Meg Mahat

Competition Between Resonant Plasmonic Coupling and Electrostatic Interaction in Reduced Graphene Oxide Quantum Dots

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.

Electrostatic enhancement of light emitted by semiconductor quantum well

Carrier dynamics in metal-semiconductor structures is driven by electrodynamic coupling of carriers to the evanescent field of surface plasmons. Useful modifications in electron and hole dynamics due to presence of metallic inclusions show promise for applications from light emitters to communications. However, this picture does not include contributions from electrostatics. We propose here an electrostatic mechanism for enhancement of light radiated from semiconductor emitter which is comparable in effect to plasmonic mechanism. Arising from Coulomb attraction of e-h pairs to their electrostatic images in metallic nanoparticles, this mechanism produces large carrier concentrations near the nanoparticle. A strong inhomogeneity in the carrier distribution and an increase in the internal quantum efficiency are predicted. In our experiments, this manifests as emission enhancement in InGaN quantum well (QW) radiating in the near-UV region. This fundamental mechanism provides a new perspective for improving the efficiency of broadband light emitters.

Dual Pump Femtosecond Laser Induced Plasma

Laser-induced breakdown spectroscopy (LIBS) can provide a noncontact way of inspecting a specimen including distinct signature of atomic composition of the sample. Ultra-short pulse laser enables characterization of any materials by utilizing the multiphoton process, which is a dominant carrier generation mechanism for dielectric materials. Additionally, femtosecond LIBS yields low background and better defined atomic lines than the nanosecond LIBS. We have performed a time-resolved emission intensity measurement for an iron oxide (Fe3O4, magnetite). The emission intensity has the peak value at 100 ps time delay, signifying that the succeeding pump beam is interacting with the plasma generated in the vicinity of the sample by the preceding beam. The dual pulses significantly enhance the atomic emission as compared to single pulse excitation and enables ultrafast time-resolved spectroscopy.Copyright