Dyakonov surface waves in a thin interfacial waveguide formed by negatively anisotropic dielectrics.

Dyakonov surface waves (DSWs) are electromagnetic surface waves that exist at the interface of two dissimilar materials, with at least one material being anisotropic. Although there are various types of these waves, they all exist in anisotropic materials with positive anisotropy. The requirement for positive anisotropy limits the choice of materials that can support these waves. In this study, we present a type of Dyakonov surface wave that occurs at the interface of negatively anisotropic materials. Specifically, we demonstrate their existence in a system consisting of two negatively anisotropic slabs confined between two perfect electric conductor (PEC) walls. By assuming a small distance between the walls, we derive analytical expressions for the propagation constant, penetration depth, and field distribution of these surface waves. We numerically demonstrate that these surface waves can also exist in structures beyond the approximations used to develop the theoretical framework. The existence of Dyakonov surface waves in negative crystals broadens the range of materials suitable for their practical implementation.

Nearly perfect near-infrared luminescence efficiency of Si nanocrystals: A comprehensive quantum yield study employing the Purcell effect.

Thin layers of silicon nanocrystals (SiNC) in oxide matrix with optimized parameters are fabricated by the plasma-enhanced chemical vapor deposition. These materials with SiNC sizes of about 4.5 nm and the SiO2 barrier thickness of 3 nm reveal external quantum yield (QY) close to 50% which is near to the best chemically synthetized colloidal SiNC. Internal QY is determined using the Purcell effect, i.e. modifying radiative decay rate by the proximity of a high index medium in a special wedge-shape sample. For the first time we performed these experiments at variable temperatures. The complete optical characterization and knowledge of both internal and external QY allow to estimate the spectral distribution of the dark and bright NC populations within the SiNC ensemble. We show that SiNCs emitting at around 1.2-1.3 eV are mostly bright with internal QY reaching 80% at room temperature and being reduced by thermally activated non-radiative processes (below 100 K internal QY approaches 100%). The mechanisms of non-radiative decay are discussed based on their temperature dependence.

Plasmon induced modification of silicon nanocrystals photoluminescence in presence of gold nanostripes.

We report on the results of theoretical and experimental studies of photoluminescense of silicon nanocrystals in the proximity to plasmonic modes of different types. In the studied samples, the type of plasmonic mode is determined by the filling ratio of a one-dimensional array of gold stripes which covers the thin film with silicon nanocrystals on a quartz substrate. We analyze the extinction, photoluminesce spectra and decay kinetics of silicon nanocrystals and show that the incident and emitted light is coupled to the corresponding plasmonic mode. We demonstrate the modification of the extinction and photoluminesce spectra under the transition from wide to narrow gold stripes. The experimental extinction and photoluminescense spectra are in good agreement with theoretical calculations performed by the rigorous coupled wave analysis. We study the contribution of individual silicon nanocrystals to the overall photoluminescense intensity, depending on their spacial position inside the structure.