A new class of semiconductors, halide perovskites have stood out from other semiconductors due to their tunable emission properties, ease of fabrication and device integration. Some perovskite nanostructures, e.g. self-assembled hybrid perovskite quantum wells (PQWs) and CsPbX3 nanoparticles, show interesting excitonic properties and enhanced stability towards moisture, oxygen, and heat. In organic semiconductors, triplet excitons are of great importance because they are usually the lowest-energy states and they show long lifetimes and diffusion lengths. However, triplet excitons are dark states. This makes harvesting triplet energy for optoelectronic applications difficult. This thesis focuses on fundamental study on:

1. Understanding the exciton dynamics in two-dimensional PQWs, especially the exciton-phonon coupling dynamics. Femtosecond vibrational spectroscopy was performed to deliver a real-time picture of the phonon modes that interact with excitons. These vibrational modes govern the linewidth broadening and the asymmetric lineshape of the photoluminescence (PL) of PQWs.
2. Triplet energy transfer mechanism from CsPbX3 perovskite nanoparticles to DPA ligands for upconversion purpose. Magnetic field dependent PL (MPL) confirms the triplet-born nature of upconverted emission of DPA, when perovskite nanocrystals were selectively photo excited. The ultrafast (~100 ps) triplet transfer time from perovskite nanocrystals to DPA ligands was determined through transient absorption spectroscopy.
3. The ‘dark’ triplet states of tetracene/TIPS-tetracene were harvested as downconverted emission at the NIR wavelengths using lanthanide materials. Upconverted emission of tetracene/TIPS-tetracene was also observed when lanthanide was selectively excited. MPL and time-resolved spectroscopy were conducted to reveal the transfer mechanisms of this downconversion/upconversion system. These results provide a vital new insight into 2D perovskites and inorganic nanocrystals/organic semiconductor interface and help provide guidelines for material design and engineering.