ABSTRACT
A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu3+ (SSO:xEu3+, x = 1.0, 2.0 and 5.0%), were synthesized by a sol-gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic α'-SSO and monoclinic ß-SSO phases of the SSO:xEu3+ phosphors. When SSO:xEu3+ phosphors are excited under ultraviolet (UV) light (λ = 250 nm, ~ 4.96 eV), they emit yellow (~ 590 nm), orange (~ 613 nm) and red (~ 652 and 703 nm) PL bands. These PL emissions typically correspond to 4f-4f electronic transitions that involve the multiple excited 5D0 â 7FJ levels (J = 1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu3+ phosphors is strongly related to the local electronic/atomic structures of the Eu3+-O2- associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and Kα X-ray emission spectroscopy. In the synthesis of SSO:xEu3+ phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the Eu 5d and/or O 2p-Eu 4f/5d states (mostly the O 2p-Eu 5d states) to the 5D0 levels, facilitating the recombination of electrons that have transitioned from the 5D0 level to the 7FJ level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO:xEu3+ phosphors. This PL-related behavior indicates that SSO:xEu3+ phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.
ABSTRACT
The rational approach motivated the design of novel antimicrobial silver and silver-copper bimetallic nanoparticles contained within zeolitic imidazolate framework-8 supported on graphene oxide (GO), Ag@ZIF-8@GO, and AgCu@ZIF8@GO. In the resultant composites, ZIF-8 was able to prevent the stacking of GO sheets and also acted as a carrier for the nanoparticles within its cavities. GO, on the other hand, acted as an anchoring support enabling uniform dispersion of the nanocomposites, thus eliminating their aggregation. The morphological and physicochemical properties of the composites were determined through a variety of characterization techniques, for example, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, p-X-ray diffraction (XRD), nitrogen sorption, and X-ray photoelectron spectroscopy (XPS). The energy-dispersive system and XPS supplied evidence of the presence of all expected components in the composites. The XRD provided proof of a crystalline, distorted ZIF-8 structure. Ag@ZIF8@GO and Ag-Cu@ZIF-8@GO composites were effective against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria as determined by the disc diffusion method. The role of silver nanoparticles (AgNPs) in the antibacterial activity of both Ag@ZIF8@GO and AgCu@ZIF8@GO was highlighted as crucial in the probable pathway in the antimicrobial activity of the composites.
ABSTRACT
The electrical conduction mechanisms were investigated for the CdS and Cu-doped CdS (CdS:Cu) nanoparticles embedded in polyvinyl alcohol (PVA) (PVA/CdS and PVA/CdS:Cu) nanocomposites; synthesized by the chemical Sol Gel method on indium tin-oxide (ITO) substrate. X-ray diffraction pattern results show that the PVA/CdS nanocomposite is hawleyite-sturcture and PVA/CdS:Cu nanocomposites show greenockite-hawelyite mixed structure. The sizes of CdS and CdS:Cu nanoparticles were estimated from transmission electron microscopy (TEM) images and are ≈4 nm and ≈10 nm respectively; which were formed inside the PVA polymer layer. The devices were fabricated with Ag and ITO as electrodes with PVA/CdS and PVA/CdS:Cu nanocomposites as an active layers. The current-voltage (I-V ) relationships measurements shows the nature is extended memrisitve features for both PVA/CdS and PVA/CdS:Cu nanocomposites. The ION/IOFF ratios are enhanced and become more prominent in case of PVA/CdS:Cu nanocomposites device. The resistive switching characteristic show Schottky, Trapped-charge limited current (TCLC) and Space charge limited conduction (SCLC) mechanisms in Ag/PVA/CdS/ITO device; whereas Schottky, Ohmic, TCLC and SCLC were observed in Ag/PVA/CdS:Cu/ITO device.
ABSTRACT
Vertically aligned multi-walled carbon nanotubes (CNTs) were grown on p-type silicon wafer using thermal chemical vapor deposition process and subsequently treated with oxygen plasma for oxidation. It was observed that the electron field emission (EFE) characteristics are enhanced. It showed that the turn-on electric field (E(TOE)) of CNTs decreased from 0.67 (untreated) to 0.26 V/microm (oxygen treated). Raman spectra showed that the numbers of defects are increased, which are generated by oxygen-treatment, and absorbed molecules on the CNTs are responsible for the enhancement of EFE. Scanning electron microscopy and Transmission electron microscopy images were used to identify the quality and physical changes of the nanotube morphology and surfaces; revealing the evidence of enhancement in the field emission properties after oxygen-plasma treatment.
Subject(s)
Nanotubes, Carbon , Microscopy, Electron, Scanning , Microscopy, Electron, Transmission , Oxidation-Reduction , Spectrum Analysis, RamanABSTRACT
This work elucidates the electronic structure, electron field emission and magnetic anisotropic behaviors of single wall carbon nanotubes (SWCNTs) for the spin-electronics device application grown on the La0.66Sr0.33MnO3 (LSMO)/SrTiO3 (STO) substrate. Micro-Raman spectroscopy, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES) were used for the study of electronics structure. The field emission characteristics were studied from the electron field emission current density (J) versus applied electric field (E(A)) from which the turn-on electric field (E(TOE)) was evaluated. The magnetization behaviors are also presented by the M-H hysteresis loop and were obtained by applying the magnetic field in the parallel and perpendicular direction of the CNTs at 305 K and 5 K temperatures. A magnetic measurement shows that the coercivity of the CNTs/LSMO/STO is higher and has hig anisotropic-nature than the composite LSMO/STO that could be the good material for the future possible spin-electronics device applications.
ABSTRACT
This work elucidates the effects of high-temperature annealing on the microscopic and electronic structure of multiwalled carbon nanotubes (MWCNTs) using high-resolution transmission electron microscopy, micro-Raman spectroscopy, X-ray diffraction, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES), respectively. The field emission and magnetization behaviors are also presented. The results of annealing are as follows: (1) MWCNTs tend to align in the form of small fringes along their length, promote graphitization and be stable in air, (2) XANES indicates an enhancement in oxygen content on the sample, implying that it can be adopted for sensing and storing oxygen gas, (3) the electron field emission current density (J) is enhanced and the turn-on electric field (E(TOE)) reduced, suggesting potential use in field emission displays and as electron sources in microwave tube amplifiers and (4) as-grown MWCNTs with embedded iron nanoparticles exhibits significantly higher coercivity approximately 750 Oe than its bulk counterpart (Fe(bulk) approximately 0.9 Oe), suggesting its potential use as low-dimensional high-density magnetic recording media.
