Abstract
Large-scale applications of conventional rare-earth phosphors in white light-emitting diodes (W-LEDs) are restricted by the non-renewable raw material sources and high energy consumption during the production process. Recently, carbon dots (CDs) have been proposed as promising alternatives to rare-earth phosphors and present bright prospects in white lighting. However, the use of CDs in W-LEDs still has two major obstacles, i.e., solid-state quenching and lack of single-component white emissive products. In this work, a facile, rapid, and scalable method for the preparation of solid-state white emissive CDs (W-CDs) is reported via microwave-irradiation heating of L-aspartic acid (AA) in the presence of ammonia. The W-CDs exhibit blue photoluminescence (PL) in dilute aqueous dispersion and their emission spectra gradually broaden (emerging new emissions at orange-yellow regions) with concentration increases. Interestingly, the W-CDs powder displays a very broad PL spectrum covering nearly the whole visible-light region under ultraviolet (UV) excitation, which is responsible for the observed white emission. Further studies revealed that the self-quenching-resistance feature of the W-CDs is probably due to a covering of polymer-like structures on their surface, thus avoiding the close contact of nanoparticles with each other. PL emission of the W-CDs is reasonably ascribed to a cross-linked enhanced effect (CEE) of the sub-fluorophores contained in the material (e.g., -NH2 and C=O). Finally, applications of the W-CDs in fabricating single-component-based W-LEDs using commercially available UV chips were attempted and shown to exhibit satisfactory performances including high white light-emitting purity, high color rendering index (CRI), and tunable correlated color temperature (CCT), thus rendering great promise for W-CDs in the field of white lighting.