A. V. Sel’kin

Hysteresis of the photonic band gap in VO2 photonic crystal in the semiconductor-metal phase transition

VO2 photonic crystals exhibiting a semiconductor-metal phase transition at 55–75°C have been synthesized by the infiltration of vanadium dioxide (VO2) into opal crystals and the subsequent removal of SiO2 by etching. A study of the optical reflection spectra of such crystals demonstrated that they are characterized by a wide photonic band gap (in the [111] direction of light propagation) in the visible spectral range. The energy position of this band gap changes abruptly upon a phase transition. The temperature shift and hysteresis of the position of the photonic band gap were measured. Quantitative calculations of the reflection spectra of photonic crystals of opal and VO2 were performed in terms of the model of a layered periodic medium, and numerical values of the geometric parameters and optical constants of the studied three-dimensional periodic structures were obtained.

Polarization-dependent suppression of Bragg reflections in light reflection from photonic crystals

This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ϑc, at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ϑc, which depends on the geometric parameters and dielectric constants of the spatially periodic structure.

Splitting of resonant optical modes in Fabry-Perot microcavities

Splitting of resonant optical modes in Fabry-Perot microcavities with distributed Bragg reflectors is studied experimentally. The splitting was detected in polarized light at large angles of incidence onto the external boundary of a microcavity. A theoretical model is developed which makes it possible to describe quantitatively all of the special features of the splitting observed.

Fabry-Perot a-Si:H/a-SiOx:H microcavities with an erbium-doped a-Si:H active layer

Fabry-Perot microcavities tuned to a wavelength of 1.5 µm have been fabricated by means of plasma-enhanced chemical-vapor deposition on the basis of a-Si:H and a-SiOx:H. Distributed Bragg reflectors (DBRs) and the active layer were grown in a single technological cycle. The half-wave active layer was doped with erbium in the course of growth from a metal-organic compound. The high optical contrast enabled a high microcavity quality factor (Q=355) with only three DBR periods. The intensity of erbium photoluminescence (PL) from the microcavity is two orders of magnitude higher than that of erbium emission from an identical a-Si:H layer without DBR. Transmission, reflection, and PL spectra are analyzed. It is found that the spectral shape of the line of erbium PL (transition 4I13/2 → 4I15/2) from the microcavity virtually coincides with the shape of the resonance peak of its transmission spectrum. Theoretical calculations have been performed providing a comprehensive description of the observed experimental spectra.

Emulsifier-free emulsion copolymerization of styrene with methacrylic acid as a method of preparing building blocks for photonic crystals

Monodisperse polymer particles with diameters from 230 to 420 nm have been synthesized by the emulsifier-free emulsion copolymerization of styrene with methacrylic acid. It has been shown that an initiator, chain regulators, comonomer ratio, and pH of a medium influence the dispersity of latexes, the distribution of carboxyl groups in polymer particles, as well as their swelling behavior and electrophoretic mobility. These characteristics of polymer particles are substantial for designing perfect lattices of three-dimensional photonic crystals on their basis.

Optical spectroscopy of near-surface excitonic states

Abstract We have studied the low temperature excitonic reflectance and luminescence spectra of CdS 1− x Se x solid solutions with a near-surface excitonic potential well formed by excessive Se. The reflectance spectra were obtained at different angles of incidence for both s - and p -polarization components of light. New striking spectral features due to exciton confinement and quantization in the surface region were observed. For various samples, the generalized Morse surface potential was proved to be a good approximation in describing the experimental data. It is shown that the resonance excitonic luminescence is largely governed by the emission from excitations localized in the well.

Optical characterization of natural and synthetic opals by Bragg reflection spectroscopy

The Bragg reflection of light from natural and synthetic opals was studied experimentally, and the samples were characterized by atomic-force microscopy. The reflection spectra were theoretically calculated within the model of a planar, periodically layered medium. A comparison of the experimental and calculated data made it possible to determine the parameters of the crystal structure of synthetic opals (lattice constants and sintering coefficients of a-SiO2 particles). It was concluded that the pores in the structure of natural opals are filled by a material with a refractive index close to that of a-SiO2.

Fabrication and Optical Properties of Photonic Crystals Based on Opal-GaP and Opal-GaPN Composites

Nanocrystalline GaP and amorphous GaPN solid solution have been synthesized in voids of artificial opal. The opal-GaP and opal-GaPN composites obtained clearly demonstrate properties of photonic crystals. The reflection spectra of the opal-GaPN composite exhibit specific features related to multiple Bragg diffraction on two systems of {111} planes, parallel and nonparallel to the surface of the photonic crystal. The study of photoluminescence spectra revealed a considerable modification of the emission band of the opal-GaPN composite, which was attributed to the influence of the photonic band gap.

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO2-based structure has been analyzed.

Luminophore-containing polymer particles: Synthesis and optical properties of thin films on their basis

For the synthesis of monodisperse submicron particles (in which a luminophore is covalently bound to the polymer matrix), methods of emulsifier-free emulsion and seeded copolymerizations are applied to introduce the luminophore-containing monomer into the bulk or shell of the particles, respectively. Scanning electron microscopy and optical spectroscopy (reflection and luminescence spectra) showed that the particles obtained by the first method are better able to self-assemble into 3D-ordered thin-film structures displaying photonic crystalline properties.