Halogen chemistry in the polar boundary layer has received much scientific attention in recent years due to the observations of high concentrations of reactive halogens in springtime. The source of reactive halogens and the site for halogen activation remain a subject of debate. In this thesis, chloride, bromide and sodium ions across the snow-sea ice-seawater interface were measured to study the cryospheric halide distribution and halogen activation in the Arctic. The results show halides/Na+ molar ratios (Br−/Na+ and Cl−/Na+ ratios) in snow are commonly higher than that in seawater, suggesting snow scavenges halides from sources other than sea salt. The decrease in the halides/Na+ ratios in the surface snow layer indicates a loss of halides from the snow, supporting snow as an important substrate for halogen activation. Furthermore, a mechanism for snow-assisted halogen activation is proposed based on the variation of the Br−/Cl− ratio in the snow. / October 2015

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Halide perovskites have attracted the attention of a broad segment of the optoelectronics field, owing to their outstanding optical and electrical properties; simple low-temperature solution processing; low-cost raw materials; and tunable bandgaps. The main objective of this dissertation is engineering the materials’ properties of halide perovskites – their crystallinity, composition, and dimensionality – in order to understand the fundamental photophysical processes leading to their extraordinary behavior and to translate this understanding into optoelectronic applications. This dissertation is divided into two parts: the first focuses primarily on halide perovskites as a photonic source from an emission perspective, whereas the second is devoted to fundamental investigation of emergent photophysical concepts in halide perovskite materials including photon recycling and hot carriers. In the first part of this dissertation, we studied the synthesis and characterization of Cs-Pb-Br-based perovskite-related single crystals to elucidate the origin of the materials’ emission properties. After that, we presented perovskite nanocrystals (NCs) as a color converter in solid state lighting and visible light communication. Perovskites NCs’ converted white light (with a high color rendering index of 89 and a color correlated temperature of 3236 K) exhibits an extraordinary modulation bandwidth of 491 MHz, and data transmission rate of 2 Gbit/s. In the second part of this dissertation, we developed a facile synthesis method for perovskite microwires and demonstrate efficient photon recycling in those microwires with conclusive spectroscopic evidence. Subsequently, we investigated hot charge carriers in halide perovskites solar cells by a combination of laser spectroscopy and density functional modelling. Furthermore, we presented that hot holes were extracted at the device interface between the perovskite absorber and a hole transport layer. The findings and methodologies described in this dissertation represent a significant advance for utilizing the optical properties of halide perovskites, bring new fundamental photophysical insights to the field of halide perovskites, and provide a new powerful approach for designing the interface of perovskite solar cells to efficiently extract the hot charge carriers.