Deprotonation-Induced Excitation-Independent PL Emissions in Red-Emissive Carbon Dots

Abstract

Red-emitting carbon dots (r-CDs) are among the most challenging categories of carbon-based luminescent materials to synthesize with high emission color purity, photoluminescent quantum yield, and photostability. While r-CDs are used as red phosphors in white LEDs to compensate for spectral deficiencies caused by strong blue and green emissions, their emission mechanisms warrant further investigation. Herein, we synthesized r-CDs via a facile, one-step, environmentally benign solvothermal method. We analyzed the structure of our r-CDs using Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier infrared spectrometry (FTIR). Subsequently, the optical properties were investigated using a UV-Vis spectrophotometer and spectrofluorometer. The TEM image showed well-dispersed quasi-spherical dots with an average diameter of 3.47 nm. The photophysical investigation revealed that the r-CDs exhibit excitation-dependent emissions from 400 to 750 nm in water, whereas in DMSO, the emission spectra are excitation-independent, with a peak centered at 680 nm. The excitation-independent spectra observed were attributed to DMSO-induced deprotonation of surface functional groups on r-CDs, resulting in solvent-induced red emission and a high photoluminescent quantum yield (PLQY) of 31.3%.