Colloidal nanocrystals are nanometer sized inorganic crystals synthesized and manipulated in solution. Their size dependent properties render great potential for colloidal nanocrystals to be outstanding candidates as novel and high performance materials. Fundamentally, matters in nanometer size regime are much less explored in history of human being, and thus they represent frontiers of today’s science.

Though we don’t limit ourselves to any given sub-class of colloidal nanocrystals, semiconductor nanocrystals (quantum dots, QDs) are the main focus area at present.

Our general philosophy is to combine fundamental research with materials function. Specifically, we usually select most promising material systems as our model systems of fundamental studies. Given the extremely rapid depletion of nature resources, such philosophy should promote development of basic sciences of novel and high performance materials that are much needed for the foreseeable future of human society.

Synthetic chemistry of colloidal nanocrystals and mechanisms of crystallization

Quality of colloidal nanocyrstals is the first step for realization of any desired function and understanding of any fundamental principle of colloidal nanocrystals. This is why the Peng’s group has chosen synthetic chemistry of colloidal nanocrystals as its main mission. The main challenge on development of synthetic chemistry of colloidal nanocrystals lies on lacking of adequate theoretical framework of crystallization. Combination of synthetic development with investigation of crystallization is a natural style of research along this direction.

Semiconductor nanocrystals are probably the most promising class of emissive materials for optoelectronics, bio-medical imaging, and sensing. Though control of size and size distribution has achieved to a much advanced level in the past twenty years or so, control on their optical properties to monodisperse level remains as a challenge. Our current emphasis of synthetic chemistry of semiconductor nanocrystals is to initiate such efforts in the field.

Spectroscopy and optical materials

Quantum dots as luminescence nano-materials have already been applicable in a number of applications. However, there is still a great gap between real life applications and their promises. Lacking of fundamental understanding of their spectroscopic properties is one limiting factor, in addition to their synthetic control. Spectroscopy studies of the Peng’s group have two main themes. The first main theme is to assist synthetic chemistry development, especially synthetic control of the excited properties of colloidal nanocrystals. The second theme is to discover novel and high performance optical materials for various applications.

Besides routine spectroscopic methods such as absorption and steady-state photoluminescence spectroscopies, we study optical properties of nanocrystals mainly based on two advanced techniques. One is transient-state spectroscopy for studying excited state dynamics in nanocrystal systems. The other one is single-molecular spectroscopy.

Applications and related chemistry/physics

Size dependent properties and solution-based processibility of colloidal nanocrystals are exploited for a variety of applications, such as optoelectronics, bio-medical imaging, catalysis, etc. Research along this direction in the Peng’s group aims at those cutting-edge applications that shall likely make immediate impact to industry. The aiming angle emphasizes processing chemistry of colloidal nanocrystals associated with specific devices.

The current emphasis of optoelectronic devices is high performance light-emitting-diodes based on quantum dots. In collaboration with our partners in academic and industrial sectors, the goal is to advance the technology to real life products for solid-state-lighting and displays. Another example of applications is bio-medical imaging using nanocrystals.