Direct blending of multicolor carbon quantum dots into fluorescent films for white light emitting diodes with an adjustable correlated color temperature

White light-emitting diodes (WLEDs) with a high color rendering index (CRI) and an adjustable correlated color temperature (CCT) are of great importance in a wide range of fields. We report an efficient method to fabricate WLEDs with prominent CCT performance by the combination of multi-colour carbon quantum dots (CQDs). Long-wavelength CQDs with green, yellow and orange emission (denoted as G-, Y-, and O-CQDs, respectively) were obtained by a one-pot solvothermal reaction between phthalic acid and o-phenylenediamine followed by precise separation by silica column chromatography. Systematic investigation and detailed characterization demonstrate that G- and Y-CQDs emit mainly due to the quantum size effect, while the photoluminescence emission of O-CQDs is mainly derived from surface defect states formed by surface oxidation. Subsequently, solid-state luminous red-green-blue CQD films obtained by using tri-functional blue emitting CQDs (phosphors, dispersants and curing agents) lead to UV-pumped WLEDs with good color stability and a high CRI (83–88) as well as an adjustable CCT (3466–7368 K). This work has opened up new avenues for the development of low-cost, environmentally-friendly and high-performance CQD phosphor-based WLEDs.