Fabrication and Electro-optic Properties of MWCNT Driven Novel Electroluminescent Lamp

We present a novel, cost-effective and facile technique, wherein multi-walled carbon nano-tubes (CNTs) were used to transform a photoluminescent material to exhibit stable and efficient electroluminescence (EL) at low-voltages. As a case study, a commercially available ZnS:Cu phosphor (P-22G) was combined with a very low concentration of CNTs dispersed in ethanol and its alternating current driven electroluminescence (AC-EL) is demonstrated. The role of CNTs has been understood as a local electric field enhancer and facilitator in the hot carrier injection inside the ZnS crystal to produce EL in the hybrid material. The mechanism of EL is discussed using an internal field emission model, intra-CNT impact excitation and the recombination of electrons and holes through the impurity states.Comment: 9 Figure

Piperidinols that show anti-tubercular activity as inhibitors of arylamine N-acetyltransferase: an essential enzyme for mycobacterial survival inside macrophages

Latent M. tuberculosis infection presents one of the major obstacles in the global eradication of tuberculosis (TB). Cholesterol plays a critical role in the persistence of M. tuberculosis within the macrophage during latent infection. Catabolism of cholesterol contributes to the pool of propionyl-CoA, a precursor that is incorporated into cell-wall lipids. Arylamine N-acetyltransferase (NAT) is encoded within a gene cluster that is involved in the cholesterol sterol-ring degradation and is essential for intracellular survival. The ability of the NAT from M. tuberculosis (TBNAT) to utilise propionyl-CoA links it to the cholesterol-catabolism pathway. Deleting the nat gene or inhibiting the NAT enzyme prevents intracellular survival and results in depletion of cell-wall lipids. TBNAT has been investigated as a potential target for TB therapies. From a previous high-throughput screen, 3-benzoyl-4-phenyl-1-methylpiperidinol was identified as a selective inhibitor of prokaryotic NAT that exhibited antimycobacterial activity. The compound resulted in time-dependent irreversible inhibition of the NAT activity when tested against NAT from M. marinum (MMNAT). To further evaluate the antimycobacterial activity and the NAT inhibition of this compound, four piperidinol analogues were tested. All five compounds exert potent antimycobacterial activity against M. tuberculosis with MIC values of 2.3-16.9 µM. Treatment of the MMNAT enzyme with this set of inhibitors resulted in an irreversible time-dependent inhibition of NAT activity. Here we investigate the mechanism of NAT inhibition by studying protein-ligand interactions using mass spectrometry in combination with enzyme analysis and structure determination. We propose a covalent mechanism of NAT inhibition that involves the formation of a reactive intermediate and selective cysteine residue modification. These piperidinols present a unique class of antimycobacterial compounds that have a novel mode of action different from known anti-tubercular drugs

Fabrication and electro-optic properties of a MWCNT driven novel electroluminescent lamp

We present a novel, cost-effective and facile technique, wherein multi-walled carbon nanotubes (CNTs) were used to transform a photoluminescent material to exhibit stable and efficient electroluminescence (EL) at low voltages. As a case study, a commercially available ZnS:Cu phosphor (P-22G having a quantum yield of 65 +/- 5%) was combined with a very low (similar to 0.01 wt%) concentration of CNTs dispersed in ethanol and its alternating current driven electroluminescence (AC-EL) is demonstrated. The role of CNTs has been understood as a local electric field enhancer and facilitator in the hot carrier injection inside the ZnS crystal to produce EL in the hybrid material. The mechanism of EL is discussed using an internal field emission model, intra-CNT impact excitation and the recombination of electrons and holes through the impurity states

Investigation of Local Field Enhancement and Hot Electron Injection in Carbon Nano-Tube Doped Phosphor Nano-Composite for Ultra-Bright Electroluminescence

Present work focuses on the effective doping of multi-walled carbon nanotube (CNT) in the ZnS:Cu phosphor nano-composite and thereafter improvement in the optical performance of electroluminescent (EL) device due to increased local field effects. To facilitate doping of CNTs into the phosphor and decrease the operating voltage of the EL device, CNTs were shortened by milling and incorporated effectively using a flux assisted solid-state annealing reaction. Interestingly shorter the length of CNTs used; greater was the local field enhancement, improvement in brightness and efficiencies observed for the EL devices. When the field is applied, adequate charge carriers tunnel into the ZnS:Cu system through the tips of the CNTs by forming high energy hot spots thus enhancing the local field. The improved device characteristics are due to field enhancement and effective transfer of energy from hot spots to copper activator by impact ionization. The detailed electrical characterization of the novel EL device along with its brightness measurements are presented by considering the hot electron injection model

Studies on phase stability, mechanical, optical and electronic properties of a new Gd2CaZnO5 phosphor system for LEDs

A new ternary oxide Gd2CaZnO5 having interesting structural, mechanical, electronic and optical properties is synthesized and is studied in detail using density functional theory. The analysis revealed two polymorphs: orthorhombic and tetragonal; the orthorhombic phase was found to be the most stable structure under ambient conditions. A high-pressure (hydrostatic) phase transition to the tetragonal phase is predicted at about 4 GPa. This is one of very few reports that depict the phase transition of oxide materials under pressure. The calculated results are in agreement with the X-ray diffraction studies supported by Rietveld analysis. Analysis of the optical properties revealed both polymorphs to be direct-gap semiconductors with low dielectric constants. The calculated elastic constants of both phases satisfy the mechanical stability criteria. It is also identified that the half-filled 4f orbital of Gd induces a strong magnetic spin polarization in the host oxide lattice indicating that the material could be effectively used in versatile applications ranging from biomedical devices to light emitting diodes

Probing the structure, morphology and multifold blue absorption of a new red-emitting nanophosphor for LEDs

There has been a stringent demand for blue (similar to 450 to 470 nm) absorbing and red (similar to 611 nm) emitting material systems in phosphor converted white light emitting diodes (WLEDs) available in the market. The conventionally used red-emitting Y2O3:Eu3+ phosphor has negligible absorption for blue light produced by GaInN based LED chips. To address this issue, a new red-emitting Gd2CaZnO5:Eu3+ (GCZO:Eu3+) nanophosphor system having exceptionally strong absorption for blue (similar to 465 nm) and significant red (similar to 611 nm) photoluminescence is presented. This is attributed to a dominant f-f transition (D-5(0) -> F-7(2)) of Eu3+ ions, arising due to an efficient energy transfer from the Gd3+ sites of the host lattice to Eu3+ ions. The external quantum yield (QY) measured at 465 nm absorption and 611 nm emission revealed that the GCZO: Eu3+ nanophosphor has better QY of 23% as compared to commercial Y2O3:Eu3+, which is <1%. X-ray diffraction and microscopy observations showed the nanocrystalline nature and slightly elongated morphology of the sample, respectively. While the energy dispersive X-ray analysis identified the chemical constituents of the GCZO: Eu3+ nanophosphor, the color overlay imaging confirmed the substitution of Eu3+ for Gd3+ ions. As seen from the QY statistics it is highly anticipated that the multifold absorption at similar to 465 nm would certainly improve the color rendering properties of existing WLEDs

High yield synthesis and characterization of aqueous stable zinc oxide nanocrystals using various precursors

We report a high (similar to 94%) yield synthesis of intrinsic zinc oxide (ZnO) nanocrystal powders having crystallite sizes in the range 13-35 nm using a novel gel-incineration method with inexpensive precursor salts and citric acid as chelating agent. The influence of various precursor chemicals on the nanocrystallite size, morphology and luminescent properties has been studied in detail. It was identified that the ZnO nanocrystals prepared using organic precursor resulted the smallest crystallite size as compared to inorganic precursors. Reaction temperature was optimized to be similar to 900 degrees C by simultaneous thermogravimetric analysis and differential scanning calorimetry studies. Morphology and microstructure of the ZnO nanocrystals have been studied using a scanning electron microscopy. Analysis of photoluminescence excitation and emission spectra enabled us to calculate the band gap energy and defect analysis of as prepared ZnO nanocrystals respectively. The stability of ZnO nanocrystals in water has been verified on time scale and its potential use has been successfully demonstrated for security marker applications

High yield synthesis and characterization of aqueous stable zinc oxide nanocrystals using various precursors

We report a high (similar to 94%) yield synthesis of intrinsic zinc oxide (ZnO) nanocrystal powders having crystallite sizes in the range 13-35 nm using a novel gel-incineration method with inexpensive precursor salts and citric acid as chelating agent. The influence of various precursor chemicals on the nanocrystallite size, morphology and luminescent properties has been studied in detail. It was identified that the ZnO nanocrystals prepared using organic precursor resulted the smallest crystallite size as compared to inorganic precursors. Reaction temperature was optimized to be similar to 900 degrees C by simultaneous thermogravimetric analysis and differential scanning calorimetry studies. Morphology and microstructure of the ZnO nanocrystals have been studied using a scanning electron microscopy. Analysis of photoluminescence excitation and emission spectra enabled us to calculate the band gap energy and defect analysis of as prepared ZnO nanocrystals respectively. The stability of ZnO nanocrystals in water has been verified on time scale and its potential use has been successfully demonstrated for security marker applications