Jaya Dwivedi

Highly luminescent dual mode rare-earth nanorod assisted multi-stage excitable security ink for anti-counterfeiting applications

In this paper, the synthesis of multi-stage excitable (379 nm, 980 nm and 1550 nm), highly luminescent Y2O3:Yb3+/Er3+ nanorods by a hydrothermal method which can emit both hypersensitive green (562 nm) and strong red (660 nm) in a single host lattice and which can be used for a transparent security ink application is reported. Furthermore, these luminescent nanorods also exhibit both down-shift (1127 nm) as well as upconversion (562 nm) features at a single excitation near infrared wavelength of 980 nm. The characterization of these luminescent nanorods was explored by studying their structure/microstructure, using photoluminescence and time-resolved spectroscopic techniques. Furthermore, these luminescent nanorods exhibited the tuning of emission colours from red to green by controlling the sintering temperature. It was demonstrated that these novel luminescent nanorods offer new opportunities for making high-end, multi-stage excitable transparent security ink. The state-of-art production process of ink is easy and it is most suitable for bulk production at an economical cost. Thus, the security inks could be used globally in applications for protection against counterfeiting.

A novel strategy to enhance ultraviolet light driven photocatalysis from graphene quantum dots infilled TiO2 nanotube arrays

Herein, a novel strategy has been proposed to fabricate graphene quantum dots (GQDs) infilled titanium dioxide (TiO2) nanotube arrays (NTAs) hybrid structure for dye degradation of methylene blue (MB) under UV light (365 nm) irradiation. GQDs are infilled inside the TiO2 NTAs (via anodic oxidation of a Ti sheet) through an impregnation method. Moreover, the morphology of the TiO2 NTAs is well maintained after filling the GQDs inside, which is favorable for mass transfer. The peak intensity of photoluminescence (PL) spectra of the GQDs infilled TiO2 NTAs catalyst is lower than that of annealed TiO2 NTAs and a strong violet UV emission is obtained at 387 nm upon 252 nm deep UV excitation. The photocatalytic activities of the TiO2 NTAs are evaluated in terms of the efficiencies of photo-decomposition and adsorption of MB in aqueous solution under UV light irradiation, after the impregnation of GQDs inside the TiO2 NTAs. The highly-efficient photocatalytic activity is attributed to the broad absorption in the visible wavelength region, large photo-induced charge separation through the transfer of photo-generated electrons from the TiO2 NTAs to GQDs, as well as the strong adsorption capacity of the GQDs to MB molecules. Thus, the GQDs infilled TiO2 NTAs could be widely used as a photocatalyst for treating organic contaminants in the field of environmental protection.

A commercial approach for the fabrication of bulk and nano phosphors converted into highly efficient white LEDs

Herein, we report a strategy to synthesize a highly efficient yellow light emitting Y3−xAl5O12:Cex (x = 0.03 to 0.3) based bulk as well as nano (rod-shaped) phosphors, which are the main component of solid state white light-emitting diodes (WLEDs). The as-synthesized phosphors were well characterized by several experimental techniques related to material characterization and spectroscopy. The bulk and nano phosphors emit with maximum photoluminescence intensities at 549 and 530 nm, respectively, upon excitation at a wavelength of 468 nm. These phosphors exhibit higher photoluminescence intensity as compared to commercially available bulk phosphors coated on WLED strips. Moreover, the integration of commercially available InGaN blue LED strips with the synthesized bulk and nano phosphors demonstrates better CIE coordinates and lower colour temperature with high brightness (>81% quantum yield) compared to commercially available WLED-based strips, lanterns and torches. These highly efficient light-emitting phosphors are a feasible candidate for potential use in commercial WLED applications.

Probing Highly Luminescent Europium-Doped Lanthanum Orthophosphate Nanorods for Strategic Applications

Herein we have established a strategy for the synthesis of highly luminescent and biocompatible europium-doped lanthanum orthophosphate (La0.85PO4Eu0.15(3+)) nanorods. The structure and morphogenesis of these nanorods have been probed by XRD, SEM, and TEM/HRTEM techniques. The XRD result confirms that the as-synthesized nanorods form in a monazite phase with a monoclinic crystal structure. Furthermore, the surface morphology shows that the synthesized nanorods have an average diameter of ∼90 nm and length of ∼2 μm. The HRTEM images show clear lattice fringes that support the presence of better crystal quality and enhanced photoluminescence hypersensitive red emission at 610 nm ((5)D0-(7)F2) upon 394 nm wavelength excitation. Furthermore, time-resolved spectroscopy and an MTT assay of these luminescent nanorods demonstrate a photoluminescent decay time of milliseconds with nontoxic behavior. Hence, these obtained results suggest that the as-synthesized luminescent nanorods could be potentially used in invisible security ink and high-contrast bioimaging applications.

High-Performance Stable Field Emission with Ultralow Turn on Voltage from rGO Conformal Coated TiO2 Nanotubes 3D Arrays

A facile method to produce conformal coated reduced graphene oxide (rGO) on vertically aligned titanium oxide (TiO2) nanotubes three dimensional (3D) arrays (NTAs) is demonstrated for enhanced field emission display applications. These engineered nano arrays exhibit efficient electron field emission properties such as high field emission current density (80 mA/cm2), low turn-on field (1.0 V/μm) and field enhancement factor (6000) with high emission current stability. Moreover, these enhancements observed in nano arrays attribute to the contribution of low work function with non-rectifying barriers, which allow an easy injection of electrons from the conduction band of TiO2 into the Fermi level of reduced graphene oxide under external electric field. The obtained results are extremely advantageous for its potential application in field emission devices.

Sunlight-activated Eu2+/Dy3+ doped SrAl2O4 water resistant phosphorescent layer for optical displays and defence applications

Herein, we introduce a strategy for the fabrication of a sunlight-activated green luminescent Eu2+/Dy3+ doped strontium aluminate (Sr1−x−yAl2O4:Eux2+/Dyy3+) assisted long persistent, transparent, flexible and water resistant phosphorescent layer via a customized solid state reaction-solution casting method. The XRD result of as-synthesized phosphor shows a pure monoclinic crystal structure with the space group P21. This as-synthesized phosphor exhibits green afterglow emission with a broad band peaking ∼528 nm upon a broad range of excitation wavelengths from 368–418 nm, which is ascribed to the characteristic 4f65d1 → 4f7 electronic dipole allowed transition of Eu2+ ions. Moreover, the role of Dy3+ as an auxiliary activator significantly prolongs the afterglow duration to a large extent by increasing the number of electron traps and their trap depths in the vicinity of Eu2+. Accordingly, a brighter afterglow intensity with a time more than 5 hours is observed for the optimal concentration of Eu2+/Dy3+ in Sr1−x−yAl2O4:Eux2+/Dyy3+, (x = 0.1 and y = 0.2) in the long persistent phosphor. The incorporation of the sunlight-activated as-synthesized Sr0.7Al2O4:Eu0.12+/Dy0.23+ phosphor in a commercially available PVC gold medium offers a highly dispersive transparent luminescent paint, which can be used for the spray coating of monuments, as well as for the fabrication of transparent, flexible and water resistant phosphorescent layers. Hence, these striking features of the luminescent paint, as well as the flexible transparent phosphorescent layer could be potentially utilized in optical displays and defence applications.

New emerging rare-earth free yellow emitting 2D BCNO nanophosphor for white light emitting diodes

We have demonstrated a new emerging rare-earth free highly-efficient two dimensional (2D) boron carbon oxynitride (BCNO) yellow emitting nanophosphor with high quantum efficiency for white light emitting diode (WLED) devices. This BCNO nanophosphor exhibits 2D layered structures analogous to hexagonal BN phase. Further, the EELS and XPS results confirm the nanophosphor consisted of B, C, N and O elements. The BCNO nanophosphor shows a broad highly intense yellow emission band centered at 580 nm corresponding to 470 nm excitation wavelength with a quantum efficiency approaching 89%. This novel nanophosphor with strong emission has subsequently been integrated to chip on board (CoB) based blue LEDs in order to fabricate WLEDs devices with a color rendering index of 92. Low color temperature (4899) and better CIE color coordinates (x = 0.3496, y = 0.3679) of a fabricated WLEDs device supports a 2D BCNO nanophosphor that could be an exceptional choice for CoB based WLEDs. Hence, our method provides a facile synthesis of rare-earth free 2D lightweight BCNO nanophosphor and its integration with CoB based blue LEDs for next generation advanced solid state white light applications.

Fabrication of a Flexible UV Band-Pass Filter Using Surface Plasmon Metal–Polymer Nanocomposite Films for Promising Laser Applications

We introduce a strategy for the fabrication of silver/polycarbonate (Ag/PC) nanocomposite flexible films of (20 ± 0.01) μm thickness with different filling factor of surface plasmon metal using customized solution cast-thermal evaporation method. Structural characterizations confirmed the good crystallinity with cubic phase of Ag nanoparticles in PC films. Moreover, the microstructural evolutions of nanocomposite films are investigated by transmission electron microscopy, which indicates that the metal fraction is in the form of fractals. Additionally, the surface plasmonic behavior of nanocomposite films has been explored in detail to examine the distribution of Ag nanoparticles in PC film by spectroscopic technique. Furthermore, the obtained transmittance spectral features of this nanocomposite film are suitable for the applications of band-pass filter at 320 nm UV range, which is highly desirable for a HeCd laser.

Formation of a gold–carbon dot nanocomposite with superior catalytic ability for the reduction of aromatic nitro groups in water

We report the synthesis of a gold–carbon dot nanocomposite and its utility as a recyclable catalyst for the reduction of aromatic nitro groups. The presence of carbon dots on gold nanosurfaces enhanced the reduction rate by two-fold.

Probing on green long persistent Eu2+/Dy3+ doped Sr3SiAl4O11 emerging phosphor for security applications

Herein, a novel green emitting long-persistent Sr3SiAl4O11:Eu2+/Dy3+ phosphor was synthesized in a single phase form using facile solid state reaction method under the reducing atmosphere of 10% H2 and 90% N2. The resulting phosphor exhibits hyper-sensitive strong broad green emission, peaking at 510 nm upon 340 nm excitation wavelength, which is attributed to the 4f65d1-4f7 transitions of emission center of europium (Eu2+) ions. Moreover, the incorporation of dysprosium (Dy3+) ions, which act as effective hole trap centers with appropriate depth, largely enhances the photoluminescence characteristics and greatly improves the persistent intense luminescence behavior of Sr3SiAl4O11:Eu2+/Dy3+ phosphor under ultraviolet (UV) excitation. In addition, with the optimum doping concentration and sufficient UV excitation time period, the as-synthesized phosphor can be persisted afterglow for time duration ∼4 h with maximum luminescence intensity. Thus, these results suggest that this phosphor could be expected as ...