Search

To get insight into the thermal management of twisted bilayer graphene based devices, the interpretation of temperature variation on twisting properties becomes crucial. In this aspect, we report the temperature dependent Raman scattering of twisted bilayer graphene (tBLG) on the Si substrate having SiO2 thickness 300 nm. The tBLG samples have been directly grown on the copper foil substrate using a home-built low pressure chemical vapor deposition (LPCVD) setup. The temperature dependent Raman scattering has been studied on two samples of tBLG named as tB1 and tB2. The twisting nature of bilayer graphene film has been analyzed using R, G, and 2D peak characteristics in Raman spectra. The Raman mapping with respect to different peak parameters of G and 2D peak (intensity, width, and position), intensity ratio (I2D/IG) has been employed to probe the uniformity of tBLG film. In tB1, the R peak has been found at 1395.82 cm−1 and not observed in sample tB2 at room temperature. The temperature dependence of G and 2D peak frequency in Raman spectra has been investigated in the temperature range from 80 to 450 K. In tB1 and tB2, the temperature coefficient of G peak has been found to be - (0.97 ± 0.34) × 10−2 cm−1/K, and - (1.08 ± 0.15) × 10−2 cm−1/K, respectively. Further, the extracted value of temperature coefficient of 2D peak in tB1, and tB2 are - (2.92 ± 0.80) × 10−2 cm−1/K, and - (3.01 ± 0.29) × 10−2 cm−1/K respectively. Additionally, the twist angle has been estimated as ∼23°-27° for T ≤ 300 K and 3°-8° for T > 300 K in tB1. In tB2, it has been found to be ∼13°-16° for the temperature range of 80–200 K and 5°-9° for 250–450 K. These findings shed light on the twisting behavior of bilayer graphene film and its anharmonic properties.

Polymer nanocomposites with vital reinforcements of conductive fillers have evinced as next-generation high-performance materials with multi-functional applications. Herein, we report the facile synthesis of thermally stable, highly electrically conducting polyaniline multi-walled carbon nanotubes (PANI/MWCNT) nanocomposites doped in two different protonic acids, i.e. hydrochloric acid (HCl) and sulphuric acid (H2SO4). The doping acids significantly affect the electric and dielectric properties of conducting polymer nanocomposites. The paper probes in the synergistic effects of MWCNTs and the effect of doping acid on the thermal stability, conductivity and dielectric properties of the nanocomposites based on PANI nanofibres. The structural, morphological, optical, thermal and electrical properties were evaluated through X-ray diffraction, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, thermogravimetric analysis and two-point probe technique. Ascribed to the high interfacial interaction between PANI and MWCNT, and considering the effect of doping acids, nanocomposites with high thermal stability, enhanced conductivity and high dielectric constant that can store large electrical charges have been synthesized by surfactant-assisted, in situ oxidative polymerization of aniline, in the presence of potassium persulfate as oxidant. The micellar structure of surfactant assists the dispersion of MWCNTs as well as the formation of PANI/MWCNT tubular structures. The effect of surfactant below and above critical micelle concentration was also studied. This complete study would affirm such a nanocomposite which procures excellent electrical and dielectric properties for microelectronic applications.

The accurate and precise quantification of the number of layers of MoS2 nanosheets is highly desirable to accomplish the advanced optoelectronic device applications, which is a real challenge in cutting edge science. In recent years, multitudinous efforts have been put forward, but no certain protocol is available to validate the number of layers. In this aspect, we present various spectroscopic probes such as optical, Raman, and photoluminescence (PL) to quantify the number of layers in mechanically exfoliated MoS2 nanosheets. The contrast analysis of optical and scanning electron microscope (SEM) images has been performed to identify the number of layers. The Raman spectra indicate that E12g are shifted toward low-frequency and A1g peak in high-frequency direction during the transition from monolayer to bulk MoS2. The intensity, line width, and peak frequency of both Raman modes have shown the notable difference with the thickness variation. Moreover, the PL spectra show two prominent peaks at 679 and 6...

Methylammonium lead bromide (CH3NH3PbBr3) colloidal quantum dots (QDs) exhibit strong green photoluminescence (PL) with high photoluminescence quantum yield (PLQY) making it valuable for various optoelectronic applications. Under the influence of polar gaseous molecules, hybrid halide perovskites show changes in its structural and electrical properties. We, for the first time, have investigated the influence of NH3 gas molecules on the optical properties of CH3NH3PbBr3 colloidal QDs. The investigations carried out under a controlled environment reveal that even the presence of 37 ppm of ammonia (NH3) gas molecules causes a significant reduction in the PL intensity of CH3NH3PbBr3 colloidal QDs. The reduction rate of PL intensity can be tuned with the concentration of NH3 gas molecules. We propose that the decrease in PL intensity is because of the formation of a non-luminescent NH4PbBr3 phase under the presence of NH3 gas molecules. Further, the non-luminescent NH4PbBr3 retransformed into luminescent CH3NH3PbBr3 on the introduction of methylamine (CH3NH2) gas molecules. This reversible alternation in PL properties enables us to demonstrate its application for (NH3) gas sensing. The advantage of using CH3NH3PbBr3 colloidal QDs for luminescence-based sensing is that its green emission is visible with the naked eye even under daylight, which is easy to detect.

Strontium tellurite, lead tellurite and bismuth niobium tellurite glasses containing 1 to 2 mol% of Eu3+ and Er3+ were prepared by melt-quenching and found to contain anti-glass inclusions (droplet phase) of size of several micrometers. Anti-glasses are disordered crystals that have long-range order of the cations such as Sr2+, Pb2+, Bi3+, Nb5+ and Te4+ but have a disordered arrangement of the anions (O2−), therefore these materials exhibit sharp peaks in the X-ray diffraction patterns due to the long range cationic order but the Raman spectra show broad bands due to the vibrational disorder. The glass matrix and anti-glass inclusions in the samples were characterized by synchrotron micro-X-ray Fluorescence (XRF), Raman and photoluminescence mapping studies. The XRF line analysis confirmed that the anti-glass and glass matrix phases have equal concentration of metal ions. The samples containing Eu3+ show intense red photoluminescence at an excitation wavelength of 375 nm, while Er3+ doped samples exhibit strong green emission by the up-conversion of infrared photons (980 nm). The spatially resolved XRF, Raman and photoluminescence spectroscopy found that the inclusions and the glass matrix have the same metal ion concentration, short-range order, Te O speciation and the light emission properties.

The excitonic behavior in two-dimensional (2D) heterostructures of transition metal dichalcogenide atomic layers has attracted much attention. Here, we report, for the first time, the ultrafast beh...

A novel strategy has been devised to develop a single excitable dual emissive luminescent pigment for the formulation of unclonable security ink. The new advanced security features of the ink have been demonstrated successfully and make it highly suitable for the printing of valuable products, such as currency, passports, pharmaceuticals, and so forth for protection against duplicity. The formulation of the single excitable dual emissive luminescent pigment is based on the unexplored combinatory concept of the fluorescence@phosphorescence phenomenon, which provides a new feature in the composite. It emits intense red color (611 nm) upon illumination with a 254 nm UV lamp excitation source and long persisting green color (532 nm) when the excitation source is switched off. To study the feasibility of the single excitable dual emissive luminescent security ink for commercial applications, the patterns printed using this ink were not only subjected to rigorous atmospheric conditions such as hot, cold and humid conditions for six months, but also examined after treatment with various bleaching agents (ethyl alcohol, ethyl acetate, xylene, acetone, soap solution and laundry detergent) to ensure their chemical stability. The security features printed using the single excitable dual emissive luminescent security ink were found to be very stable against all of these stringent conditions. Hence, the exceptional results obtained using the single excitable dual emissive luminescent security ink offer a new pathway to prevent counterfeiting by generating advanced security features.

Ultrafast transient absorption (TA) spectroscopy has been carried out to study the charge carrier dynamics of CdSe core and CdSe/V2O5 core/shell quantum dots (QDs). A significant redshift accompanied by broadening in the first excitonic peak was observed in the UV-Vis absorption spectra of the core/shell QDs as the shell thickness increases. This interesting observation is related to a quasi-type-II alignment characterized by the spatial separation of an electron into the core/shell and a hole into the core. The observed optical excitonic spectra have further been used to study the energetics of CdSe and charge separated states with the concept of Marcus theory and confirmed that electron transfer takes place in the Marcus inverted region (). Moreover, the growth kinetics of the CdSe core and CdSe/V2O5 core/shell QDs, studied with TA spectroscopy, exhibits slow electron cooling in core/shell QDs because of the de-coupling of the electronic wave functions with their hole counterpart. These exciting properties reveal a new paradigm shift from CdSe QDs to CdSe/V2O5 core/shell QDs for highly suitable applications in photovoltaics (PV) and optoelectronic devices.

The ever-growing bridge between stretchable electronic devices and wearable healthcare applications constitutes a significant challenge for discovery of novel materials for ultrasensitive wide-range healthcare monitoring. Herein, we propose a simplistic, amenable, cost-effective method for synthesis of a vertically aligned carbon nanotube (VACNT)/poly(dimethylsiloxane) (PDMS) thin-film composite structure for robust stretchable sensors with a full range of human motion and multimode mechanical stimuli detection functionalities. Notably, the sensor features the best reported response of carbon nanotube (CNT)-based sensors with extensive multiscale healthcare monitoring of subtle and vigorous ambulations ranging from 0.004 up to 30% strain deformations, coupled with an exceptionally high gauge factor of 6436.8 (at 30% strain), super-fast response time of 12 ms, recovery time of 19 ms, ultrasensitive loading sensing, and an excellent reproducibility over 10 000 cycles. The sensor evinces distinctive electromechanical performances and reliability in real time for motions like wrist pulsing, frowning, gulping, balloon inflation, finger bending, wrist bending, bending, twisting, gentle tapping, and rolling. Therefore, the VACNT/PDMS thin-film sensor reveals the ability to be a propitious candidate for e-skin and advanced wearable electronics.

In the present scenario, conducting and lightweight flexible polymer nanocomposites rival metallic and inorganic semiconducting materials as highly sensitive piezoresistive force sensors. Herein, we explore the feasibility of vertically aligned carbon nanotube (VACNT) nanocomposites impregnated in different polymer matrixes, envisioned as highly efficient piezoresistors in sensor applications. Polymer nanocomposites are selectively designed and fabricated using three different polymer matrixes, i.e., polydimethylsiloxane (PDMS), polyurethane (PU), and epoxy resins with ideal reinforcement of VACNTs to enhance the thermal stability, conductivity, compressibility, piezoresistivity, and sensitivity of these nanocomposites. To predict the best piezoresistive force sensor, we evaluated the structural, optical, thermal, electrical, mechanical, and piezoresistive properties of the nanocomposites using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), I-V measurements, compressive stress-strain measurements, hysteresis, sensitivity, and force studies. The results demonstrate that the PDMS/VACNT nanocomposite is capable of sustaining large force with almost complete recovery and enhanced sensitivity, thereby fulfilling the desirable need for a highly efficient conductive and flexible force sensor as compared to PU/VACNT and epoxy/VACNT nanocomposites.

Herein, a novel strategy to design of unclonable triluminescent pigment derived security ink is formulated to protect valuable merchandise, bank notes, pharmaceuticals, confidential documents etc. against counterfeiting, by embedding luminescent security codes/images. This triluminescent security ink is designed with combinatory chemistry that involves the strategically admixing of the triluminescent functional composite pigments in commercially available polyvinyl chloride gold medium. The triluminescent functional composite pigment is composed of NaYF4: Yb3+, Er3+(Sodium Yttrium Fluoride doped with Ytterbium and Erbium ions), NaYF4: Eu3+ (Sodium Yttrium Fluoride doped with Europium ion) and ZnO (Zinc Oxide) materials which have multifunctional features as it looks white in ambient light and shows strong green (NaYF4: Yb3+, Er3+), red (NaYF4: Eu3+) and green (ZnO) colors at three different excitations of 980 nm, 254 nm and 379 nm wavelengths, respectively. The structural/microstructural and photoluminescence properties of triluminescent functional composite are confirmed by XRD (X-ray diffraction), SEM (Scanning electron microscope), TEM (Transmission electron microscope) and photoluminescence spectroscopic techniques, respectively. The quality and spatially distributed PL intensity of printed images/code from triluminescent ink was investigated by photoluminescence confocal mapping microscopy technique. Hence, the obtained results suggest that the security code/images printed by using ink formulated from triluminescent functional composite pigment provides one step ahead novel security features which could be easy to detect but extremely difficult to replicate.

The development of high volumetric or areal capacitance energy storage devices is critical for the future electronic devices. Hence, the hunting for next-generation electrode materials and their design is of current interest. The recent work in the two-dimensional metal hydroxide nanomaterials demonstrates its ability as a promising candidate for supercapacitor due to its unique structure and additional redox sites. This study reports a design of freestanding high-mass-loaded copper-cobalt hydroxide interconnected nanosheets for high-volumetric/areal-performance electrode. The unique combination of hydroxide electrode with high mass loading (26 mg/cm2) exhibits high areal and volumetric capacitance of 20.86 F/cm2 (1032 F/cm3) at a current density of 10 mA/cm2. This attributes to the direct growth of hydroxides on porous foam and conductivity of copper, which benefits the electron transport. The asymmetric supercapacitor device exhibits a high energy density of 21.9 mWh/cm3, with superior capacitance retention of 96.55% over 3500 cycles.

The present study aims to demonstrate the application of sugarcane bagasse as an excellent field emitter. Field emission property of as-pyrolyzed sugarcane bagasse (p-SBg) before and after the plasma treatment has been investigated. It has been observed that electronic nature of p-SBg transformed from semiconducting to metallic after plasma treatment. Maximum current and turn-on field defined at 10 μA/cm2 was found to be 800 μA/cm2 and 2.2 V/μm for as-pyrolyzed sugarcane bagasse (p-SBg) and 25 μA/cm2 and 8.4 V/μm for H2-plasma treated p-SBg. These values are found to be better than the reported values for graphene and activated carbon. In this report, pyrolysis of bagasse has been carried in a thermal chemical vapor deposition (Th-CVD) system in inert argon atmosphere. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) have been used to study the structure of both pre and post plasma-treated p-SBg bagasse’s sample. HRTEM study reveals that carbonaceous structures such as 3D-nanographene oxide (3D-NGO), graphite nanodots (GNDs), carbon nanotubes (CNTs), and carbon onions are present in both pre-treated and plasma-treated p-SBg. Hence, we envision that the performed study will be a forwarding step to facilitate the application of p-SBg in display devices.

We report the exotic photoluminescence (PL) behaviour of 3D topological insulator Bi2Te3 single crystals grown by customized self-flux method and mechanically exfoliated few layers (18 plus minus 2 nm)/thin flakes obtained by standard scotch tape method from as grown Bi2Te3 crystals.The experimental PL studies on bulk single crystal and mechanically exfoliated few layers of Bi2Te3 evidenced a broad red emission in the visible region. These findings are in good agreement with our theoretical results obtained using the ab initio density functional theory framework., Main MS (17 Pages text including 4 Figs): Suppl. info. (4 pages); Accepted Scientific Reports

Herein, we demonstrate the synthesis of dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor by a facile high-temperature solid-state method as a spectral convertor for the enhancement of conversion efficiency of solar cell. The dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor has cubic crystal structure with space group Ia 3 . The surface morphology of dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor has been investigated by scanning electron microscopy. The spectroscopic features of dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor have been examined by photoluminescence (PL) and time-resolved photoluminescence (TRPL). The dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor gives strong red emissions at 611 nm and 663 upon excitation wavelengths of 200–500 nm and 980 nm, respectively. The dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor has average lifetime ~ 598.7 µs. Further, PL intensity distribution in dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor have been examined by PL confocal microscopy. The spatially resolved PL mapping results reveal that dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor has PL emission throughout the sample at excitation wavelengths of 375 nm and 980 nm, respectively. Hence, the obtained results suggest that dual-mode Gd2O3:Eu3+, Er3+, Yb3+ phosphor could be a promising luminescent material for spectral convertor to improve the efficiency of next generation silicon solar cell.

Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm−1 at 10 μA cm−2), a low threshold field (0.41 V μm−1 at 100 μA cm−2) and a high field emission current density (7.71 mA cm−2 at 0.78 V μm−1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources.

A bright novel red emission was obtained from Eu3+: CaLa2ZnO5 (CLZO) Phosphors under visible excitation. We have successfully synthesized Eu3+: CLZO Phosphors by the solid state reaction method. The phase formation and surface morphological studies were analyzed by X-ray diffraction and Field emission scanning electron microscopy respectively. Thermal analysis was done by TG/DTA. Photoluminescence spectral profiles reveal that the strong red emission has been noticed at 626 nm (5D0→7F2) from the Eu3+: CLZO Phosphors under the excitation of 467 nm. The emission and excitation spectral profiles were systematically analyzed and their bands were assigned with corresponding electronic transitions. Upon increasing the Eu3+ concentration, the photoluminescence performance has also been increased remarkably. The optimized concentration of the Eu3+ was noticed at 14 mol%. Upon co-doping with Dy3+ ions to Eu3+: CLZO Phosphors, the red emission pertaining to Eu3+ was appreciably enhanced through energy transfer form Dy3+ to Eu3+ ions. The energy transfer mechanism was substantiated by several fluorescent methods. The prominent red emission of the Dy3+/Eu3+: CLZO Phosphors under blue excitation which suggests that these phosphor materials could be promising candidates for red luminescent optical devices.

A prominent sensitization effect of In 3+ ions is observed in In 3+ +Eu 3+ : PVA polymer composites under UV excitation. Consequently, it enhances the red emission performance of Eu 3+ ions in PVA system. We have successfully synthesized Eu 3+ : PVA, In 3+ : PVA and In 3+ +Eu 3+ : PVA polymer films by traditional solution casting method. The structural and ion-polymer interaction studies have been analyzed from XRD and FTIR spectral profiles. Eu 3+ doped PVA polymer composites are exhibited a red emission at 619 nm ( 5 D 0 → 7 F 2 ) under 396 nm ( 7 F 0 → 5 L 6 ) of excitation. Upon co-doping with In 3+ ions in different concentrations to the Eu 3+ : PVA polymer film, it exhibits predominant red emission than singly doped Eu 3+ : PVA under 396 nm of excitation due to energy migration from In 3+ to Eu 3+ . Successful emission photons of In 3+ ions are collectively absorbed by the Eu 3+ ions which lead the improvement of red emission. Optimized sensitization concentration of the In 3+ ions has been found to be 0.01 wt%. Possible energy migration phenomenon is elucidated by several fluorescent dynamics. The energy transfer process is substantiated by lifetime decay analysis and overlapped spectral studies. The Commission International de I-Eclairage chromaticity coordinates were calculated. The quantum efficiencies of the Eu 3+ ions and In 3+ ions in singly doped and co-doped polymer systems have been evaluated. From these results, these co-doped In 3+ +Eu 3+ : PVA composite polymer films might be proposed as encouraging candidates for bright red fluorescent materials for several photonic applications.

Transition metal oxides and sulfides have great potential for energy storage devices due to their large theoretical energy storage capacities. A facile technique was used for the synthesis of nanostructured and phase pure cobalt oxide (Co 3 O 4 ) and subsequently converting it to cobalt sulfide (Co 9 S 8 ). The effect of sulfurization on energy storage capacity of the cobalt oxide was explored. Microstructural characterizations using X-ray diffraction and scanning electron microscopic reveal formation of phase pure and nanostructured Co 3 O 4 and Co 9 S 8 . It was observed that the areal capacitance of Co 3 O 4 (983 mF/cm 2 ) improved significantly after converting to Co 9 S 8 (7358 mF/cm 2 ). The CV curves of the Co 9 S 8 electrode on bending showed outstanding stability with no change in energy storage properties. New insights into the better performance of Co 9 S 8 over Co 3 O 4 based on electrochemical investigations are presented. The performance of the Co 9 S 8 as an electrode material for energy storage applications was further investigated by fabricating a supercapacitor device. The supercapacitor device showed outstanding stability up to 5000 cycles of charge-discharge study. The performance of the supercapacitor was observed to be improving with temperature. The supercapacitor displayed ~100% enhancement in energy storage property on increasing temperature from 10 to 70 °C. Our results suggest that hydrothermally grown Co 9 S 8 on nickel foam can be utilized for high capacity, flexible and binder free electrode for energy storage applications.

Lanthanide coordination polymers (LnCPs), [Eu(HL)3(CH3OH)2]n (1) and [Tb(HL)3(CH3OH)(H2O)]n·H2O (2) (H2L = 3-(picolinamido)benzoic acid)), have been synthesized and characterized. Single crystal analyses of both LnCPs display that HL ligands not only coordinate to Ln ions but also act as the bridge between them generating one-dimensional (1D) chains. Such 1D chains further pack into three-dimensional (3D) architectures by the mediation of H-bonding interactions. Both LnCPs offer strategically placed exposed Lewis basic sites, which potentially interact with the electron-deficient nitroaromatics, whereas H-bonded 3D architecture having hydrophobic channels allows their facile inclusion within the network. A notable feature is the size-dependent sensing of nitroaromatics potentially governed by the packing of 1D chains into a 3D architecture. Both LnCPs act as the fluorescent sensor for quick, sensitive, and selective detection of nitrobenzene not only in solution but also in the vapor phase suggesting pote...

Herein, we demonstrate a strategy for facile synthesis of pristine MgO nanostructures at different pH values ranging from 7.9, 8.3 and 12.5 to explore their photoluminescence studies. These pH-dependent MgO nanostructures were characterized by various standard techniques such as XRD, SEM, EDS, TEM and photoluminescence (PL) spectroscopy. The obtained PL results clearly demonstrate that the PL emission spectra strongly depend upon growth environment. These nanostructures show a broad PL emission in visible region ranging from 400 to 680 nm at excitation wavelength of 330 nm. Hence, this study provides a unique feature to tailor the PL property of pristine MgO nanostructures which could be potentially used in luminescence harvesting for various optical display devices and sensing applications.

The duplicity of important documents has emerged as a serious problem worldwide. Therefore, many efforts have been devoted to developing easy and fast anticounterfeiting techniques with multicolor emission. Herein, we report the synthesis of multicolor luminescent lanthanide-doped Y2O3 nanorods by hydrothermal method and their usability in designing of unclonable security codes for anticounterfeiting applications. The spectroscopic features of nanorods are probed by photoluminescence spectroscopy. The Y2O3:Eu3+, Y2O3:Tb3+, and Y2O3:Ce3+ nanorods emit hypersensitive red (at 611 nm), strong green (at 541 nm), and bright blue (at 438 nm) emissions at 254, 305, and 381 nm, respectively. The SEM and TEM/HRTEM results reveal that these nanorods have diameter and length in the range of 80–120 nm and ∼2–5 μm, respectively. The two-dimensional spatially resolved photoluminescence intensity distribution in nanorods is also investigated by using confocal photoluminescence microscopic technique. Further, highly lumin...

Nanofibers of cobalt manganese oxide (CoMn2O4) were grown using an electrospun technique. Structural and microstructural characterizations confirm the formation of phase pure CoMn2O4 with high porosity. The potential application of CoMn2O4 nanofibers as an electrode material for energy storage device was studied using cyclic voltammetry and galvanostatic charge-discharge measurements. A specific capacitance of 121 F/g was observed with enhanced cyclic stability. Furthermore, an energy storage device was fabricated by sandwiching two electrodes separated by an ion transporting layer. The device showed a specific capacitance of 241 mF/cm2 in 3 M NaOH electrolyte. The effect of temperature on the charge storage properties of the device was also investigated for high temperature applications. The device showed about 75% improvement in the charge storage capacity when the temperature was increased from 10 to 70 °C. This research suggests that nanofibers of CoMn2O4 could be used for fabrication of energy storage devices which could operate in a wide temperature range with improved efficiency.

The industrial application of water splitting for oxygen evolution requires low cost, high performance and stable electrocatalysts which can operate at low overpotential. Here, we develop a high performance and stable electrocatalyst for the oxygen evolution reaction (OER) using earth abundant materials. A binder free approach for the synthesis of flower-shaped cobalt oxide (Co3O4) composed of nanosheets showed high OER catalytic activity. The Co3O4 electrode requires a low overpotential of 356 mV to achieve a current density of 10 mA cm−2 with a low onset potential of 284 mV. The electrode showed outstanding flexibility and stability. The catalytic activity of the Co3O4 electrode was very stable up to the 2000th cycle of the polarization study. The high catalytic activity and structural stability arise due to efficient and fast charge transportation through the nanosheets of Co3O4 which are in direct contact with the conducting nickel of the electrode. The porous structure of Co3O4 allows easy access of the electrolyte and escape of generated oxygen without damaging the structure. Collectively, the flower-shaped nanostructured Co3O4 electrode can be used as a flexible and high performance electrode for the OER in an industrial setup.

Reduced graphene oxide (rGO) has recently emerged as a very promising family of exotic carbon material with augmented performance in electronic and optoelectronic devices. Herein, we report an efficient and novel inorganic electroluminescent device geometry, where a new phosphor composite, reduced graphene oxide wrapped ZnS:Cu,Al, acts as an active emitting layer and an exfoliated hexagonal boron nitride (h-BN) as a dielectric layer. The roles of rGO in the active layer as a conductive support and local electric field enhancing agent are attributed to its wrinkles being unraveled compared with other carbon exotic nano-forms such as carbon nanotubes, graphite, charcoal and activated carbon, which significantly improves the brightness of the device (∼50 cd m−2 for 0.50 wt% rGO/ZnS:Cu,Al at 10 kHz and 110 V with an external quantum efficiency of ∼6.3% ± 0.1% and current efficiency of ∼0.81 ± 0.09 cd A−1). This new and facile strategy to construct the luminescent devices could be a paradigm shift towards cost effective, highly stable in air (for several days) and energy efficient next generation display devices.

Rare-earth free and biocompatible two dimensional carbon based boron oxynitride (2D BCNO) nanophosphors were synthesized using facile auto-combustion of inexpensive compounds such as urea, boric acid and polyethylene glycol at ambient atmosphere and relatively low temperatures. The surface morphology and microstructure images indicate that the nanophosphor has 2D layered structures and analogous mixed hexagonal lattices of boron nitride (BN) and graphene (C). The nanophosphor exhibits a single, distinct and broad photoluminescence emission and this emission colour can be easily tuned from violet to deep red by varying the amount of boron/carbon content. The time-resolved and photoluminescence spectroscopic results indicate that B–O act as luminescence centers, which are responsible for the tunable luminescent properties while carbon impurities induce energy levels in the band gap of 2D BCNO nanophosphors. These tunable and biocompatible luminescent nanophosphors are used for in vitro high-contrast cellular imaging of HeLa cells derived from human cervical cancer cells as well as in vivo imaging in C57BL/6J mice. Hence, these novel multi-colour emitting nanophosphors provide a paradigm shift in rare-earth free biocompatible nanoprobes for next generation high-contrast in vitro and in vivo imaging applications.

Monodispersed polyvinylpyrrolidone (PVP) arrested ZnS quantum dots (QDs) having diameter in range ~2-5 nm are synthesized by a colloidal precipitation method using PVP as the stabilizing agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Fourier transform infrared (FT-IR) spectroscopy are probed to investigate the structural information. The optical properties are studied using diffuse UV-visible reflectance and photoluminescence (PL) spectroscopy techniques. TEM images as well as XRD reflection peak broadening indicate the nanometer size particles formation with cubic (sphalerite) phase within the polymer matrix. Optical absorbance studies reveal an excitonic peak at around ~310 nm dictates the effect of quantum confinement effect in the ZnS QDs. PL emission spectra for ZnS QDs in PVP exhibit four emission peaks at ~382 nm, ~414 nm, ~480 nm and ~527 nm are observed. These excitonic emissions from ZnS QDs are caused by the interstitial sulfur/Zn vacancies and surface states.

Pseudocapacitors with nickel/cobalt hydroxide-based electrodes show promises energy storage devices, because they are economical and safe, but cycle stability and high current rate capability have not been achieved. We shed light on how magnesium in double-layered hydroxides serves as a supercapacitor electrode in optimal environments. Here we show the high rate capability and long-term stability of layered magnesium–cobalt double hydroxide (L-MCH) electrodes, which is superior to existing electrodes. The pseudocapacitor made with Mg2+ and Co2+ double hydroxide as active materials, does not have an intricate fabrication process. The L-MCH pseudocapacitor has a specific capacitance comparable to most double hydroxide-based materials and capacity retention greater than 107% over 10,000 cycles, which is in line with commercial devices. Our proposed method also offers a much faster and reliable route for electrode fabrication, which could result in the development of a new generation of supercapacitors, batteries and hybrid devices.

Zinc oxide (ZnO) one-dimensional nanostructures are extensively used in ultra-violet (UV) detection. To improve the optical sensing capability of ZnO, various nickel oxide (NiO) based p-n junctions have been employed. ZnO/NiO heterojunction based sensing has been limited to UV detection and not been extended to the visible region. In the present work, p-NiO/n-ZnO composite nanowire (NW) heterojunction based UV-visible photodetector is fabricated. A porous anodic aluminum oxide template based electrochemical deposition method is adopted for well separated and vertically aligned growth of composite NWs. The photoresponse is studied in an out of plane contact configuration. The fabricated photodetector shows fast response under UV-visible light with a rise and decay time of tens of ms. The wide spectral photoresponse is analyzed in terms of conduction from defect states of ZnO and interfacial defects during p-n junction formation. Light interaction with heterojunction along the length of the composite NW results in enhanced visible photoresponse of the detector and is further supported by simulation.

High-quality graphene is highly enviable material due to its seminal role amongst several areas in modern technology including its role as nanocarrier for site selective drug grafting and delivery applications. Here, we report a facile, cost-effective and single-step method to produce high-quality graphene through customised electrochemical exfoliation of graphite anode in alkaline electrolyte medium. The quality of graphene sheets (GS) were investigated by Raman, TEM/HRTEM, AFM, and FTIR techniques. The high quality as well as excellent Π-Π stacking nature of the honeycomb lattice of graphene was confirmed by measuring the quenching capability through photo-luminescence spectroscopy using organic dyes. A plausible mechanism for the graphite exfoliation has been given where evolution of high density of oxygen molecules exerts large force on the graphitic layers leads to exfoliation and consequent synthesis of graphene. Furthermore, to explore the application of the graphene sheets so synthesized, we carried out studies which may make them as suitable carriers for drug delivery. For this, graphene sheets were functionalized with L-cysteine and attached with the drugs Amphotericin-B (AmB) and Tamoxifen citrate (TMX). The conjugation of drugs with L-cysteine functionalized graphene has been confirmed through FTIR and Raman spectroscopic techniques. The drug loading efficiency of FGS for AmB and TMX was 75.00% and 94.31%, respectively. The present formulation of drugs (AmB and TMX) conjugated with graphene is suitable for the targeted drug delivery as it will enhance the efficacy and reduce cytotoxicity associated with drug.

A strategy has been demonstrated to design a biluminescent security ink using Eu(TTA)3Phen (ETP) and fluorescein for protecting the currency and other essential documents, viz., passport, bank chec...

Growth characteristics of high Indium content InGaN/GaN heterostructure on a-plane ( 11 2 ¯ 0 ) sapphire substrate by plasma assisted molecular beam epitaxy have been investigated in detail. The structural analysis is carried out by high-resolution X-ray diffraction measurements. A reduction in the lattice constant by 0.15% confirms the highly crystalline nature of the grown GaN film. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with less hexagonally pitted GaN surface. This high quality MBE grown GaN on ( 11 2 ¯ 0 ) sapphire is utilized as a template to grow InGaN film with high indium composition (41%). The elemental distribution and thickness of the grown film is ascertained by Secondary Ion Mass Spectroscopy which demonstrates a sharp interface between the grown structure. The photoluminescence emission spectrum shows a sharp near band edge emission of GaN at 3.42 eV along with a broad band emission related to defects and near band edge emission of InGaN (1.9 ± 0.05 eV) at room temperature. This study provides a new insight into the structural quality of In-rich InGaN/GaN based heterostructures on a-plane sapphire, which could be useful to develop highly-efficient nitride solar cell devices.

Carbon nanotubes (CNTs) have great potential for a variety of applications out of which composite reinforcement is the most promising one. Silicon carbide (SiC) with its unique properties is expected to enable significant enhancements in the existing properties of CNTs to a far-ranging variety of applications and systems. In this report SiC–CNT composites through the novel route of d.c. arc discharge technique using silicon powder as a filler in a graphite anode have been prepared. Structural characterization of these composites was studied using X-ray diffraction, Raman spectroscopy and transmission electron microscopy techniques and further spectroscopic characteristics were investigated using a photoluminescence spectrometer. The XRD results confirm the formation of SiC along the 111 plane (35.6°, d spacing 0.25 nm), which agreed with the d spacing values calculated from the fringes of HRTEM images. Further, the shifting in the Raman peak of SiC confirms the successful synthesis of SiC–CNT composites.

Herein, we introduce a novel strategy for the synthesis of Eu3+ doped α-sodium gadolinium fluoride (α-NaGd0.88F4:Eu0.123+) based luminomagnetic nanophosphors using a hydrothermal route. The synthesized nanophosphor has exceptional luminescent and paramagnetic properties in a single host lattice, which is highly desirable for biomedical applications. This highly luminescent nanophosphor with an average particle size ∼5 ± 3 nm enables high-contrast fluorescent imaging with decreased light scattering. In vitro cellular uptake is shown by fluorescent microscopy that envisages the characteristic hypersensitive red emission of Eu3+ doped α-sodium gadolinium fluoride centered at 608 nm (5D0–7F2) upon 465 nm excitation wavelength. No apparent cytotoxicity is observed. Furthermore, time-resolved emission spectroscopy and SQUID magnetic measurements successfully demonstrate a photoluminescence decay time of microseconds and an enhanced paramagnetic behavior, which holds promise for the application of nanophosphors in biomedical studies. Hence, the obtained results strongly suggest that this nanophosphor could be potentially used as a bimodal nanoprobe for high-contrast in vitro bioimaging of HeLa cells and external magnetic field tracking applications of luminomagnetic nanophosphors using permanent magnet.

Herein, we demonstrated the synthesis of a hollow cylinder with a new architecture of up to several centimeters in diameter and several centimeters long and having ∼100 μm wall thickness. The hollow carbon cylinder was formed by radially aligned CNTs. These CNTs were grown on ferrocene derived Fe nanoparticles deposited throughout the inner wall of the quartz growth tube. This new ingenious carbon architecture was grown by a customized spray pyrolysis method. Furthermore, we also synthesized such carbon hollow cylinders using different precursor concentrations (ferrocene:benzene), different phases and microstructures to evaluate their EMI shielding effectiveness. The structural and microstructural characterizations of these hollow carbon cylinders comprising radially aligned CNTs were examined through various techniques, including XRD, Raman, FTIR, XPS, SEM, TEM, and HRTEM spectroscopy. Furthermore, the magnetic measurements (M–H) were performed for such structures to probe the magnetic properties of these carbon hollow cylinders for different concentrations. Furthermore, the EMI shielding through different concentrations of Fe bearing CNTs were explored in detail for tailoring the desired shielding effectiveness value for possible potential applications. Hence, our synthesis method provides a unique architecture for promising next generation building blocks in the form of carbon hollow cylinders made up of radially aligned CNTs over the conventional randomly oriented CNTs. This could be directly used to make it as a co-axial cover for electrical cables to protect them from EMI pollutants.

Herein, we design and develop a field emission device utilizing highly porous carbon nanocup (CNC) films. These three-dimensional (3D) low-aspect ratio CNC structures were fabricated by a combination of anodization and chemical vapor deposition techniques. The low turn-on fields of 2.30 V μm−1 were observed to draw an emission current density of 1 μA cm−2 and a maximum emission current density of ∼1.802 mA cm−2 drawn at an applied field of ∼4.20 V μm−1. The enhanced field emission behavior observed from the CNC films is attributed to an excellent field enhancement factor of 1645. The observed field emission properties of CNC arrays are attributed to a synergistic combination of high aspect ratio, nano-sized radius of curvature, highly organized distribution of the emitters over the whole area of specimen and lower screening effect of the CNC arrays. These observations shed light on the effect of the stacking carbon layers of CNC on their electronic properties and open up possibilities to integrate new morphologies of graphitic carbon in nanotechnology applications. Thus, the low turn on field, high emission current density and better emission current stability enable CNC based future field emission applications.

Hollow structures of NiAs-type cobalt sulfide have been synthesized by a facile hydrothermal method. These hollow structured cobalt sulfides exhibit excellent electrochemical properties for supercapacitor applications (867 F g−1) and respectable hydrogen evolution activity. The symmetrical supercapacitor device fabricated using cobalt sulfide nanostructures showed an areal capacitance of 260 mF cm−2 with good flexibility and high temperature stability. The specific capacitance of the supercapacitor is enhanced over 150%, when the temperature is increased from 10 to 70 °C.

A novel strategy was introduced to produce large-scale pristine MgO nanostructures as a feasible candidate for light harvesting applications. Herein, MgO nanostructures with a nanoflakes-/nanofibers-like morphology were synthesized by a co-precipitation route at different calcination temperatures ranging from 500 to 1100 °C and well characterized by several standard experimental techniques, such as XRD, FTIR, SEM, EDX, and TEM, to confirm the formation of MgO nanostructures. Undoped MgO nanostructures obtained at 1100 °C exhibited a strong photoluminescence (PL) emission spectrum at 668 nm (hypersensitive red) at 466 nm excitation wavelength. Moreover, these nanostructures also showed strong blue (477 nm) and red (668 nm) luminescence emissions simultaneously at an excitation wavelength of 317 nm. Further investigations probed by PL mapping demonstrated the homogeneous distribution of PL intensity throughout the MgO surfaces and time-resolved photoluminescence spectroscopy results of these nanostructures indicated a decay time of less than 10 ns. Thus, the facile synthesis of these luminescent undoped MgO nanostructures provides a potential platform to harvest white light generation (a combination of blue and red emissions) as well as their potential use in LED applications.

To explore the practical feasibility of exotic carbon, various types of geometries of CNT configurations have been investigated such as CNT film, vertically aligned nanotubes, 3D pillared graphene-CNT network etc. High-performance and applicability of CNT derived electrodes in electrochemical energy storage depend on the structural design and high aspect ratio geometry. Here, we have strategically designed electrode derived from a special type of 3D geometry known as carbon hollow cylinders (CHCs) made up of CNTs arranged in the radial direction. The exceptional geometry provides a high areal capacity of 513.92 C/cm2 at an applied current density of 16 mA/cm2. Also, high specific energy of 41.13 mWh/cm2 at the specific power of 5694.92 mW/cm2 originated from supercapacitors and battery response of the electrode material was attained, which idealized the fundamental of theory of composite type electrode material. Hence, proposed geometry sets a stepping stone for a paradigm shift in light-weight electrode which is not only binder-free but also designed with a special geometry that provides an exceptional higher areal capacity with stable network.

To attain the expected outcomes of any measurement, probing the quality of graphene is a prerequisite among the various graphene samples. Herein, we investigate the identification of the number of layers in mechanically exfoliated graphene using Raman spectroscopy. The intensity ratio (I2D/IG) and peak width of the 2D peak have been used to distinguish the number of layers. The 2D peak consists of a single Lorentzian fit having peak width 24 cm−1 in single layer graphene (SLG) and splits into four, six and five components for bilayer, trilayer, and five layers respectively. Further, the quality of graphene has been analyzed by I2D/IG, Raman mapping and the charge carrier mobility. In addition, the high quality of graphene has been encapsulated in terms of two phonon scattering processes and the variation in I2D/IG of SLG as a result of crossover from electron-electron to electron-hole scattering. The maximum mobility of SLG has been obtained ∼11,931 cm2V−1s−1 when the peak width and I2D/IG are 23.88 cm−1 and 5.36 respectively. Hence, the present study sets a platform to use Raman scattering as a probe for quantification of graphene layers and Raman mapping with spatial resolution provides the solution for specific area selection to fabricate the next generation graphene based quantum devices.

Designing of electrode with electrochemically rich structure, outstanding mechanical robustness and high electrical conductivity remains a challenge. We report a design of entangled Sr–Co Layered double hydroxides (LDHs) two-dimensional structure for such electrode. The hierarchical electrode with entangled nanosheet exhibit high specific capacitance of 1415 F g-1 at 5 A g-1 current density, excellent rate capability, high energy (12.28Whkg−1) and power density (567.788 W kg-1) and outstanding stability (80% capacity retention over 5000 cycles). The asymmetric device cell of Sr–Co LDH/ACC gives high energy density (27.78 Whkg-1) and power density (499.96Wkg-1) with cyclic performance of 1000 cycles with 95.24% capacitance retention. Further, we provide a detailed analysis of the various electrolyte environment experienced by the electrode and their effect on electrochemical properties. We pick out three different electrolytes; LiOH, NaOH, KOH and show that both selected electrolyte and metal combination for LDHs paves the way for outstanding electrochemical performance.

Increasing counterfeiting of important data, currency, stamp papers, branded products etc., has become a major security threat which could lead to serious damage to the global economy. Consequences of such damage are compelling for researchers to develop new high-end security features to address full-proof solutions. Herein, we report a dual mode flexible highly luminescent white security paper and nanotaggants composed of nanophosphors incorporated in polymer matrix to form a nanofiber-based mat for anti-counterfeiting applications. The dual mode nanofibers are fabricated by electrospinning technique by admixing the composite of NaYF4 :Eu3+ @NaYF4 :Yb3+ , Er3+ nanophosphors in the polyvinyl alcohol solution. This flexible polymer mat derived from nanofibers appears white in daylight, while emitting strong red (NaYF4 :Eu3+ ) and green (NaYF4 :Yb3+ , Er3+ ) colors at excitation wavelengths of 254 nm and 980 nm, respectively. These luminescent nanofibers can also be encrypted as a new class of nanotaggants to protect confidential documents. These obtained results suggest that highly luminescent dual mode polymeric nanofiber-based flexible white security paper and nanotaggants could offer next-generation high-end unique security features against counterfeiting.

Polymer nanocomposites (PNCs) have become an exciting field of current research and have attracted a huge interest among both academia and industry during the last few decades. However, the multifunctional single-nanocomposite film exhibiting the combination of desired structure and properties still remains a big challenge. Herein, we report a novel strategy to address these problems by using versatile polymer glycidyl methacrylate (GMA) as a bridging medium between the filler and the polymer matrix, resulting in high density of interfaces as well as strong interactions, which lead to generation of tunable thermal, mechanical, and electrical properties in the materials. The nanocomposites prepared by GMA bridging exhibit the remarkable combination of thermal (Td = 342.2 °C, Tg = 150.1 °C ), mechanical (E = 7.6 Gpa and H = 0.45 Gpa ) and electrical (σ = 3.15 × 10−5 S/cm) properties. Hence, the conjugation approaches related to GMA bridging facilitate a new paradigm for producing multifunctional polymer nanocomposites having a unique combination of multifunctional properties, which can be potentially used in next-generation polymer-based advanced functional devices.

A strategy is demonstrated to protect valuable items, such as currency, pharmaceuticals, important documents, etc. against counterfeiting, by marking them with luminescent security codes. These luminescent security codes were printed by employing luminescent ink formulated from a cost effective dual-mode luminescent composite pigment of Gd1.7Yb0.2Er0.1O3 and Zn0.98Mn0.02S phosphors using commercially available PVC Gold medium. In the composite, Gd1.7Yb0.2Er0.1O3 and Zn0.98Mn0.02S account for upconversion and downconversion processes, respectively. The synthesis procedure of the composite involves the admixing of Gd1.7Yb0.2Er0.1O3 nanorods and Zn0.98Mn0.02S phosphor, synthesised by hydrothermal and facile solid-state reaction methods, respectively. The structural, morphological, microstructural, and photoluminescent features of Gd1.7Yb0.2Er0.1O3 nanorods, Zn0.98Mn0.02S phosphor and composite were characterised by using XRD, SEM, TEM, and photoluminescence (PL) techniques, respectively. The distribution of PL intensity of the printed pattern was examined by using confocal PL mapping microscopy. The obtained results reveal that security codes printed using ink formulated from this bi-luminescent composite pigment provide dual-stage security against counterfeiting.

In search of affordable, flexible, lightweight, efficient and stable supercapacitors, metal oxides have been shown to provide high charge storage capacity but with poor cyclic stability due to structural damage occurring during the redox process. Here, we develop an efficient flexible supercapacitor obtained by carbonizing abundantly available and recyclable jute. The active material was synthesized from jute by a facile hydrothermal method and its electrochemical performance was further enhanced by chemical activation. Specific capacitance of 408 F/g at 1 mV/s using CV and 185 F/g at 500 mA/g using charge-discharge measurements with excellent flexibility (~100% retention in charge storage capacity on bending) were observed. The cyclic stability test confirmed no loss in the charge storage capacity of the electrode even after 5,000 charge-discharge measurements. In addition, a supercapacitor device fabricated using this carbonized jute showed promising specific capacitance of about 51 F/g, and improvement of over 60% in the charge storage capacity on increasing temperature from 5 to 75 °C. Based on these results, we propose that recycled jute should be considered for fabrication of high-performance flexible energy storage devices at extremely low cost.

A novel method for demonstration of photoluminescence intensity distribution in upconverting nanorod bundles using confocal microscopy is reported. Herein, a strategy for the synthesis of highly luminescent dual mode upconverting/downshift Y1.94O3:Ho3+0.02/Yb3+0.04 nanorod bundles by a facile hydrothermal route has been introduced. These luminescent nanorod bundles exhibit strong green emission at 549 nm upon excitations at 449 nm and 980 nm with quantum efficiencies of ~6.3% and ~1.1%, respectively. The TEM/HRTEM results confirm that these bundles are composed of several individual nanorods with diameter of ~100 nm and length in the range of 1–3 μm. Furthermore, two dimensional spatially resolved photoluminescence intensity distribution study has been carried out using confocal photoluminescence microscope throughout the nanorod bundles. This study provides a new direction for the potential use of such emerging dual mode nanorod bundles as photon sources for next generation flat panel optical display devices, bio-medical applications, luminescent security ink and enhanced energy harvesting in photovoltaic applications.

Counterfeiting is a major current concern throughout the world, and recent technological advances have made counterfeiting of sophisticated products easy. It is therefore essential to develop further means to combat counterfeiting, including the use of new luminescent materials for security inks. Here, we report the synthesis by a sol–gel technique of a highly luminescent YBO3:Eu3+ phosphor, which can be scaled up to 1 kg amounts in single batches. This phosphor is both structurally and chemically stable and has a particle size of 110 ± 10 nm. It emits strongly at a wavelength of 591 nm (orange–red) upon excitation at a wavelength of 245 nm and is also excitable by wavelengths in the 280–480 nm range. The structural and microstructural characteristics and the photoluminescence behavior of the phosphor were characterized by SEM, TEM/HRTEM, and fluorescent spectroscopy, respectively. The phosphor was used with a commercially available PVC gold medium to produce a luminescent security ink for printing security codes, and the results were investigated by photoluminescence mapping instruments. TheYBO3: Eu3+ phosphor-based security ink described here provides a low-cost material for use in printing security codes that are easy to detect but difficult to counterfeit.Counterfeiting is a major current concern throughout the world, and recent technological advances have made counterfeiting of sophisticated products easy. It is therefore essential to develop further means to combat counterfeiting, including the use of new luminescent materials for security inks. Here, we report the synthesis by a sol–gel technique of a highly luminescent YBO3:Eu3+ phosphor, which can be scaled up to 1 kg amounts in single batches. This phosphor is both structurally and chemically stable and has a particle size of 110 ± 10 nm. It emits strongly at a wavelength of 591 nm (orange–red) upon excitation at a wavelength of 245 nm and is also excitable by wavelengths in the 280–480 nm range. The structural and microstructural characteristics and the photoluminescence behavior of the phosphor were characterized by SEM, TEM/HRTEM, and fluorescent spectroscopy, respectively. The phosphor was used with a commercially available PVC gold medium to produce a luminescent security ink for printing securi...

Nanoparticles exhibiting both magnetic and luminescent properties are need of the hour for many biological applications. A single compound exhibiting this combination of properties is uncommon. Herein, we report a strategy to synthesize a bifunctional luminomagnetic Gd2−xEuxO3 (x = 0.05 to 0.5) nanorod, with a diameter of ~20 nm and length in ~0.6 μm, using hydrothermal method. Gd2O3:Eu3+ nanorods have been characterized by studying its structural, optical and magnetic properties. The advantage offered by photoluminescent imaging with Gd2O3:Eu3+ nanorods is that this ultrafine nanorod material exhibits hypersensitive intense red emission (610 nm) with good brightness (quantum yield more than 90%), which is an essential parameter for high-contrast bioimaging, especially for overcoming auto fluorescent background. The utility of luminomagnetic nanorods for biological applications in high-contrast cell imaging capability and cell toxicity to image two human breast cancer cell lines T47D and MDA-MB-231 are also evaluated. Additionally, to understand the significance of shape of the nanostructure, the photoluminescence and paramagnetic characteristic of Gd2O3:Eu3+ nanorods were compared with the spherical nanoparticles of Gd2O3:Eu3+.

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.