Non-radiative recombination pathways in non-carcinogenic quantum dot composites

Owing to their spectrally narrow and high quantum yield photoluminescence, colloidal semiconductor nanocrystals, also known as quantum dots (QDs), are attractive replacements for the broadly emitting white-light phosphors used today that are typically composed of earth-rare elements. Three main factors limit the application of quantum dots as down-conversion phosphors for solid-state lighting: 1) high cost, 2) toxicity, and 3) stability. The high costs of typical quantum dot manufacturing are related to the many manual processing steps that involve expensive raw materials, toxicity is typically due to the presence of cadmium or other carcinogens like indium phosphide, and stability can be very poor without proper design. Quantum dots composed of I-III-VI materials such as CuInS2 offer a compelling alternative to typical semiconductors like CdSe and InP as they have no known toxicity and can be manufactured at a much lower cost. The company proposes to evaluate commercial viability of CuInS2/ZnS QDs for down-conversion in solid-state lighting through the development of composites incorporating them. Ultimately, the company will turn its focus from proof-of- concept to developing large scale manufacturing methods for making the composites. The goals of the initial project are to improve the luminous efficiency of CuInS2/ZnS QDs from about 70% today to >80% both before and after integration into commercial silicones used today in solid-state lighting. This will involve quantitative evaluation and optimization of composite photoluminescence, and stability testing. Spectral tuning and line-width narrowing will not be a priority in Phase I, but brightness and compatibility with silicones will be. Quantum dots are promising as solid-state lighting phosphors (i.e., creating white light from blue LEDs) because the color of their bright luminescence can be tuned by changing their size. This project aims to develop extremely low- cost, efficient phosphors for solid-state lighting using low-toxicity quantum dots. Commercial Applications and Other Benefits: In Phase II, the company will develop spectrally specific and narrow emission composites that are optimized for excitation sources and lighting applications. The company is interested in developing luminescent composites for many other commercial applications in addition to solid-state lighting that will benefit. For example, paints for safety (e.g., stop signs that glow red in headlights), plastics for design (e.g., advertising and consumer products), and solar energy (e.g., luminescent solar concentrators).