Sergey V. Gaponenko

All-dielectric one-dimensional periodic structures for total omnidirectional reflection and partial spontaneous emission control

A remarkable property of one-dimensional (I-D) alldielectric periodic structures has recently been reported, namely, a 1-D structure can totally reflect electromagnetic wave of any polarization at all angles within a prescribed frequency region, Unlike their metallic counterpart, such all-dielectric omnidirectional mirrors are nearly free of loss at optical frequencies. Here we discuss the physics, design criteria and applications of the thin-film all-dielectric omnidirectional mirror. The experimental demonstration of the mirror is presented at optical frequencies.

Spontaneous emission of dye molecules, semiconductor nanocrystals, and rare-earth ions in opal-based photonic crystals

Photonic crystals based on silica colloidal crystals (artificial opals) exhibit pronounced stopbands for electromagnetic wave propagation and the corresponding modification of the photon density of states in the visible range. These spectrally selective features can be enhanced by impregnating opals with higher refractive materials like, e.g., polymers. Doping of these structures with dye molecules, semiconductor nanoparticles (quantum dots), and rare-earth ions provides a possibility to examine the challenging theoretical predictions of the inhibited spontaneous emission in photonic bandgap (PBG) materials. First experiments are discussed in which pronounced modification of spontaneous emission spectra and noticeable changes in decay kinetics were observed.

Anisotropic emission from multilayered plasmon resonator nanocomposites of isotropic semiconductor quantum dots.

We propose and demonstrate a nanocomposite localized surface plasmon resonator embedded into an artificial three-dimensional construction. Colloidal semiconductor quantum dots are assembled between layers of metal nanoparticles to create a highly strong plasmon-exciton interaction in the plasmonic cavity. In such a multilayered plasmonic resonator architecture of isotropic CdTe quantum dots, we observed polarized light emission of 80% in the vertical polarization with an enhancement factor of 4.4, resulting in a steady-state anisotropy value of 0.26 and reaching the highest quantum efficiency level of 30% ever reported for such CdTe quantum dot solids. Our electromagnetic simulation results are in good agreement with the experimental characterization data showing a significant emission enhancement in the vertical polarization, for which their fluorescence decay lifetimes are substantially shortened by consecutive replication of our unit cell architecture design. Such strongly plasmon-exciton coupling nanocomposites hold great promise for future exploitation and development of quantum dot plasmonic biophotonics and quantum dot plasmonic optoelectronics.

Nonresonant Surface-Enhanced Raman Scattering of ZnO Quantum Dots with Au and Ag Nanoparticles

Pronounced 10(4)-fold enhancement of Raman scattering has been obtained for ZnO nanocrystals on substrates coated with 50 nm Ag nanoparticles under nonresonant excitation with a commercial red-emitting laser. This makes feasible beyond 10(-18) mole detection of ZnO nanocrystals with a commercial setup using a 0.1 mW continuous wave laser and can be purposefully used in analytical applications where conjugated nanocrystals serve as Raman markers. For Au-coated surfaces the enhancement is much lower and the heating effects in the course of Raman experiments are pronounced.

Spectral scalability as a result of geometrical self-similarity in fractal multilayers

The optical spectra of fractal multilayer dielectric structures have been shown to possess spectral scalability, which has been found to be directly related to the structures spatial (geometrical) self-similarity. Phase and amplitude scaling relations, as well as effects of finite structure size, have been derived.

Nonlinear-optical properties of semiconductor quantum dots and their correlation with the precipitation stage

We present nanosecond hole-burning experiments for CdSxSe1−x and CdSe quantum dots grown in a glass matrix; we compare the results for different precipitation stages. For the first time to our knowledge a drastic sharpening of the spectral holes with a half-width as low as 10 meV has been found to be typical for the samples prepared in the nucleation and the normal growth stages, whereas structures grown in the coalescent stage show only broadband nonlinear absorption. The spectral width of the holes is highly sensitive to the illumination history, particularly in the case of small-size quantum dots. A coexistence of quantum dots from the coalescent and the noncoalescent growth regimes results in a structured nonlinear absorption spectrum from the superposition of the corresponding broadband and narrow-line nonlinear spectra; thus the actual electronic-level structure can be completely masked. The differences in the linewidth are attributed to different mechanisms of surface construction or reconstruction during the growth process or after strong laser exposure, leading to different surface properties such as localized states or spatial charge distributions, which in turn give rise to different mechanisms of line broadening.

Improved method for fluorophore deposition atop a polyelectrolyte spacer for quantitative study of distance-dependent plasmon-assisted luminescence

A layer-by-layer deposited polyelectrolyte spacer is used to attach CdSe nanocrystals (NCs), dye molecules and fluorescein-labelled bovine serum albumin (BSA-FITC) to flat glass and rough silver island surfaces in order to study the effect of spacer thickness on homogeneity and surface concentration of fluorophore coverage. Three different methods of fluorophore deposition atop the polyelectrolyte spacer are examined using steady-state spectroscopy, fluorescent microscopy and statistical analysis. The best homogeneous covering with nanocrystals at a controllable concentration was found for deposition from a solution of NCs which are electrostatically bound to polyelectrolyte macromolecules. This fluorophore deposition method allows one to avoid artefacts and to evaluate the fluorescence enhancement factor of BSA-FITC adsorbed on silver island films.

Self-organization of uniform silica globules into the three-dimensional superlattice of artificial opals

Abstract Amorphous spherical silica particles with sizes ranging between 100 and 700 nm, depending on the synthetic conditions and post-preparative treatment, self-organize during slow sedimentation into a 3D solid superlattice of artificial opals where uniform silica globules are closely packed in a face-centered cubic lattice. Sintering of the samples increases their rigidity without affecting the 3D regular structure. Artificial opals exhibit a photonic bandgap—an orientation dependent forbidden frequency gap in the visible spectral range. The photonic bandgap feature makes artificial opals promising candidates for optical applications.

Luminescence in quantum-confined cadmium selenide nanocrystals and nanorods in external electric fields

It is found that the absorption and luminescence spectra of CdSe nanocrystals and nanorods depend on the external electric field. It is shown that the external electric field quenches the P-polarized photoluminescence of CdSe nanorods to a degree higher than the degree of field-induced quenching of the S-polarized photoluminescence. It is established that the nanocrystals are more sensitive to the external electric field than the nanorods. The effect of the external electric field on the luminescence properties of the semiconductor nanorods is discussed.

Colloidal nanophotonics: the emerging technology platform

Dating back to decades or even centuries ago, colloidal nanophotonics during the last ten years rapidly extends towards light emitting devices, lasers, sensors and photonic circuitry to manifest itself as an emerging technology platform rather than an entirely academic research field.