Manoranjan Ghosh

Role of ambient air on photoluminescence and electrical conductivity of assembly of ZnO nanoparticles

Effect of ambient gases present in air on photoluminescence (PL) and electrical conductivity of films prepared using ZnO nanoparticles (NPs) have been investigated. It is observed that NPs of size below 20 nm kept inside a chamber exhibit complete reduction in their visible PL when oxygen partial pressure of the surrounding gases is decreased by evacuation. However, the visible PL from ZnO NPs is insensitive to other major gases present in the ambient air. The rate of change of PL intensity with pressure is inversely proportional to the ambient air pressure and increases when particle size decreases due to the enhanced surface to volume ratio. On the other hand, an assembly of ZnO NPs behaves as a complete insulator in the presence of dry air and its major components like N2, O2, and CO2. Electrical conduction having resistivity ∼102–103 Ωm is observed in the presence of humid air. The depletion layer formed at the NP surface after acquiring donor electrons of ZnO by the adsorbed oxygen has been found to ...

Optimal electron irradiation as a tool for functionalization of MoS2: Theoretical and experimental investigation

We demonstrate the utility of electron irradiation as a tool to enhance device functionality of graphene-analogous MoS2. With the help of first-principles based calculations, vacancy-induced changes of various electronic properties are shown to be a combined result of crystal-field modification and spin-orbital coupling. A comparative theoretical study of various possible vacancy configurations both in bulk and monolayer MoS2 and related changes in their respective band-structures help us to explain plausible irradiation induced effects. Experimentally, various structural forms of MoS2 in bulk, few layered flakes, and nanocrystals are observed to exhibit important modification of their magnetic, transport, and vibrational properties, following low doses of electron irradiation. While irradiated single crystals and nanocrystals show an enhanced magnetization, transport properties of few-layered devices show a significant increase in their conductivity, which can be very useful for fabrication of electronic...

Photovoltaic Properties Of ZnO Nanoparticle Based Solid Polymeric Photoelectrochemical Cells

In this work, we report optical and photovoltaic properties of ZnO based solid polymeric photoelectrochemical (PEC) cell. In this device construction, film of ZnO nanoparticle (NP) has been sandwiched between ITO and LiClO4‐PEO solid electrolyte. ZnO NP has been used as photo‐anode and the electrolyte LiClO4 has been dissolved in a solid solution polyethylene oxide that makes the device lightweight and portable. The charge transfer is performed by Li+ and ClO4− ions which serve the purpose of a redox couple in a conventional dye sensitize solar cell (DSSC). Short Circuit Current (JSC) shows maximum when the ZnO/ITO interface has been illuminated by a UV light (350±15 nm) passing through the transparent ITO glass substrate. JSC and Open Circuit Voltage (VOC) of the best performing device are found to be 7 μA/cm2 and 0.24 V respectively under white light of intensity 15 mW/cm2.

Growth and optical properties of partially transparent Eu doped CaF2 ceramic

Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size∼12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

PERFORMANCE COMPARISON OF p–n JUNCTION DIODES USING ZINC OXIDE AND COPPER PHTHALOCYANINE HYBRID NANOCOMPOSITES AND BILAYER HETEROSTRUCTURES

Nanocomposites of n-type Zinc Oxide (ZnO) and p-type copper phthalocyanine (CuPc) were synthesized using solution route and the electrical properties of heterojunctions of ZnO and CuPc in the nanocomposite film was studied. For comparison, electrical properties of bilayer heterojunction devices using ZnO nanostructure drop cast film and thermally evaporated CuPc were also studied. Rectification ratio (RR) of about 28 and 5.5 was obtained at 4 V for devices with nanocomposite film and bilayer heterojunctions indicating improved formation of p–n junction characteristics for nanocomposite films. Values of ideality factor, barrier height at the p–n junction interface and series resistance were estimated using different methods like semilog plots, Cheung and Nordes methods. Ideality factor estimated from semilog plots and Cheungs methods were found to be higher than unity indicating deviation from ideal diode behavior. Barrier height estimated from different methods was about 0.7 eV. Series resistance measur...

Synthesis of gadolinium silicate by hydrothermal method

A simple method based on hydrothermal synthesis of materials to prepare gadolinium silicate has been prescribed. It is found that molar ratio of Gd(NO3)3: TEOS plays a crucial role in the formation of Gd2SiO5. The effect of calcinations, concentration of the precipitating agent and dopant atoms on composition and morphology of the synthesized materials has been investigated. The desired phase of Gd2SiO5 can be synthesized from hydrothermally grown powder after annealing at 1400°C.

Organic–Inorganic Composite Films Based on Gd3Ga3Al2O12:Ce Scintillator Nanoparticles for X-ray Imaging Applications

Organic-inorganic nanocomposite self-standing films of Gd3Ga3Al2O12 (GGAG) uniformly dispersed in poly(methyl methacrylate) (PMMA) and polystyrene polymer are prepared for radiography application. GGAG:Ce nanoscintillator has been chosen because of its high light output and fast decay time. The nanopowder of GGAG is synthesized by coprecipitation method and dispersed in the polymer matrix by a simple blending technique. The nanocomposite films of thickness in the range of 150-450 μm with a very high inorganic content is achieved by this technique. These films are characterized by their uniformity, optical absorption, photoluminescence, and radioluminescence. These films are further tested for their application in radiography by recording X-ray images using a commercially available charge-coupled device camera. A resolution of 10 lp/mm is obtained using GGAG:PMMA composite film with 50% loading, confirming their application in imaging devices.

Band-gap modulation via gallium substitution in cerium doped gadolinium aluminum garnet using a mixed fuel combustion approach

Cerium doped Gadolinium garnets (Gd3AlxGa5−xO12 where 0≤x≤5) are synthesized via combustion synthesis using mixture of urea and glycine fuels. A 4h Post annealing at 1400 oC is found to be necessary for pure phase formation. Lattice spacing variation as a result of partial or total Ga substitution at Al site was mapped by X-ray diffraction. Photoluminescence emission of Ce shifts as a consequence of Ga substitution and therefore suggests a local re-adjustment of crystal field around activator site.

Size dependent absorption kinetics of sedimenting nanoparticles

Nanoparticles (NPs) beyond a certain size suspended in a lighter fluid medium, fall under gravity after attaining terminal velocity. This velocity is higher for larger particles. Thus absorption kinetics of ZnO NPs reflecting a change in the particle density with time exhibit different slopes for different sizes. A model based on Stoke’s law of viscous drag can predict the size distribution of NPs having negligible inter-particle correlations. However, distinct slopes of the absorption kinetics provide a rough idea of the average size of as grown NPs.

Effect of site selective Ti substitution on the melting point of CuTi alloys

In this work, the effect of site-selective substitution of Ti in Cu on the thermal stability of CuTi alloy has been investigated using classical molecular dynamics simulations with Embedded Atom Method potentials. For random substitution, the melting point decreases linearly with increase in Ti concentration. A non monotonous dependence is seen when Cu atoms at selective sites are replaced by Ti. For a particular doping concentration, the melting point shows a wide range of variation depending on the order of atomic arrangement and can be fine tuned by selecting the site of the substitution. The variations in melting point in different cases have been explained in terms of the peak height, width and position of their corresponding radial distribution functions.