Carbon Dots from a Single Source Exhibiting Tunable Luminescent Colors through the Modification of Surface Functional Groups in ORMOSIL Films

A simple strategy to fabricate carbon dots (CDs) incorporated organically modified silica (ORMOSIL) films exhibiting tunable tricolor emission has been accomplished. First, the green-emitting CDs with excitation-independent nature and high quantum yield were prepared from <i>o</i>-phenylenediamine in ethanol by solvothermal method. These CDs after purification were dispersed in ORMOSIL sol, and their photoluminescence wavelengths were tuned to three intense luminescent colors (orange, yellow, and green) by adjusting the pH of the 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 in ORMOSIL sol systematically changes to orange, yellow, and green emissions, respectively. Interestingly, the structure of such surface-modified CDs can be well-preserved in the ORMOSIL film-matrix with substantial concentration to obtain the above tricolor luminescent films on glass. A systematic X-ray photoelectron spectroscopy 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 (−CONH– → −CO­(N<sup>–</sup>)–; −NH<sub>3</sub><sup>+</sup> → −NH<sub>2</sub>) 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 has been explored.