Excitons are evanescent quasiparticles which serve as transient reservoirs for electronic and photonic energy in many critical processes, including photosynthesis, photovoltaics, electroluminescence and photocatalysis. Efficient use of excitonic processes ultimately relies on precise control of exciton dynamics, namely, the ability to manage the transportation, conversion and release of the exciton energy. These operations require a thorough understanding of mechanisms that govern the exciton dynamics. Our research focuses on designing nanostructures with semiconductor quantum dots based on systematic investigations into fundamental science using state-of-the-art optical spectroscopies. We develop pump-probe techniques for time-resolved electronic and vibrational spectroscopy and microscopy, in order to understand and eventually utilize exciton energy in nanostructures and organic/inorganic hybrid composited nanomaterials. The applications that will implement in our lab including controlling non-radiative exciton decay processes for directly converting light into mechanical energy, developing photo-switchable sensors emitting in the near-IR window for biological imaging, and manipulating charge carrier dynamics in nanostructures to improve the efficiency of photocatalytic reactions.

Exciton: The crossroad of Energy Conversion

Among excitonic materials, colloidal semiconductor nanocrystals (generally known as quantum dots (QDs)) are unique because (i) the quantum confinement effect enables tunable optical transitions depending on their physical dimensions, and (ii) the nature of QD excitons can be manipulated using their surface chemistry. These properties have made QDs promising materials for a broad range of applications from solar energy conversion and optoelectronics to sensing and biological imaging.

Semiconductor Quantum dots

Picture from  internet resources

The overarching goal of our research is to realize the fine control of the radiative and non-radiative decay processes in nanoparticles in order to efficiently utilize the photo-generated excitons and charge carriers for desired applications. We think to implement the idea on various platforms, including but not limited to (I) inorganic QD organic semiconductor composite for novel optoelectronic applications, (II) QD nanomotors that can convert photon energy to mechanical energy through regulated nonradiative energy dissipation, (III) photoswitchable near-infrared emitters controlled by photochromic compounds for biological imaging, and (IV) photocatalytic redox reactions powered by mediated charge carriers in nanoparticle heterojunctions.

Nanomotors: Regulation of Energy Dissipation
Photo-switchable sensors
Photocatalytic Clusters

For rational design of materials with controllable exciton behaviours, it is critical to understand the relationship between functional structures and exciton dynamics. We implement various optical spectroscopic tools that can monitor the evolution of excitonic states by probing both the electronic transitions (e.g. transient absorption, and time-resolved photoluminescence) and vibrational signals (e.g. Raman) to analyze the dynamics of carriers in different systems.

Time-resolved Laser Spectroscopy for Monitoring Exciton Kinetics and Vibrational Structures