Blue and green double band luminescent carbon quantum dots: Synthesis, origin of photoluminescence, and application in white light-emitting devices

Carbon quantum dots (CQDs) have become an excellent candidate for light-converting phosphors. However, it is a challenge to develop white emission CQDs and overcome the agglomeration in the process of solid-state CQDs. Here, white fluorescence CQDs with graphite core structure were synthesized by a one-step hydrothermal method from 1,3-dihydroxynaphthalene and hydrochloric acid. The photoluminescence spectra and surface structure characterization along with UV-Vis absorption spectrum, photoluminescence excitation, and time-resolved photoluminescence spectra together reveal the luminescence of CQDs stems from carbon-oxygen-related surface fluorophores. The principle of solvent similarity compatibility is an effective thought to choose isolating matrix material for the sake of overcoming the agglomeration of CQDs in the process of forming solid film. Solid-state white light emitting device (WLED) was fabricated using the CQDs embedded in polymethyl methacrylate matrix as a single white-light converter excited by a 365 nm UV-LED chip. The fabricated WLED based on CQDs is cold white light source with CIE coordinates (0.3122, 0.3429) and with CCT of 6428 K.