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Encapsulating Cs4PbBr6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs4PbBr6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs4PbBr6 pseudo-spherical quantum dots is quenched and is dominated with Pb2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs4PbBr6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs4PbBr6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials. 

Silicon nanotubes (Si NTs) have a unique structure among the silicon nanostructure family, which is useful for diverse applications ranging from therapeutics to lithium storage/recycling. Their well-defined structure and high surface area make them ideal for sensing applications. In this work, we demonstrate the formation of Au nanoparticles (NPs) functionalized with 4-Mercaptophenylboronic acid (MPBA) on porous Si NTs (pSi NTs) fabricated using ZnO nanowires as a template. The system was characterized, and the proposed structure was confirmed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Varying glucose concentrations in phosphate-buffered saline (PBS) (0.5–80 mM) were introduced to the Si NT nanocomposite system. The glucose is detectable at low concentrations utilizing surface-enhanced Raman spectroscopy (SERS), which shows a concentration-dependent peak shift in the benzene ring breathing mode (~1071 cm−1) of MPBA. Complementing these measurements are simulations of the Raman hot spots associated with plasmonic enhancement of the Au NPs using COMSOL. This biocompatible system is envisioned to have applications in nanomedicine and microfluidic devices for real-time, non-invasive glucose sensing. 

Twisted photonic crystals are photonic analogs of twisted monolayer materials such as graphene and their optical property studies are still in their infancy. This paper reports optical properties of twisted single-layer 2D+ moiré photonic crystals where there is a weak modulation in z direction, and bilayer moiré-overlapping-moiré photonic crystals. In weak-coupling bilayer moiré-overlapping-moiré photonic crystals, the light source is less localized with an increasing twist angle, similar to the results reported by the Harvard research group in References 37 and 38 on twisted bilayer photonic crystals, although there is a gradient pattern in the former case. In a strong-coupling case, however, the light source is tightly localized in AA-stacked region in bilayer PhCs with a large twist angle. For single-layer 2D+ moiré photonic crystals, the light source in Ex polarization can be localized and forms resonance modes when the single-layer 2D+ moiré photonic crystal is integrated on a glass substrate. This study leads to a potential application of 2D+ moiré photonic crystal in future on-chip optoelectronic integration.