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.

The absorption in quantum dots (QDs) embedded within a semiconductor matrix can be manipulated by resonant optical excitation of phonons. The far-field interaction of the light leading to dressed phonon states within reduced graphene oxide quantum dots has been coherently modified by a near-field optical driving field at the nanoscale limit. The near-field optical excitation was introduced by resonant excitation of localized plasmons in metal nanoparticles coupled to QDs for ultrafast light manipulation. The coherent interaction of photons due to localized plasmon induced a change in the transient absorption of graphene oxide quantum dots conjugated to silver nanoparticles. Resonant pumping of plasmons and phonons with 400 nm pump photons induces a coherent change in excitonic absorption within QDs which results in phonon-assisted plasmon induced transparency at room temperature. This novel effect can be related to the appearance of the coherent effects such as forming dark states and coherent population trapping related to Fano interference. A large Rabi splitting of 120 meV has been observed within 800 fs of the preparation of the dressed phonon–photon states. A theoretical model has been developed to quantitatively demonstrate that the dark states can be still formed at ultrashort time scale corresponding to the dephasing time of the carriers in the QDs.

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