Semiconductor nanocrystals (quantum dots, QDs) represent a milestone in the field of luminescent nanoparticles owing to their unique optical properties. Silica encapsulation of colloidal QDs in optimized synthetic conditions provides an excellent method to reduce their cytotoxicity maintaining, at the same time, their optical properties.1 The ability to optically confine and spatially control these biocompatible nanostructures in liquid media boosts their investigation for bioimaging both as an ensemble as well as at a single particle-level.
In this study we explore the optical trapping of silica-encapsulated QDs in a near infrared counter-propagating experimental configuration.2 Optically trapped QDs exhibit two photon-absorption mediated luminescence without additional excitation sources.3,4 We find that the luminescence, collected through one objective, evidences photo-bleaching and wavelength blue-shifts depending on the dispersive medium composition and power density in the laser focus.
In this paper the fabrication of photonic slab heterostructures based on artificial opals is presented. The innovated method combines high-quality thin-films growing of opals and silica infiltration by Chemical Vapor Deposition through a multi-step process. By varying structure parameters, such as lattice constant, sample thickness or refractive index, different heterostructures have been obtained. The optical study of these systems, carried out by reflectance and transmittance measurements, shows that the prepared samples are of high quality further confirmed by Scanning Electron Microscopy micrographs. The proposed novel method for sample preparation allows a high control of the involved structure parameters, giving the possibility of tunning their photonic behavior. Special attention in the optical response of these materials has been addressed to the study of planar defects embedded in opals, due to their importance in different photonic fields and future technological applications. Reflectance and transmission measurements show a sharp resonance due to localized states associated with the presence of planar defects. A detailed study of the defect mode position and its dependance on defect thickness and on the surrounding photonic crystal is presented as well as evidence showing the scalability of the problem. Finally, it is also concluded that the proposed method is cheap and versatile allowing the preparation of opal-based complex structures.
An optical and morphological study has been carried out to understand the role of intrinsic defects in opal-based photonic crystals. The inherent polydispersity in sphere size distribution yields imperfect crystallizations and worsens the photonic properties of these systems. By doping poly-(mehtymethacrylate) thin films opals with polystyrene spheres of larger size it is possible to study the disorder caused by the dopants and the negative influence in the optical response. In addition, it is feasible to grow mixed structures (alloys) with intermediate photonic properties by mixing spheres of different nature and the same size.