Jet-cooled laser-induced fluorescence spectroscopy of B2Σ+–X2Σ+ system of scandium monoxide: Improved molecular constants at equilibrium

The investigation on B²Σ⁺–X²Σ⁺ system of ScO was extended to higher vibrational levels by laser-induced fluorescence (LIF) spectroscopy in a free-jet. We have observed rotationally resolved excitation spectra for (4,0), (3,0), (2,0), and (1,2) bands in addition to the previously observed (0,0) and (1,0) bands. The wavenumbers of these bands were fitted to a Hamiltonian matrix to determine the molecular constants for the vibrational levels up to ν′=4 of the B²Σ⁺ state and ν″=2 of the X²Σ⁺ state. In addition, the vibration constants of the ground states were determined from the dispersed fluorescence wavenumbers between B²Σ⁺ (ν′=0–4) and X²Σ⁺ (ν″=0–8) transitions. The equilibrium molecular constants, derived from the extensive set of molecular constants for individual vibrational levels, were used to construct RKR potential energy curves for both the electronic states. The Franck–Condon factors were also calculated for the B²Σ⁺–X²Σ⁺ transition.     

Morphology dependent luminescence properties of rare-earth doped lanthanum fluoride hierarchical microstructures

Here, we demonstrate an ionic liquid-assisted hydrothermal method for preparing Tb³⁺ and Eu³⁺ doped LaF₃ hierarchical microstructures and the morphology is modified by hydrothermal reaction time, temperature of heating and ionic liquid concentration. The mechanism related to morphology control is proposed and discussed. It is also found that PL intensity, decay time and quantum efficiency are sensitive to the morphology. The average decay times are 2.9 ms and 4.8 ms for Eu³⁺ doped LaF₃ microstructures prepared at 10 min and 3 h reaction time, respectively. The average decay time is increased from 4.8 ms to 5.8 ms after heating the sample at 500 °C. The quantum efficiency varies from 34% to 67% with changing morphology. Analysis suggests that morphology plays an important role on efficiency of rare-earth doped materials.     

Three-dimensional mid-infrared photonic circuits in chalcogenide glass

We report the fabrication of single-mode buried channel waveguides for the whole mid-IR transparency range of chalcogenide sulphide glasses (λ ≤ 11 μm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry that delivers a monochromatic interference visibility of 99.89% at 10.6 μm and an ultrahigh bandwidth (3-11 μm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing.     

Compact, highly efficient ytterbium doped bismuthate glass waveguide laser

Laser slope efficiencies close to the quantum defect limit and in excess of 78% have been obtained from an ultrafast laser inscribed buried channel waveguide fabricated in a ytterbium-doped bismuthate glass. The simultaneous achievement of low propagation losses and preservation of the fluorescence properties of ytterbium ions is the basis of the outstanding laser performance.     

Optical imaging of the growth kinetics and polar morphology of zinc tris(thiourea) sulphate single crystals

Growth kinetics of zinc tris(thiourea) sulphate (ZTS) single crystals was imaged in two different growth geometries using laser shadowgraphy technique. Growth rates of the {010} and {001} faces were computed as a function of supersaturation. The time evolution of polar morphology of ZTS crystal based on the growth rates is presented. Except (00 ) face, all the other three faces are found to have a dead zone resulting in large induction period of growth. The anisotropy in the growth rates of the (001) and (00 ) faces was very high, resulting in polar morphology. Different chemical environments on two sides of the (001) slice are suggested as the possible cause for the polar morphology of the crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of a Multilayer Perceptron Artificial Neural Network for the Prediction and Optimization of the Andrographolide Content in Andrographis paniculata

Andrographolide, the principal secondary metabolite of Andrographis paniculata, displays a wide spectrum of medicinal activities. The content of andrographolide varies significantly in the species collected from different geographical regions. Therefore, this study aims at investigating the role of different abiotic factors and selecting suitable sites for the cultivation of A. paniculata with high andrographolide content using a multilayer perceptron artificial neural network (MLP-ANN) approach. A total of 150 accessions of A. paniculata collected from different regions of Odisha and West Bengal in eastern India showed a variation in andrographolide content in the range of 0.28–5.45% on a dry weight basis. The MLP-ANN was trained using climatic factors and soil nutrients as the input layer and the andrographolide content as the output layer. The best topological ANN architecture, consisting of 14 input neurons, 12 hidden neurons, and 1 output neuron, could predict the andrographolide content with 90% accuracy. The developed ANN model showed good predictive performance with a correlation coefficient (R²) of 0.9716 and a root-mean-square error (RMSE) of 0.18. The global sensitivity analysis revealed nitrogen followed by phosphorus and potassium as the predominant input variables influencing the andrographolide content. The andrographolide content could be increased from 3.38% to 4.90% by optimizing these sensitive factors. The result showed that the ANN approach is reliable for the prediction of suitable sites for the optimum andrographolide yield in A. paniculata.     

Advances in transition metal dichalcogenide-based two-dimensional nanomaterials

Two-dimensional transition metal dichalcogenides (TMDCs) are the layered materials that have gained substantial consideration in a wide range of applications. The TMDCs possess exceptional properties such as high surface-to-volume ratio, excellent charge transfer capacity, mechanical strength, and low bandgap energy. Additionally, TMDCs (MoS₂, WS₂, etc.) are abundant, have a low synthesis cost, and are visible-light-active. The appealing surface morphologies and properties of TMDCs make them an appropriate choice for diverse applications like photocatalytic degradation of hazardous pollutants, energy conversion reactions (electrocatalytic and photocatalytic H₂ production), and energy storage devices (supercapacitors and rechargeable batteries) in addition to bio/chemical sensors. This article addresses the latest trends and advancements in the domain of TMDC-based nanomaterials. The different synthesis routes have been comprehensively reviewed. The challenges faced by TMDCs at a large scale and the future scope have also been discussed.     

Tunnelling Dynamics of Kicked Systems: A Route to Tunnelling Control

The effects of discontinuously time-varying perturbations on the dynamics of a particle moving in harmonic, symmetric double well and symmetric triple well potentials, are investigated both classically and quantum mechanically. The quantum dynamics is followed using the time-dependent Fourier grid Hamiltonian (TDFGH) method while the classical dynamics is analyzed within the framework of classical Hamiltonian mechanics. Depending on the spatial symmetry of the perturbation and the characteristic features of the reversal time , different types of ‘phase space’ structures are observed in each of the potentials. For symmetric double and triple well potentials, quantum dynamics reveals that complete destruction of tunnelling (CDT) can be achieved in the presence of a time-dependent spatially asymmetric perturbing field that is continuous in time. Any discontinuity in time-variation of the perturbation may induce over the barrier transition. The relevance of these results in the context of (i) tunnelling control and (ii) quantum computing with 3-state or 2-state quantum registers is briefly discussed.     

Harmonious Heterointerfaces Formed on 2D-Pt Nanodendrites by Facet-Respective Stepwise Metal Deposition for Enhanced Hydrogen Evolution Reaction

The performance of nanocrystal (NC) catalysts could be maximized by introducing rationally designed heterointerfaces formed by the facet- and spatio-specific modification with other materials of desired size and thickness. However, such heterointerfaces are limited in scope and synthetically challenging. Herein, we applied a wet chemistry method to tunably deposit Pd and Ni on the available surfaces of porous 2D−Pt nanodendrites (NDs). Using 2D silica nanoreactors to house the 2D-PtND, an 0.5-nm-thick epitaxial Pd or Ni layer ( e - Pd or e -Ni ) was exclusively formed on the flat {110} surface of 2D−Pt, while a non-epitaxial Pd or Ni layer ( n - Pd or n -Ni ) was typically deposited at the {111/100} edge in absence of nanoreactor. Notably, these differently located Pd/Pt and Ni/Pt heterointerfaces experienced distinct electronic effect to influence unequally in electrocatalytic synergy for hydrogen evolution reaction (HER). For instance, an enhanced H₂ generation on the Pt{110} facet with 2D-2D interfaced e -Pd deposition and faster water dissociation on the edge-located n -Ni overpowered their facet-located counterparts in respective HER catalysis. Therefore, a feasible assembling of the valuable heterointerfaces in the optimal 2D n -Ni/e-Pd/Pt catalyst overcame the sluggish alkaline HER kinetics, with a catalytic activity 7.9 times higher than that of commercial Pt/C.