MID-INFRARED COLLOIDAL QUANTUM DOTS LEDs

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The objective of the project is to explore mid-infrared colloidal inorganic Quantum dot Light Emitting Diodes (QLEDs). For visible light, QLEDs are widely investigated as a competition to organic LEDs. The solution processing allows such high volume and area production that either approaches, inorganic quantum dots or molecular dyes, are revolutionizing the display and lighting technologies. This project differs in aiming to take advantage of the specifically inorganic nature of colloidal quantum dots which allows in principle infrared luminescence, and to start research on mid-infrared QLEDs. The applications will mostly derive from the fact that the mid-infrared covers the molecular fingerprint region. As such, a combination of inorganic quantum dot LEDs and detectors, both made by simple solution processing and printing, could revolutionize molecular sensing. Example of applications could be sensing of toxic or greenhouse gases as well as fat or protein content in the food industry. The project therefore aims to start the exploration of mid-infrared inorganic quantum dot LEDs, it includes the synthesis of novel bright mid-infrared semiconductor quantum dots and their incorporation into novel mid-infrared light emitting diodes. The emission efficiency of LED scales proportionally to the photoluminescence efficiency of electron-hole recombination, along with other losses due to poor photon extraction, Auger effects and leakage current. In principle, inorganic quantum dots should be efficient mid-IR chromophores, because they have low phonon frequencies and low electronic density of states. Yet, to date, the record efficiency for a colloidal quantum dot emitting at 5 microns is only 2%. It is thought that this is not yet limited by multiphonon processes but instead related to surface and vibrational absorption from surface or matrix The project will therefore pursue material synthetic approaches to increase the brightness. In parallel, these new chromophores will be incorporated into a mid-IR LED by developing new approaches and borrowing strategies developed for visible QLEDs and the more conventional mid-infrared III-V epitaxial semiconductor based mid-infrared LEDs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.