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Luminescence properties of yttrium gadolinium orthovanadate nanophosphors and efficient energy transfer from VO43- to Sm3+ via Gd-3+ ions
No full textIn this paper, luminescence properties of orthovanadates, Y1-x-yGdxVO4:ySm(3+) (where x = 0.05-0.50, y= 0.01-0.05), and the energy transfer mechanism from VO43- to Sm3+ via Gd3+ ions were investigated in detail. X-ray diffraction (XRD) analysis confirmed the crystalline phase for synthesized nanophosphor in a tetragonal structure with I41/amd space group. The average crystallite size estimated from XRD was similar to 28 nm. Field-emission scanning electron microscopy coupled with energy dispersive X-ray analysis revealed oval shaped morphology and composition of the nanophosphor, respectively. From high-resolution transmission electron microscopy observations, the particle sizes were found to be in the range 10-80 nm. The photoluminescence studies of Y0.77Gd0.20VO4:0.03Sm(3+) nanophosphor under 311 nm excitation exhibits dominant emission peak at 598 nm corresponding to (4)G(5/2) -> H-6(7/2) transition. The energy transfer occurs from VO43- to Sm3+ via Gd3+ ions was confirmed by applying Dexter and Reisfeld's theory and Inokuti-Hirayama model. Moreover, the energy transfer efficiencies and probabilities were calculated from the decay curves. Furthermore, Commission Internationale de l'Eclairage (CIE) color coordinate (0.59, 0.37) has been observed to be in the orange-red (598 nm) region for Y0.77Gd0.20VO4:0.03Sm(3+) nanophosphor. These results perfectly established the suitability of these nanophosphors in improving the efficiency of silicon solar cells, light emitting diodes, semiconductor photophysics, and nanodevices. (C) 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University
Metal-organic frameworks-derived titanium dioxide-carbon nanocomposite for supercapacitor applications
Get PDFThe pyrolysis of metal-organic frameworks (MOFs) to derive porous nanocarbons and metal oxides has attracted scientific attention due to the advantageous properties of the final products (eg, high surface areas). In the present research, MIL-125 (MIL = Materials of Institute Lavoisier, a Ti-based MOF) has been subjected to a single-step pyrolysis treatment in argon atmosphere. The combination of uniformly linked titanium metal cluster and oxygen-enriched organic linker has acted as a template to yield a titanium dioxide (TiO2)-carbon nanocomposite. The TiO2 nanoparticles infused in carbon skeleton structure (TiO2/C) has been investigated as an electrode material for supercapacitor applications. TiO2/C electrodes have delivered an excellent electrochemical performance, for example, in terms of charging-discharging efficiency. Two equally weighed TiO2/C electrodes have been used to assemble a solid-state symmetrical supercapacitor (SC) device, containing a gel electrolyte (poly vinyl alcohol in 1 M H2SO4). The above device has delivered a high value of energy density (43.5 Wh/kg) and an excellent power output of 0.865 kW/kg. The symmetrical SC could retain almost 95% of its initial capacitance even after 2000 charging-discharging cycles. The electrochemical performance of the TiO2/C SC was better than most MOF-based SCs reported previously. Such performance is attributed to the synergistic combination of electrically conducting MOF-derived carbon and redox active TiO2 nanocrystals with a large specific surface area
Microstructural and optical properties investigation of variable thickness of Tin Telluride thin films
No full textA series of Tin Telluride (SnTe) thin films of varied thicknesses are deposited on glass substrates at room temperature using thermal evaporation technique. The optical and microstructural properties of SnTe thin films of thicknesses 33 nm to 275 nm are reported. High-resolution x-ray diffraction patterns of SnTe thin films revealed the polycrystalline nature with [200] orientation having cubic structure. The microstructural and morphological structures of these films were examined using high-resolution transmission electron microscopy and scanning electron microscopy, respectively. The distribution of isotopes of various elements in the thin film along with lateral and longitudinal directions was determined by depth profile measurement using the time of flight - secondary ion mass spectroscopy technique. Fourier transform infrared spectroscopy spectra reveal the molecular vibrations, narrow bandgap property of material and suitability of materials in infrared applications. Longitudinal - optical phonon scattering due to the [222] orientation was observed in the micro-Raman spectra at room temperature which corresponds to a peak in the range 120-130 Raman shift/cm(-1). Hence, the change in optical and microstructural properties at the nano-regime resulted in a shift towards the near-infrared region with an increase in the thickness of the thin films
Microwave spin resonance investigation on the effect of the post-processing annealing of CoFe2O4 nanoparticles
Get PDFA novel investigation on the finite-size effects on the spin resonance properties of cobalt ferrite (CoFe2O4) nanoparticles has been performed using a room temperature ferromagnetic resonance (FMR) technique. A single broad spectrum was obtained for the CoFe2O4 nanoparticle samples, which indicated that all the samples were showing ferromagnetic characteristics. An asymmetric FMR line shape with a hefty trailing section was obtained due to the high magneto-crystalline anisotropy in CoFe2O4 nanoparticles, which changed with the size distribution. The resonance field for the samples shifted to a higher value due to the increase in the magneto-crystalline anisotropy in the CoFe2O4 nanoparticles with an increase in size. A systematic change in the resonance field and line width was observed with the change in the size distribution of the particles. Initially, it decreased with an increase in the size of the particles and increased after the critical size range. The critical size range is the imprint of the shift of the magnetic domain from a single domain to multi domain. The line width increased at higher annealing temperatures due to the enhancement in the dipole-dipole interaction, which led to a higher spin concentration as well as magneto-crystalline anisotropy. Furthermore, the saturation magnetization (M-s) as well as 'M-r/M-s' increased from 37.7 to 71.4 emu g(-1) and 0.06 to 0.31, respectively. The highest coercivity (750.9 Oe) and anisotropy constant (4.62 x 10(4) erg cm(-3)) were found for the sample annealed at 700 degrees C, which can be corroborated by the literature as the critical annealing temperature at which CoFe2O4 nanoparticles shift from single domain nanoparticles to multi-domain nanoparticles. Post-processing annealing is critical in advanced processing techniques and spin dynamics plays a vital role in various interdisciplinary areas of applications
Mn incorporated MoS2 nanoflowers: A high performance electrode material for symmetric supercapacitor
No full textEnergy storage devices based on the two-dimensional transition metal dichalcogenides (TMDs) have great interest due to their fascinating physical and chemical properties. In this study, Mn incorporated MoS2 nanosheets are self-assembled into nanoflowers via a simple one-step hydrothermal process. The nanoflowers retain the feature of the high specific surface area of the nanosheets and the intercalation of Mn atoms up to a certain amount increases the porosity of MoS2, thus enhancing active sites for reaction. The presence of an intermediate oxidation state of Mn (Mn3+), which also plays an important role in increasing capacitance, is highest in low doped sample resulting in superior capacitance performance compared to bare and high Mn content samples. So the supercapacitor electrode made of low Mn incorporated MoS2 nanoflowers exhibits maximum specific capacitance (430 F g(-1)), energy density 48.9 W h kg(-1) and power density 5.0 kW kg(-1) with excellent capacitance retention up to 5000 cycles at 10 A g(-1), when used as a supercapacitor electrode. Further, the performance of the electrode material has been examined by lightning four LED bulbs in series showing longer discharge time. Our findings open new areas to explore Mn doping with TMDs as next-generation energy devices systematically
Oxygen vacancies induced photoluminescence in SrZnO2 nanophosphors probed by theoretical and experimental analysis
Get PDFWe report, for the first time, the influence of oxygen vacancies on band structure and local electronic structure of SrZnO2 (SZO) nanophosphors by combined first principle calculations based on density functional theory and full multiple scattering theory, correlated with experimental results obtained from X-ray absorption and photoluminescence spectroscopies. The band structure analysis from density functional theory revealed the formation of new energy states in the forbidden gap due to introduction of oxygen vacancies in the system, thereby causing disruption in intrinsic symmetry and altering bond lengths in SZO system. These defect states are anticipated as origin of observed photoluminescence in SZO nanophosphors. The experimental X-ray absorption near edge structure (XANES) at Zn and Sr K-edges were successfully imitated by simulated XANES obtained after removing oxygen atoms around Zn and Sr cores, which affirmed the presence and signature of oxygen vacancies on near edge structure
Flexible CIGS, CdTe and a-Si:H based thin film solar cells: A review
No full textFlexible thin film solar cells such as CIGS, CdTe, and a-Si:H have received worldwide attention. Until now, Si solar cells dominate the photovoltaic market. Its production cost is a major concern since Si substrates account for the major cost. One way to reduce the module production cost is to use the low-cost flexible substrates. It reduces the installation and transportation charges also, thereby reducing the system price. Apart from metallic foils, plastic films and flexible glass, paper substrates such as cellulose papers, bank notes, security papers and plain white copying papers are also used as substrates for flexible solar cells. In this review, recent developments in flexible CIGS, CdTe and a-Si:H solar cells are reported. Progress on various flexible foils, fabrication and stability issues, current challenges and solutions to those challenges of using flexible foils, and industrial scenario are reviewed in detail. Encapsulation issues and solutions related to water vapor transmission rate are discussed
Fullerene (C-60)-modulated surface evolution in CH(3)NH(3)PbI(3)and its role in controlling the performance of inverted perovskite solar cells
Get PDFWe report here the effect of fullerene (C-60) incorporation on the growth of CH(3)NH(3)PbI(3)perovskite crystals and the effect on photovoltaic performance of perovskite solar cells (PSCs) prepared in inverse geometry. Incorporation of C(60)induced the growth of larger gains and compact thin film of perovskite with reduced defects, which led to its enhanced photovoltaic performance. Apart from that, C(60)also participates in transportation and collection of photo-generated electrons. The optimum incorporation of C(60)resulted in an impressive improvement in the power conversion efficiency (PCE) of champion PSC from 9.2 to 12.8%. Moreover, the C-60-doped PSCs exhibited improved air stability compared to undoped devices. The enhanced PCE in C-60-doped PSCs is a result of enhanced optical absorption and separation of photo-generated charge and their transportation in the active layer. Since the size of C(60)molecules is of the order of nm, they easily get filled into the perovskite voids and facilitate another percolation path ways for charge carriers to transport and suppress the recombination losses via passivating the recombination centres in perovskite layers. The compact perovskite layer with larger grains led to reduced inter-granular grain boundaries with reduced defects, which restricts the fast diffusion of moisture into active layer and resulted in improved stability in device performance
Growth and Characterization of MnBi2Te4 Magnetic Topological Insulator
Get PDFWe report successful growth of magnetic topological insulator (MTI) MnBi(2)Te(4)singlecrystalby solid state reaction route via self flux method. The phase formation of MnBi(2)Te(4)singlecrystalis strongly dependent on the heat treatment. MnBi(2)Te(4)is grown in various phases i. e., MnBi4Te7, MnBi6Te10 and MnTe as seen in powder X-ray diffraction (PXRD) of crushed resultant crystal. The Rietveld analysis shows some impurity lines along with the main phase MnBi2Te4. Low temperature (10K) magneto-resistance (MR) in applied magnetic field of up to 6 Tesla exhibited - ve MR below 0.5 Tesla and +ve for higher fields. The studied MnBi2Te4, MTI crystal could be a possible candidate for Quantum Anomalous Hall (QAH) effect. Here we are reporting a newly discovered magnetic topological insulator MnBi(2)Te(4)having non-trivial symmetry as well as strong Spin-Orbit Coupling forQAH effect
High-speed, low-bias operated, broadband (Vis-NIR) photodetector based on sputtered Cu2ZnSn(S, Se)(4) (CZTSSe) thin films
No full textPhotodetectors have large applications in the current ongoing pandemic. These can be used to study the growth of viruses where depending upon the concentration the light intensity will be reduced. Since the viruses grow very fast therefore a device with very low response time as well as quick recovery will be useful for this study. If the device can be made from the non-toxic materials and sizes are quite small, they can be used for in vitro studies as well. Kesterite Cu2ZnSn(5, Se)(4) (CZTSSe) thin film can be deposited over flexible substrates. The detectivity of even very small area device is very high with ultra-small response and recovery time. The CZTSSe PD exhibited excellent broadband (Vis-NIR) photoresponse, high responsivity of 18.0 mA.W-1, a fast rise time of 82 ms, and a decay time of 97 ms, as well as high detectivity (similar to 10(9) Jones) with favorable self-powered characteristics. This work suggests significant scientific insights for photoconductivity properties of emerging kesterite CZTSSe thin-film materials for broadband, low-cost, high-efficiency next-generation thin-film photodetectors for various optoelectronic applications including diagnostic