Light-emitting diodes (LEDs) offer great prospects for developing low-cost, efficient, bright, and large area color displays and white-light lighting. Traditional LEDs use rare earth or organic luminescent materials. Quantum dots (QDs) based LEDs (QD-LEDs) exhibit size tunable spectral emission, allowing for the design and fabrication of color QD-LEDs with simple device configurations for individual pixel based color elements. However, a serious drawback of the present colloidal QD-LED technology is its dependence on the QDs with toxic heavy-metal components, such as cadmium, lead, and mercury which are detrimental to the environment and therefore potentially hinder the commercialization. Carbon nanoparticles (also called carbon dots, abbreviated as CDs) are recently developed new materials. They are easy to make from simple raw materials. Carbon is the earth abundant material, safe, biocompatible, and cheap. CDs also show different colors under light excitation (photoluminescence) with very high quantum yields. The inventors developed CD-based LEDs (CD-LEDs) for color display (e.g., computer monitors, TVs, phone screens, entertainment lighting, instrument back lighting) and white-light solid-state lighting (for buildings, rooms, personal reading/study, public areas, roads, etc.).
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