High-Performance Carbon Quantum Dots for Warm WLEDs

by | Sep 18, 2017

Highly efficient, red-emissive carbon quantum dots (R-CQDs) with a quantum yield of 53% are prepared and a CQD-phosphors-based warm white-light-emitting diode (WLED) is realized for the first time.

Modern civilization depends on electric lighting to power homes, offices, roads, and industry. The right lighting can help us to navigate, stimulate and excite our senses, or create a calm, relaxing atmosphere. White-light-emitting diodes (WLEDs) are attractive due to their long operating lives and energy-saving abilities, and their natural color rendering is desirable for comfortable ambient lighting.

In Advanced Materials, Louzhen Fan, Shihe Yang, and co-workers from Beijing Normal University, Beijing Institute of Technology, and the Hong Kong University of Science and Technology synthesize highly efficient, red-emissive carbon quantum dots (R-CQDs) with a high quantum yield (QY) of 53% and a high color rendering index (CRI) of 97, which they use for ultraviolet (UV)-pumped, warm WLEDs based on tricolor CQDs: blue, green, and red.

The researchers synthesize the uniform-size (≈5 nm), highly crystalline R-CQDs using a dehydrative condensation and dehydrogenative planarization method followed by column chromatography. Under UV light in ethanol, these R-CQDs fluoresce bright red.

They then prepare red/green/blue tricolor CQD phosphors by dispersing the R-CQDs with their previously synthesized blue (B)-CQDs and green (G)-CQDs in a highly transparent polymer matrix of polyvinylpyrrolidone. The resulting photoluminescence spectra cover the full visible range and performance remains stable at temperatures up to 150 °C. A warm WLED lamp is then fabricated using a 370 nm UV LED chip as the excitation source, covered with silicone-dispersed B-, G-, and R-CQD phosphors. Compared to a commercial WLED lamp, their warm WLED lamp shows a truer color match.

To find out more about this high-color-accuracy, warm WLED, please visit the Advanced Materials homepage.

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