Single-component white-light-emitting carbon quantum dots from lignite coal with adaptive broad colour-temperature tunability.

Sustainable single-component white light emitters exhibiting tunable correlated colour temperature (CCT) while maintaining a nearly constant colour rendering index (CRI) (>75) are very scarce in the literature. In this connection, single-component white-emitting carbon quantum dots (CQDs) were synthesized from Indian lignite coal via a simple one-step dimethyl sulfoxide (DMSO)-assisted ultrasonication process at room temperature. The resulting 4.0 nm average-sized CQDs exhibited a broadband emission profile from 400-750 nm across the entire visible spectrum under 390 nm excitation. Remarkably, the CCT can be tuned over a wide range from near warm-white (4535 K) to daylight-white (11 258 K), simply by varying the amount of lignite precursor from 0.03 to 0.08 g, while maintaining the CRI within 74-80. The optimized CQDs displayed chromaticity coordinates of (0.27, 0.34), a CCT of 8612 K, and a CRI of 76. Furthermore, flexible CQD-mixed with polyvinyl alcohol (PVA) composite films and CQD-coated light-emitting diode (LED) chips were fabricated, demonstrating their practical utility in solid-state white-light-emitting devices. To the best of our knowledge, this is the first report of lignite-derived single-component white-emitting CQDs exhibiting controllable broad CCT tunability through simple precursor-mass modulation while preserving acceptable colour-rendering performance.