Gram-Scale Synthesis of Highly Efficient Rare-Earth Element-Free Red/Green/Blue Solid-State Bandgap Fluorescent Carbon Quantum Rings for White Light-Emitting Diodes.

Abstract

Rare-earth element (REE)-based materials are commonly used in phosphor-converted white light-emitting diodes (LEDs). However, the negative impact of their use on the environment, human health, supply risks, and high cost prompts the need for REE-free materials. Here, we report the gram-scale synthesis of red/green/blue solid-state bandgap fluorescent carbon quantum rings (R/G/B-SBF-CQRs) with high quantum yields\xa0up to\xa030-46%. This was achieved using cyano-group-bearing p-phenyldiacetonitrile and aldehyde-group-bearing terephthalaldehyde as precursors and forming carbon quantum rings of different diameters through the linkage of curved carbon quantum ribbons of different lengths. The results show the role of cyano groups in the curvature of carbon quantum ribbons for CQR formation and emission of stable solid-state bandgap fluorescence. R/G/B-SBF-CQR-phosphor-based LEDs emitted warm white light with low correlated color temperature (3576 K), high color rendering index (96.6), and high luminous efficiency (48.7 lm W -1 ), comparable to REE-phosphor-based LEDs. This work facilitates the development of high-performance low-cost REE-free phosphors.