One-Step Synthesis of Amine-Functionalized White-Light-Emitting Carbon Dots and Temperature-Dependent Photoluminescence Studies

We synthesized amine-functionalized, white-light-emitting (WLE) carbon quantum dots using amino acid l-3,4-dihydroxyphenylalanine (DOPA) as a carbon precursor via a one-step, slow, low-temperature oxidative pyrolysis reaction. The synthesized carbon dots (DP-CD) were well-characterized by different spectral techniques, including XRD, XPS, FTIR, contact angle measurement, and steady-state and time-resolved fluorescence spectroscopic techniques. This single precursor containing carbon, nitrogen, and oxygen ensures nitrogen doping in the frameworks and is also responsible for different functional groups, such as amine, carboxyl, and amide, on the surface. An excitation-wavelength-dependent emission, along with intense white-light emission under UV excitation in the solution and thin film state, makes these materials single-component WLE phosphors. The origin of white-light emission is understandably the simultaneous emission from multiple chromophoric species in the carbon dots (CDs) covering the entire visible spectral region. The excitation-resolved area-normalized spectra (ERANES) and time-resolved area-normalized spectra (TRANES) exhibit isoemissive points ascertaining the presence of multiple chromophoric species. The surface amino groups on the DP-CD are essential to maintain the fluorescence properties because their reaction with aldehydes leads to diminished fluorescence quantum yields. The temperature-dependent fluorescence spectra exhibit a linear relationship between the temperature and emission intensity at longer excitation wavelengths and could make them candidates for luminescent temperature sensor applications.