sustainability. Fluoride is one such geogenic pollutant, and various materials have already been reported. Developing an efficient field employable material is however a challenge.

Local Structure and Speciation-Driven UO → Sm Energy Transfer for Enhanced Luminescence in LiBO.

Herein, we report the uranyl sensitization of Sm emissions in uranium-codoped LiBO:Sm phosphor. The uranyl speciation in codoped [Sm, U] LTB samples was determined by synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy that revealed two coordination shells for U(VI) ions with bond distances of U-O (∼1.81 Å) and U-O (∼2.

Probing site-selective doping and charge compensating defects in KMgF: insights from a hybrid DFT study.

Design of optoelectronic materials with tunable properties using activators and defect clusters has become one of the prime interests of current research. In this study, detailed Density Functional Theory based calculations have been presented to investigate the geometries and electronic structures of various possible defect clusters using Eu-KMgF as a probe which has numerous technological and industrial applications. Using a more reliable hybrid density functional, we have calculated defect formation energies and thermodynamic transition levels to get knowledge about the site selectivity of Eu.

Comprehensive study on the origin of orthorhombic phase stabilization in Gd-doped HfO and DFT calculations.

In recent times, ultra-thin films of hafnium oxide (HfO) have shown ferroelectricity (FE) attributed to the orthorhombic (o) phase of HfO with space group 2. This polar o-phase could be stabilized in the doped thin film of the oxide. In the present work, both polar and non-polar o-phases of HfO could be stabilized in Gd-doped bulk polycrystalline HfO.

Stabilization of Eu in LiBO with the BO network through U co-doping and defect engineering.

Owing to the unique 4f-5d transitions and the involvement of 5d electrons, the divalent europium (Eu) ion is extensively used as a dopant ion in luminescent materials for phosphor-converted light emitting diodes (pc-LEDs) and other technological applications. Earlier reports in most of the cases have shown that the reduction of Eu to Eu requires very high temperatures and large hydrogen flux. In this study, a co-doping strategy with higher valent U ions was utilized to successfully stabilize Eu ions in the LiBO (LTB) host with both the BO and BO network in low H flux of only 8%.

Design of need-based phosphors and scintillators by compositional modulation in the ZnGaAlO:Cr spinel: pure compound solid solutions.

Materials that can depict persistent deep red light under both ultraviolet (UV) and X-ray illumination can be a boon to sustainable economy, particularly for optical imaging, solid state lighting, and anticounterfeiting applications. Herein, we have made a series of compounds starting from ZnGaO:Cr to ZnAlO:Cr (individual spinel) by substituting the varied concentration of Al in place of Ga in ZnGaAlO:Cr (solid solution). By virtue of the structural and defect engineering doping strategy, the photo and radioluminescence are expected to be improved.

Unraveling the site-specific energy transfer driven tunable emission characteristics of Eu & Tb co-doped Ca(PO)F phosphors.

In this study we have explored Ca(PO)F as host to develop a variety of phosphor materials with tunable emission and lifetime characteristics based on Eu and Tb as co-dopant ions and the energy transfer process involved with them. The energy transfer from the excited state of Tb ion to the D state of Eu makes it possible to tune the colour characteristics from yellow to orange to red. Further, such energy transfer process is highly dependent on the concentration of Eu and Tb ions and their site-selective distribution among the two different Ca-sites (CaO and CaOF) available.

Harvesting Light from BaHfO/Eu through Ultraviolet, X-ray, and Heat Stimulation: An Optically Multifunctional Perovskite.

Materials with optical multifunctionality such as photoluminescence (PL), radioluminescence, and thermoluminescence (TL) are a boon for a sustainable society. BaHfO (barium hafnium oxide [BHO]) under UV irradiation demonstrated visible PL endowed by oxygen vacancies (OVs). Eu doping in BHO (BHOE) introduces f-state impurity levels just below the conduction band for both Eu@Ba and Eu@Hf sites, causing efficient host-to-dopant energy transfer, generating intense D → F magnetic dipole transitions (MDT) with internal quantum yield of ∼70%.

Unraveling U, Am&Eu ion's distribution in Ca(PO)Ffor radioactive waste immobilization and the associated U→ Euenergy transfer dynamics for tunable emission characteristics.

A combined photoluminescence (PL) and theoretical study has been performed on Ca(PO)F:U and Ca(PO)F:U,Eu compounds in order to explore Ca(PO)F as potential host for radioactive waste immobilization by understanding the distribution U, Eu and Am ions among the lattice sites and the related radiation stability. DFT based calculations on various structures with different distribution of U, Eu and Am ions showed that Eu and Am ions prefer to occupy the Ca2 sites while the highly charged U ions prefer Ca1 site. This is also supported by the PL lifetime study, which provided two lifetime components with different contribution for both U and Eu ions present at two different lattice sites.

Doping of MoS by "Cu" and "V": An Efficient Strategy for the Enhancement of Hydrogen Evolution Activity.

To replace Pt-based compounds in the electrocatalytic hydrogen evolution reaction (HER), MoS has already been established as an efficient catalyst. The electrocatalytic activity of MoS is further improved by tuning the morphology and the electronic structure through doping, which helps the band energy position to be modified. Presently, thin sheets of MoS (MoS-TSs) are synthesized via a microwave technique.

Multifunctional Ca(PO)F as a host for radioactive waste immobilization: Am/Eu ions distribution, phosphor characteristics and radiation induced changes.

NaEu:Ca(PO)F is explored as a potential host for radioactive waste immobilization. Since Eu ion is a surrogate of highly radioactive Am ion, the photoluminescence (PL) characteristics of Eu ion helped to investigate the possible distribution of hazardous and radioactive Am ion among the two lattice sites in the matrix. It was observed that Am will prefer to occupy the Ca2-site lattice which has a direct linkage to F atom.

Exploring the role of vacancy defects in the optical properties of LiMgPO.

Linearity in dose response up to very high radiation doses and sufficient sensitivity to even low radiation doses are extremely important for the measurement of radiation dose in the field of radiation technology, ranging from medical to industrial applications. Olivine type LiMgPO4 has been shown immense interest as a phosphor material in the fields of thermoluminescence and optically stimulated luminescence dosimetry. In the present study, we have explored the role of different vacancy defects in the optical properties of LiMgPO4 aiming at enhancing its sensitivity for the measurement of radiation dose.

Insight into the enhanced photocatalytic activity of SrTiO in the presence of a (Ni, V/Nb/Ta/Sb) pair.

Increasing applications of SrTiO3 as a photocatalyst in recent times drive the development of various strategies through doping with foreign elements to improve its efficiency under sunlight. Motivated by the recent experimental observation of increased lifetime of photogenerated charge carriers due to codoping of Ta into Ni-doped SrTiO3 (R. Niishiro et al.

Improving the photocatalytic activity of s-triazine based graphitic carbon nitride through metal decoration: an ab initio investigation.

Graphitic carbon nitride based semiconductor materials are found to be potential photocatalysts for generating hydrogen through solar water splitting. Through more accurate hybrid density functional theory calculations, we attempted to tune the electronic band structure of poly s-triazine based graphitic carbon nitride by decorating it with different metal atoms and clusters for improving its visible light absorption efficiency. For deposition on the two-dimensional carbon nitride surface, a range of metals have been considered which include all the 3d transition metals and the noble metals (Ag, Au, Pt and Pd).

Exploring the Role of La Codoping beyond Charge Compensation for Enhanced Hydrogen Evolution by Rh-SrTiO3.

In this theoretical study, we investigate recent observation of enhancement of hydrogen evolution efficiency of Rh-doped SrTiO3 due to codoping with La at the Sr lattice site. Using hybrid density functional theory, we have systematically studied the electronic structure of (Rh, La)-codoped SrTiO3 and compared with that of Rh-doped SrTiO3, La-doped SrTiO3, and undoped SrTiO3. The aim of the present study has been to explore the role of different factors toward the observed enhanced photoactivity of (Rh, La)-codoped SrTiO3.

Origin of enhanced visible light driven water splitting by (Rh, Sb)-SrTiO3.

A systematic calculation, using hybrid density functional theory, has been carried out to investigate the origin of the enhancement of photo-conversion efficiency of Rh-doped SrTiO3 with codoping of Sb. In the case of Rh-doped SrTiO3, partially unoccupied states are introduced above the valence band, thus lowering the hole oxidation at the valence band (VB) drastically, which explains the poor oxygen evolution activity of Rh-doped SrTiO3. We show that the partially occupied t2g subset of the Rh 4d orbital is completely filled in the presence of Sb due to the transfer of the extra electron to the Rh center.

A hybrid DFT based investigation of the photocatalytic activity of cation-anion codoped SrTiO3 for water splitting under visible light.

In this study, the effect of cation (Mo or W) and anion (N) codoping on the band structure of SrTiO3 is investigated to improve its photocatalytic activity for water splitting under sunlight. We consider both the non-compensated and compensated codoping strategies using different ratios of the cationic and anionic dopants. The present study employs hybrid density functional theory to describe the electronic structure of all the systems accurately.

Band gap engineering of NaTaO3 using density functional theory: a charge compensated codoping strategy.

In this theoretical study, we employ a codoping strategy to reduce the band gap of NaTaO3 aimed at improving the photocatalytic activity under visible light. The systematic study includes the effects of metal (W) and nonmetal (N) codoping on the electronic structure of NaTaO3 in comparison to the effect of individual dopants. The feasibility of the introduction of N into the NaTaO3 crystal structure is found to be enhanced in the presence of W, as indicated by the calculated formation energy.

Structure of colloidal solution in presence of mixed electrolytes: a solvent restricted primitive model study.

The structure of colloidal solution in presence of mixed electrolytes is studied using Monte Carlo simulation and density functional theory, based on a four-component model of the spherical double layer. In this model the ions and solvent molecules are treated as charged and neutral hard spheres, respectively, having equal diameter, and in addition the mixture of mono- and multivalent co-ions are also considered. The macroion is considered as a uniformly charged hard sphere surrounded by the electrolyte and the solvent.

Ultrafast twisting dynamics in the excited state of auramine.

Relaxation dynamics of the excited state of bis-[4-(dimethylamino)-phenyl] methaniminium chloride (Auramine) has been investigated using subpicosecond time-resolved absorption spectroscopic technique in both aprotic and alcoholic solvents. The locally excited (LE) state, formed following photoexcitation of Auramine using 400 nm light, undergoes intramolecular charge transfer (ICT) process, which is accompanied by the twisting of the dimethylanilino groups. Time evolution of the transient absorption-stimulated emission spectra as well as the wavelength dependence of the temporal dynamics investigated in each kind of solvents suggest that the relaxation process proceeds via the formation of at least two transient states (TS I and TS II), which are geometrical conformers and consecutively formed following the decay of the LE state.

Theory of reversible electron transfer reactions in a condensed phase.

We have derived an exact analytical expression for the average forward rate of a reversible electron transfer reaction, modeled through a reaction coordinate undergoing diffusive motion in arbitrary potential wells of the reactant and the product in presence of a localized sink of arbitrary location and strength. The dynamics of diffusive motion is described by employing two coupled generalized diffusion reaction (Smoluchowski) equations with coordinate dependent diffusivity and delta sink. The average forward electron transfer rate constant obtained here for the system, with equilibrium or nonequilibrium distributions as initial condition, is determined by the forward and backward rate constants calculated based on the transition state theory and the weighted average rate for the well dynamics.