Bright and tunable photoluminescence from the assembly of red g-C3N4 nanosheets

It is challenging to construct g-C3N4 (normally as a photocatalyst) with tunable and stable photoluminescence (PL) in solution or in powder form. In this paper, a molten-salt-assisted route has been developed to create red superior thin carbon nitride (g-C3N4) nanosheets with redshifted absorption spectrum and narrowed bandgap of 1.91 eV. Interestingly, these g-C3N4 nanosheets exhibit excellent water soluble nature. The colloidal solution of the nanosheets reveals bright, stable, and tunable PL from blue to yellow. The PL of samples depends on the concentration of g-C3N4 nanosheets. At lower concentration, a blue-emitting band is observed, while a green to yellow emitting band is recorded at higher concentration. Namely, the powder sample reveals a broad green to yellow emitting band. A reversible PL phenomenon is observed by precipitation of g-C3N4 colloidal solution. This phenomenon is ascribed to the assembly of these g-C3N4 nanosheets. The PL efficiency of red-coloured g-C3N4 nanosheets powder is 75%. Both powder and colloidal solution g-C3N4 samples reveal excellent PL stability. The PL intensity and efficiency of the powder samples remain almost unchanged after half year. These water-soluble red g-C3N4 nanosheets thus can be effectively utilized for light emitting diodes and bioimages.