Coupling single quantum dots to plasmonic nanocones: optical properties

Abstract

Coupling a single quantum emitter, such as a fluorescent molecule or a quantum dot (QD), to a plasmonic nanostructure is an important issue in nano-optics and nano-spectroscopy, relevant for a wide range of applications, including tip-enhanced near-field optical microscopy, plasmon enhanced molecular sensing and spectroscopy, and nanophotonic amplifiers or nanolasers, to mention only a few. While the field enhancement of a sharp nanoantenna increasing the excitation rate of a very closely positioned single molecule or QD has been well investigated, the detailed physical mechanisms involved in the emission of a photon from such a system are, by far, less investigated. In one of our ongoing research projects, we try to address these issues by constructing and spectroscopically analysing geometrically simple hybrid heterostructures consisting of sharp gold cones with single quantum dots attached to the very tip apex. An important goal of this work is to tune the longitudinal plasmon resonance by adjusting the cones' geometry to the emission maximum of the core-shell CdSe/ZnS QDs at nominally 650 nm. Luminescence spectra of the bare cones, pure QDs and hybrid systems were distinguished successfully. In the next steps we will further investigate, experimentally and theoretically, the optical properties of the coupled systems in more detail, such as the fluorescence spectra, blinking statistics, and the current results on the fluorescence lifetimes, and compare them with uncoupled QDs to obtain a clearer picture of the radiative and non-radiative processes.

Shaping and polarizing fluorescence emission of a polycrystalline organic semiconductor film by plasmonic nanogratings

“…4. Due to the modification of the local density of optical states by the plasmon resonance and the antenna properties of the plasmonic nanostructures, the fluorescence in the hybrid system appears to be increased [4,5,7,37,38]. For the wires with 63 and 74 nm widths, the left shoulder of the broad fluorescence curve of DIP at around 630 nm is most strongly enhanced (Fig.…”

“…Several mechanisms can lead to the fluorescence enhancement in the hybrid system: the increase of light absorption by the DIP molecules due to the enhanced near-field at the surface of the plasmonic nanostructures, changes of the radiative and non-radiative transition rates induced by the metal nanostructures, and/or the coupling of the nanostructures' near-field to the far-field [6,7,37,38]. Because of the unpolarized excitation in the fluorescence setup, a potential absorption effect should be visible in both the TE-and TM-polarized emission data (Fig.…”

“…In further experiments, time and polarization-dependent measurements could be used for further investigation of the change of the transition rates and decay channels due to the metallic grating [7,38]. With such measurements, the lifetime modification due to the change of the local electromagnetic density of states can be investigated.…”

“…Through this associated near-field, localized surface plasmons can couple to adjacent materials and vice versa [4,5]. Thus, in hybrid systems with fluorescent molecules or quantum dots, plasmonic nanostructures can enhance and spectrally shape the spontaneous emission [5][6][7][8]. For quantum dots or fluorophores, the polarizability and directionality of the fluorescence emission by plasmonic nanoantennas has been demonstrated [9][10][11].…”

Collective Effects in Second-Harmonic Generation from Plasmonic Oligomers

“…Because of these intriguing characteristics, CVBs are used as novel probes for imaging the orientation of molecules or nanostructures. 29 − 33 Owing to the tensorial character of nonlinear interactions, CVBs are also used to improve the orientation sensitivity of nonlinear microscopy techniques. 34 − 39 In the context of oligomer studies, focused CVBs have been shown to excite collective dark modes (with zero net dipole moment), which cannot be accessed using linear polarization under normal incidence.…”