Optical seminar | 29 January 2021

To date perovskite nanostructured materials are widely applied in optics and electronics due to their excellent photophysical properties, such as narrow full width at half maximum (FWHM), high photoluminescence quantum yield (PLQY), tunable emission spectra etc. There are a number of reports dedicated to the fabrication of optoelectronic devices based on perovskite materials, e.g., light-emitting diodes (LEDs), scintillators, lasers, solar cells. Similarly to the linear optical properties of perovskite nanocrystals (NCs) under ultraviolet (UV) or visible light excitation, their nonlinear optical properties such as near-infrared (NIR)-triggered photon upconversion can be potentially applied for in vivo bioimaging due to an increased penetration depth of NIR light. However, instability of perovskites in aqueous solutions (biological fluids, water and others) is a huge barrier that prevents their utilization in biomedical applications.This study is aimed at the development of optimized conditions for the obtaining of lead halide perovskite (CsPbBr3) NCs coated with a silica shell exhibiting improved stability in water. For this, tetramethyl orthosilicate (TMOS) and triethoxyphenylsilane (phTEOS), which contains hydrophobic phenyl group, are added in various ratios (in total 7 ratios) to a modified ligand assisted reprecipitation (LARP) perovskite NC synthesis approach. Hydrolysis-condensation reaction of TMOS and phTEOS result in a highly branched three-dimensional silica structure (siloxane network). Addition of phTEOS to the synthesis increases the hydrophobicity of the resulting SiO2 shell that can induce stability of perovskites in aqueous solutions. Consequently, perovskite NCs coated with silica shells of various compositions (in total 7 samples) are obtained. High quality of the CsPbBr3 NCs coated with SiO2 shell (CsPbBr3@SiO2 NCs) is confirmed with high-resolution transmission and scanning transmission electron microscopy (HRTEM and STEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) and energy-dispersive X-ray (EDX) spectroscopies, as well as fluorescence optical microscopy. The stability of the obtained products is probed in water during 24 h. We reveal strong dependence between the shell composition (added TMOS:phTEOS ratio during synthesis) and the water-resistance of CsPbBr3@SiO2 NCs as verified with photoluminescence (PL) measurements at different time points. The resulting CsPbBr3@SiO2 NCs possess upconversion properties. As a proof of concept, the obtained CsPbBr3@SiO2 NCs with the highest stability in water are utilized in vitro experiments with human mesenchymal stromal cells (hMSCs) and murine melanoma cell line (B16-F10 cells). We demonstrate decreased cytotoxicity of CsPbBr3@SiO2 NCs at the concentrations added and the possibility of NC-cell association. Additionally, we show that superb optical properties of CsPbBr3 can be realized for upconversion in a living cell.

The acceleration of radiative recombination channel can be extremely useful in optoelectronic devices based on halide perovskites, where high external quantum yield of emission is beneficial both for light-emitting devices and solar cells. In this talk, I will present the results of my PhD study witch devoted to the research of radiative recombination in the structures based on lead halide perovskite.

The research is devoted to the study of the metamaterial regime in the quasicrystal structure. As an example, we consider the quasicrystal structure of dielectric rods arranged at the vertices of rhombs which forming the Penrose tiling.