A fully oxidized state of graphene behaves as a pure insulating while a pristine graphene behaves as a pure conducting. The in-between oxide state in graphene which is the controlled state of oxide behaves as a semiconducting. This is the key condition for tuning optical band gap for the better light emitting property. The controlling method of oxide in graphene structure is known as reduction which is the mixed state of sp2 and sp3 hybrid state in graphene structure. sp2 hybridized domains correspond to pure carbon-carbon bond i.e. pristine graphene while sp3 hybridized domains correspond to the oxide bond with carbon i.e. defect in graphene structure. This is the uniqueness of the graphene-base material. Graphene is a gapless material i.e. having no bandgap energy and this property prevents it from switching device applications and also from the optoelectronic devices applications. The main challenge for this material is to tune as a semiconducting which can open the optical characteristics and emit light of desired color. There may be several possibilities for the modification of graphene-base material that can tune a band gap. One way is to find semiconducting property by doping the defects into pristine graphene structure. Other way is oxides functional groups in graphene structure behaves as defects. The physical properties of graphene depend on the amount of oxides present in graphene structure. So if there are more oxides in graphene structure then this material behaves as a insulating. By any means if it can be reduced then oxides amount to achieve specific proportion of sp2 and sp3 that can emit light of desired color. Further, after achieving light emission from graphene base material, there is more possibility for the study of non-linear optical property. In this work, plasmonic effect in graphene oxide has been focused. Mainly there are two kinds of plasmon effects have been studied, one is long range (surface) and short range (localized) plasmon. For long range plasmon gold thin film was deposited on partially reduced graphene oxide and for short range plasmon silver nanoparticles have used. Results show that there are 10-fold enhancement in light emission from partial graphene oxide coated with gold thin film while 4-fold enhancement from reduced graphene oxide solution with silver nanoparticles. Chemical method and photocatalytic method have been employed for the reduction of graphene oxide for the study of surface plasmon and localized plasmon. For the characterization UV-Vis spectrometer for absorption, spectrofluorophotometer for fluorescent emission, Raman spectrometer for material characterization, photoluminescence and time resolved photoluminescence have been utilized. Silver and gold nanoparticles are spherical of average size of 80 nm and 40 nm have been used as plasmons.
Polymer assisted spherical FeNi nanoparticles were prepared via wet chemical method using hydrazine as a reducing agent and polymers (PVP and PEG) as reducing and stabilizing agent. Structural studies performed using XRD and TEM shows uniform dispersion of fine FeNi nanocrystallites in nanocomposite particles. The size and thermal stability of FeNi nanoparticles prepared under same reaction condition was found to be dependent on the type and the molecular weight of the polymer used. However, the magnetic properties of nanocomposite particles were not influenced by the polymers. The study highlights subtle differences in using polymers during the synthesis of alloyed nanocomposite particles.
The absorption due to phonon vibrations in graphene oxide quantum dots (GO-QDs) has been modified by localized plasmons induced by Ag nanoparticles (NPS). The interference of phonons and plasmons results in coherent interaction that leads to the formation of "dark states" and "coherent population trapping" related to Fano like effect. The localized electric field effectively drives the phonons which in turn modifies the coherent interaction in exciton absorption states of graphene oxide. A quantum optical theory is used to qualitatively explain the differential absorption spectra measured using pump-probe spectroscopy demonstrating the formation of dark states.
Abstract The light emission from reduced graphene oxide quantum dots (rGO-QDs) exhibit a significant enhancement in photoluminescence (PL) due to localized surface plasmon (LSP) interactions. Silver and gold nanoparticles (NPs) coupled to rGO nanoparticles exhibit the effect of resonant LSP coupling on the emission processes. Enhancement of the radiative recombination rate in the presence of Ag-NPs induced LSP tuned to the emission energy results in a four-fold increase in PL intensity. The localized field due to the resonantly coupled LSP modes induces n-π* transitions that are not observed in the absence of the resonant interaction of the plasmons with the excitons. An increase in the density of the Ag-NPs result in a detuning of the LSP energy from the emission energy of the nanoparticles. The detuning is due to the cumulative effect of the red-shift in the LSP energy and the electrostatic field induced blue shift in the PL energy of the rGO-QDs. The detuning quenches the PL emission from rGO-QDs at higher concentration of Ag NPs due to non-dissipative effects unlike plasmon induced Joule heating that occurs under resonance conditions. An increase in Au nanoparticles concentration results in an enhancement of PL emission due to electrostatic image charge effect.
Anthracene-doped polyphenylsiloxane (PPS) glass containing silver nanoparticles (AgNPs) of appropriate size was synthesized in a form of solid thin films for modifying light emission characteristics. The photoluminescence (PL) emission from the anthracene molecules at ~2.95 eV was resonantly coupled to the localized surface plasmon (LSP) polariton modes that were induced by the excitation of ~30 nm sized AgNPs. The increase in absorption of incident photons within a highly scattering medium, energy transfer from the localized excitons to the LSP modes, and the electrostatic Coulomb effects of the excitons in the presence of metal NPs all resulted in a significant enhancement of PL emission. The PL enhancement is dependent on the concentration of the anthracene molecules. The integrated PL intensity enhancement at the optimum concentration of anthracene molecules in the PPS glass with AgNPs is found to exceed 50.
We investigate properties of reduced graphene oxide films in the THz frequency range. We demonstrate tuning their conductivity and THz attenuation by reduction as well as by intercalation of metals. These findings suggest that graphene oxide holds promise for electromagnetic interference shielding and other THz device applications.
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