Tricolor Emitting Carbon Dots from a Single Source Through the Modification of Surface Functional Groups in Ormosil Films
Fabrication of long wavelength emitting Carbon Dots (CDs) with excitation independent nature is a challenging task because of their multifarious applications as successful probes for bioimaging, drug delivery as well as optoelectronics. In this work, a simple strategy has been adopted to fabricate carbon dots (CDs) incorporated organically modified silica (ORMOSIL) films exhibiting tuneable tricolor emission. First, the green emitting CDs with excitation independent nature and high quantum yield (QY) were prepared from o-phenylenediamine (o-PD) in ethanol by solvothermal method. After purification, these green emitting CDs were dispersed in ORMOSIL sol and this CD incorporated ORMOSIL sol emit three intense luminescent colors (orange, yellow and green), under a single ultraviolet-light excitation by adjusting the pH of the pristine sol. It was observed that with pH tuning, the functional groups residing on surface passivated CDs are undergoing chemical modifications and accordingly the PL emission of CDs while incorporated in ORMOSIL sol systematically changes to orange, yellow and green emissions, respectively. Interestingly, these CD-ORMOSIL sols with tricolor emission were utilized to obtain tricolor luminescent films on glass and it was observed that these triluminous nature was well preserved in solid state with substantial concentration. A systematic X-ray photoelectron spectroscopy (XPS) study revealed that the blue shifting in triluminous films (from 560 to 510 nm) with pH increment was originated due to the deprotonation of the surface groups NH2 associated with the CDs. The plausible mechanism behind the rationalization of pH triggered engineering of surface passivated CD-ORMOSIL sols and their confinement in films have been explored.
Keywords - Excitation independent, Tricolor Emission, Carbon Dots, Luminescent, solid state.