Matrix-assisted synthesis of narrow-bandwidth solid-state emissive carbon dots with high PLQY for application in photoluminescence LEDs

Narrow-bandwidth emissive carbon dots (NBE-CDs) can be well applied in light-emitting diodes (LEDs) owing to their excellent properties such as high color purity, high sensitivity, and high photoluminescence quantum yield (PLQY). Currently, most NBE-CDs achieve high PLQY fluorescence emission in solution, whereas NBE-CDs are susceptible to aggregation-caused quenching in solid state, which leads to a sharp decrease or even disappearance of fluorescence intensity. To achieve narrow-bandwidth solid-state emissive of CDs, in this work, a solution of narrow-bandwidth emissive orange CDs (O-CDs) with a full-width at half-maximum (FWHM) of 49 nm and an absolute PLQY of 83.45 % are synthesized through one-step hydrothermal method by using citric acid as carbon source and rhodamine 6G with inherent narrow FWHM as surface modifier. Subsequently, the O-CDs are dispersed in a polyvinylpyrrolidone (PVP) matrix to form O-CDs/PVP fluorescent films, which retains a narrow FWHM of 49 nm and exhibits a PLQY of 59.4 %, thereby enabling solid-state emission. Combining experimental and theoretical simulations, it is found that the solvent environment plays a critical role in determining the FWHM of O-CDs. Specifically, the FWHM gradually decreases as the proton donating capacity gradually weakens and the degree of dispersion deepens. Finally, high-color-purity photoluminescent LEDs with an FWHM of 49 nm are fabricated by combining the O-CDs/PVP fluorescent films with blue LEDs chips. This work provides both theoretical and experimental foundations for the controllable synthesis of efficient narrow-bandwidth solid-state emissive CDs.