pH-driven chromophore amplification enables high-efficiency phosphorescent carbon dots

The solvothermal method is the most predominant synthetic approach for synthesizing carbon dots (CDs) phosphorescent materials. Understanding the influence of solvothermal reaction conditions on the phosphorescent properties of CDs is critical. Particularly, the regulation of pH environment plays a critical role in the solvothermal reaction process, because pH condition modulates the hydrolysis process of the precursor and the kinetics of the carbon core, or the structure of CD surfaces. However, the systematic impact of the specific pH modulation on the phosphorescent behavior of CDs has not been systematically investigated. In this paper, three CDs under distinct solvothermal pH conditions (pH 9.5, 11, and 12) were fabricated, and the relationship between synthesis pH value, the number of carbonyl groups on the surface of CDs and phosphorescent quantum yields (Φ_p) of CDs is revealed for the first time. By adjusting the pH, the Φ_p values of CDs increased progressively from 0.4 % (pH 9.5) to 0.58 % (pH 11) and 1.69 % (pH 12). Combined experimental and computational analyses, we propose that this enhancement arises primarily from increased density surface-bound carbonyl chromophores.