One-step preparation of nitrogen-doped and surface-passivated carbon quantum dots with high quantum yield and excellent optical properties

Abstract

Nitrogen-doped carbon quantum dots (N-CQDs) are prepared via one-step hydrothermal processing using citric acid and linear-structured polyethyleneimine (LPEI) polymer as raw materials. The LPEI serves not only as a nitrogen source for N-doping but also as a surface-passivation agent for surface modification. The as-obtained N-CQDs show a mean size of 1.67 nm and a high fluorescence quantum yield (QY) of 37.4%. In addition, with the remaining LPEI on the surface, the N-CQDs also show good water-solubility and reducibility for noble metal ions to construct CQDs-containing composites. After a set of careful examinations of the as-obtained N-CQDs, the so-called up-conversion photoluminescence (UCPL) of CQDs under an excitation of a xenon lamp, which are observed in previous reports, is found to be a false appearance caused by the second-order diffraction light from the monochromators of the spectrofluorimeter.