[en] Upconverting (UC) nanoparticles have been an unmatchable part for the people of optical world in the past decade because of their stupendous luminescence properties, photostability, effective quantum efficiency and most of all for its voluminous power of converting infra-red (IR) waves into visible radiation. In this article, we have successfully reported the synthesis of novel Yb³⁺, Ho³⁺, Tm³⁺ doped lead tungstate nanophosphor by facile hydrothermal technique, where the product can also be scaled up to a large quantity. The phase purity and structure of the samples were characterized using X-Ray diffractometer and the morphology was studied using FEG TEM which shows formation of nanospheres of average particle diameter ranging between (25–45) nm. Photoluminescence studies of the nanophosphor were carried out using spectroflurophotometer which shows red, green and blue emissions due to the energy level transitions viz. ⁵F₅ → ⁵I₈ and ⁵S₂/⁵F₄ → ⁵I₈ of Ho³⁺,¹G₄ → ³H₆ of Tm³⁺ respectively. The pumping power variation data was recorded using variable power which implies that the UC mechanism is a mixture of two and three photon processes. The biexponential decay kinetics measurement was also done using the pulse mode laser source which shows the mean lifetime of 21.1 μs, 12.03 μs and 30.44 μs for blue, green and red emission respectively. Due to the perfect intermixing of the red, green and blue emissions in the optimum sample, a bright white light is obtained with CIE co-ordinate indexed as (0.34573,0.3449). The correlated colour temperature (CCT) value of the bright white light was calculated using McCamy’s approximations and it was found to be 4960 K which is almost equivalent to the colour “Horizon Daylight”. The colour temperature found after calculation, is eye-friendly and hence perfect for optoelectronics applications.

[en] Considering CuCrO₂ to be a promising p-type transparent conducting oxide, unprecedented simultaneous cationic–anionic doping is carried out to achieve superior hole transport while maintaining its transparency. Magnesium and sulphur are doped at Cr and O-sites respectively by solid-state approach (CuCr_1−xMg_xO_1−yS_y, x, y ranging 0–5 atomic %) with significant doping confirmed by Rietveld refinement. UV–Vis spectroscopy is observed to imply promising optical properties of engineered materials. DC conductivity of co-doped CuCr_0.95Mg_0.05O_1.9S_0.1 is observed to be twice as large compared to CuCr_0.95Mg_0.05O₂ at 300 K, which is consistent with the lower frequency shift of the negative differential susceptance ($-<!--\; ???\; -->\mathrm{\Delta <!--\; ??\; -->}B$) and the admittance peak, indicating higher ‘metallicity’ upon co-doping. Hole mobility of 16.26 cm² V⁻¹ s⁻¹ at 300 K is observed for the co-doped CuCrO₂. This strategy combines an established doping scheme at the cationic site with our newly developed anionic chalcogen doping, aiming to overcome a long-standing transport bottleneck in the field of semiconductor oxides. (paper)

[en] Highlights: • The spherically shaped ZnO NPs with uniform size (∼40 nm) were synthesized. • Optical and the UV detection properties of polymer composites were measured. • ZnO-PVP sample has the potential as a material for visible blind photo detector. • Dielectric medium perturbs electron-phonon interaction and UV detection mechanism. - Abstract: Spherical ZnO nanoparticles with average diameter ∼50 nm are synthesized by hydrothermal method. Composites of the nanoparticles with different polymers have been prepared and UV detection properties are measured. The dielectric medium perturbs electron-phonon interaction as well as the optoelectronic properties. Moreover, the luminescence properties of the materials effected due to composite formation. In case of NP-polymer composite NPs are capped and there is negligible further adsorption and desorption of O₂ molecules occurred on the surface. This increases the photocurrent as well as photosensitivity. For ZnO based photo detector, there is a small but not negligible photo response near 620 nm. The photo response in this particular wavelength is not observed in case of ZnO-PVP composite and it can be used as visible blind UV detector.

[en] For weak or moderate doping, electrical measurement is not suitable for detecting changes in the charge localization inside a semiconductor. Here, to investigate the nature of charge–phonon coupling in the presence of gradually delocalized holes within a weak doping regime (∼10¹⁶ cm⁻³), we examine the temperature dependent Raman spectra (303–817 K) of prototype hole doped delafossite $\mathrm{C}\mathrm{u}\mathrm{C}{\mathrm{r}}_{1-<!--\; ???\; -->x}\mathrm{M}{\mathrm{g}}_x{\mathrm{O}}_{2-<!--\; ???\; -->y}{\mathrm{S}}_y$ (x  =  0/0.03, y  =  0/0.01). For both $E_{\mathrm{g}}$ and $A_{1\mathrm{g}}$ phonons, negative lineshape asymmetry and relative thermal hardening are distinctly observed upon ${\mathrm{S}}_{\mathrm{O}}^{\times <!--\; ??\; -->}$ and $({\mathrm{M}\mathrm{g}}_{\mathrm{C}\mathrm{r}}^{\bullet <!--\; ???\; -->}+{\mathrm{S}}_{\mathrm{O}}^{\times <!--\; ??\; -->})$ doping. Using Allen formalism, charge density of states at the Fermi level per spin and molecule, and charge delocalization associated to $a-<!--\; ???\; -->b$ plane, are estimated to increase appreciably upon codoping compared to the $c$-axis. We delineate the interdependence between charge–phonon coupling constant ($\mathrm{\lambda <!--\; ??\; -->}$) and anharmonic phonon lifetime (${\mathrm{\tau <!--\; ??\; -->}}_{\mathrm{a}\mathrm{n}\mathrm{h}}$), and deduce that excitation of delocalized holes weakly coupled with phonons of larger ${\mathrm{\tau <!--\; ??\; -->}}_{\mathrm{a}\mathrm{n}\mathrm{h}}$ is the governing feature of observed Fano asymmetry ($q$) reversal. (paper)

[en] Tetragonal NaCe(WO${}_4$)${}_2$ with oxygen vacancy has been successfully synthesised by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal technique. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, etc. have been employed for detailed structural analysis, whilst oxygen vacancies, explored by Raman, FTIR and X-ray photoelectron spectroscopies, lead to distorted CeO${}_8$ dodecahedra (c.a. CeO${}_7$ and CeO${}_6$). It has been observed from photoluminescence spectra that the synthesised samples exhibit intense emission at 435 nm due to 5d-4f transition of Ce${}^{3+}$ within CeO${}_8$ dodecahedra, whilst emission at 485 nm is assigned for same transition within CeO${}_7$. CeO${}_6$ provides two emissions at 451 and 520 nm. Herein, we have identified that CTAB plays an important role in the formation of CeO${}_7$ and CeO${}_6$. In contrast to earlier ethylene-diamine-tetra-acetic acid-assisted NaCe(WO${}_4$)${}_2$ with predominant green emission, our samples exhibit strong violet emission indicating less formation of CeO${}_7$ and CeO${}_6$ by CTAB. Herein, our ab initio calculation using density functional theory reveals that valence and conduction bands comprise O 2p and O 2p-Ce 5d orbitals, respectively, whilst Ce 5d${}_z$${}^2$ and 5d${}_{yz}$, 5 d${}_{xz}$ orbitals mostly facilitate 5d-4f transition within CeO${}_7$ and CeO${}_6$. Commission Internationale de l'Elcairage coordinates are found in violet region with correlated colour temperature ∼ 6491 K indicating that CTAB-assisted hydrothermally synthesised NaCe(WO${}_4$)${}_2$ can be a potential material for cold solid-state lighting application.

[en] Amorphous carbon nanotubes were synthesized using low temperature solid state reaction. The as synthesized a-CNTs were used to remove two different textile dyes, Methyl Orange and Rhodamine B from water. Two ways of removal were followed; i.e. Adsorption and UV assisted catalysis. Adsorption experiment was carried out under various conditions. Analysis of the adsorption data was performed using Langmuir, Freundlich and Temkin models. It has been shown that the as prepared samples can effectively be used as adsorbent of textile dyes. Exposure of visible or UV light can make no significant additional effect to the removal efficiency.

abspara0015^>The mechanism of the adsorption has been found to be following a pseudo 1st order mechanism with corresponding correlation factor >0.95. Also it has been shown that presence of impurities can drastically kill the performance of the sample. This detail comparative study has been reported for the first time.

[en] Generation of white light requires a proficient strategy for appropriate mixing of red, green and blue emissions in appropriate proportion through optimization of material composition. However, it is quite challenging to develop a single host material showing emission in full visible region, which can be excited by a single excitation source. Herein, a series of Yb³⁺-sensitized Ho³⁺/Tm³⁺ co-doped BaWO₄ nanophosphors synthesized by hydrothermal method is reported. The effect of different concentration of sensitizer ion (Yb³⁺) on the luminescence properties of BaWO₄:Yb³⁺/Ho³⁺/Tm³⁺ crystal is investigated in detail to obtain white light. The phosphors exhibited red, green and blue luminescence centered at 651 nm, 539 nm and 482 nm respectively under a 980 nm excitation. The obtained novel nanophosphor could be a major potential candidate for nanobiotechnology and optoelectronics device applications.

[en] Solid-state white light emission from environment-friendly, highly stable hedgehog ZnO/Ag heterostructure has been observed for first time from a combined effect of tunability of emission centers and charge transfer. The heterostructure has been synthesized via a facile low-temperature hydrothermal route and characterized using X-ray diffractometer, scanning electron microscope and transmission electron microscope. The interaction between ZnO and Ag can be confirmed from the appearance of few new multi-phonon Raman peaks. Steady-state photoluminescence spectrum reveals multiple emissions (413, 453, 546, 605 and 667 nm) from virgin hedgehog ZnO at an excitation wavelength of 325 nm. Tuneability of radiative and non-radiative emission of ZnO which is the primary mechanism for white light emission (CIE coordinate: 0.35, 0.32) has been briefly investigated by time-correlated single-photon spectroscopy. Biocompatible as well cost-effectivity depicts that the as-prepared heterostructure would be a promising solid-state white light-emitting phosphor material for long-term use. Graphical abstract:

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[en] Upconverting nanophosphors are a special class of luminescent nanomaterials where lanthanide dopant assisted anti-stokes emission is exploited to achieve a wide range of applications. Herein we report Yb³⁺/Ho³⁺ co-doped BaWO₄ nanophosphor with a significant thermal and chemical stability synthesized by a low-temperature hydrothermal process with red (655 nm) and green (538 nm) double color upconversion (UC) under 980 nm near-infrared (NIR) excitation, resulting in yellow emission. The synthesized samples were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Vis–NIR Spectroscopy and Transmission Electron Microscopy (TEM) techniques. The dependence of emission behavior on various concentrations of activator ion (Ho³⁺) in BaWO₄: Yb³⁺:Ho³⁺ phosphors were studied in detail. Temperature dependent emission spectra revealed that the phosphor possesses stable emission up to 200 °C and luminescence intensity drop of only 11.5% of the initial luminescence intensity was observed at 150 °C. Therefore, the luminescence behavior and the thermal stability of the phosphor suggest an effective pathway in the optoelectronic applications.

[en] Highlights: • Synthesis of ZnPc nanotube via solvothermal method. • Synthesis of RGO/ZnPc nanocomposite. • Characterization of that prepared samples by XRD, UV-VIS, FESEM and RAMAN. • ORR performances of as synthesized materials. • Show methanol tolerance, possible electrocatalyst in DMFC. In recent years, sustainable energy resources in green environment are being extensively investigated. In pursuit of an efficient electrocatalyst for oxygen reduction reaction (ORR) in fuel cells, though pure platinum (Pt) is the unchallenged workhorse but high price, limited reserves and other factors has triggered the researcher to look for non Pt alternatives as catalysts. Metal based Phthalocyanine is one such prospective electrocatalyst for ORR in fuel cell. Herein, our work demonstrates the synthesis and ORR performances of Zinc Phthalocyanine (ZnPc) nanostructure and its composites with reduced graphene oxide (RGO). Electrochemical measurements show that the composite material exhibits better performances than pristine nanostructure in terms of limiting current density, onset potential, and half wave potential in alkaline medium. The improved electrochemical activity is attributed to the π–π interaction between ZnPc and RGO and also to the novel properties of graphene. The fascinating performances of ZnPc/graphene makes it a new viable electrocatalyst for different energy materials.