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.
Highlights
The ever-growing interest and significant progress of carbon-based nanomaterials have witnessed broad prospects in the fields of sensing, catalysis, biomedicine, and optoelectronic devices [1,2,3]
The corresponding results showed that neither of the above cases can produce solid-state white emissive carbon dots (CDs), indicating that both aspartic acid (AA) and ammonia are necessary for the successful preparation of the self-quenching- resistant W-CDs
This indicates that a dehydration reaction must have occurred during the formation process of the W-CDs
Summary
The ever-growing interest and significant progress of carbon-based nanomaterials have witnessed broad prospects in the fields of sensing, catalysis, biomedicine, and optoelectronic devices [1,2,3]. Since the sub-fluorophores did not suffer from direct π-π interactions and were protected by the polymer frameworks, the effective resistance of solid-state quenching could be realized [34] These above strategies satisfactorily solved solid-state PL quenching of CDs, the direct obtained solid-state white emissive CDs are still highly challenging and have very rarely been reported so far [26]. Current commercial white lighting is generally obtained by a combination of blue-emitting InGaN chips and yellow-emitting rare-earth phosphors [36,37,38] Such phosphors are highly efficient light conversion materials, they suffer from expensive resources and high energy consumption during the production process. Based on the superior solid state white emissive feature, the W-CDs were applied to fabricate single-component-based W-LEDs using commercially available UV chips (365 nm) and presented satisfactory performances
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