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Results obtained in an experimental study of spontaneous emission from erbium ions in a spectral range corresponding to the lower photonic band edge of distributed Bragg reflectors (1D photonic crystals) are presented. The photonic crystals were constituted of alternating quarter-wave a-Si:H and a-SiOx:H layers grown by PECVD. Erbium was introduced into the a-Si:H layers by magnetron sputtering of an erbium target in the course of structure growth. The change observed in the intensity of spontaneous emission is due to the nonmonotonic behavior of the density of optical modes near the photonic band edge. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

VO[sub 2] photonic crystals exhibiting a semiconductor-metal phase transition at 55-75°C have been synthesized by the infiltration of vanadium dioxide (VO[sub 2]) into opal crystals and the subsequent removal of SiO[sub 2] 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 VO[sub 2] 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. [ABSTRACT FROM AUTHOR]

Three-dimensional opal-silicon composites both with a direct (with different extent of the opal voids filling with Si) and inverted structure were synthesized, and their structural analysis was carried out. The spectra of specular reflection from (111) growth surfaces of the synthesized composites were measured in the wavelength range from 400 to 900 nm. The features observed in the spectra are analyzed theoretically and interpreted as manifestations of the photonic band gap in the direction [111]; the band gap position and width can be tuned in the visible and near-infrared spectral range. [ABSTRACT FROM AUTHOR]

We demonstrate spectral shifting of the photonic band gap in a three-dimensional photonic crystal within a time of less than 350 fs. Single 120 fs high-power optical pulses are capable to induce the transition from the semiconductor to the metallic phase of VO2 in the pores of our artificial silica opal. The phase transition produces a substantial decrease of the real part of the effective refractive index of the photonic crystal and shifts the spectral position of the photonic band gap. [ABSTRACT FROM AUTHOR]

Three-dimensional opal–VO2 photonic crystals were prepared by the chemical bath deposition technique. The x-ray diffraction and Raman spectroscopic data confirm the crystalline perfection of VO[sub 2] impregnated into synthetic opal pores. It is shown from the optical reflectivity measurements that the photonic bandgap of the opal–VO2 composite is governed by the phase transition in VO2. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A modified plasma-enhanced chemical vapor deposition technology is developed for nanocrystalline Si which combines the standard rf glow discharge method and the hollowcathode discharge method in a single process cycle. The volume fraction of nanocrystallites varied monotonically along the layer, whereas their size remained constant. The electrical and optical characteristics of these films were investigated. [ABSTRACT FROM AUTHOR]

Ultrafast (30 fs) all-optical switching of the reflectivity in an opal–Si three-dimensional photonic crystal is demonstrated in the visible and the near-infrared spectral range. Photoinduced changes turn out to be enhanced around the photonic stop bands and reach 46% at high excitation power. We show that the switching time is as short as 30 fs and is determined by the pump–pulse duration. [Copyright &y& Elsevier]

We demonstrate ultrafast all-optical switching in a three-dimensional photonic crystal made of an opal-silicon composite. We show that the switching-on time is faster than 30 fs and determined by the pump pulse duration. The switching-off time is in the order of several picoseconds. The maximum transient change in reflectivity reaches values as high as 46% at the highest excitation power. [Copyright &y& Elsevier]