Solid-state red emissive carbon dots based on high boiling point solvents for white light-emitting diodes

A simple and rapid one-step microwave-assisted method was employed to synthesize solid-state red emissive carbon dots (R-CDs) using phloroglucinol, urea, and ammonium fluoride in a high-boiling point solvent. Raw material ratios and solvent types were investigated. The optimal emission of R-CDs at 625 nm was achieved when the molar ratio was 3:1:6 in a 50% N, N-dimethyl formamide/water for 15 min. When formamide and water (v/v = 5:95) were used, R-CDs with longer emission (640 nm) were obtained and the reaction time was shortened to 3 min, enhancing both efficiency and cost-effectiveness. Both R-CDs maintained >96% fluorescence intensity after UV exposure and <5% weight loss at 200°C. Combined with polyvinyl pyrrolidone, R-CDs baesed red LEDs with CIE coordinates (0.67, 0.33) and (0.62, 0.38) were achieved. Combined with blue/green CDs, white LEDs showed color rendering indexes of 91-92. This study advances solid-state red CDs for high-quality white LEDs.