Nanostructure and optical property tuning between the graphitic-like CNx and fullerene-like β-C3N4 via Fe doping and substrate temperature

The Fe-doped CNx thin films were synthesized by the plasma enhanced chemical vapor deposition method. The structural and optical properties of the films with varying Fe concentration and substrate temperature were investigated. The studies can be divided into two parts: (Ι) with the increase of Fe concentration at room temperature, the sp3-hybridized C-N (fullerene-like) is decreasing opposite to the sp2 C-N (graphitic-like), inducing the tunable optical band gaps and red-shift photoluminescence (PL) emission peaks; (Ⅱ) increasing the substrate temperatures makes the nano-structural transformation from graphitic-like CNx to fullerene-like β-C3N4, decreased band gaps and blue-shift PL peaks. Based on these technologies, we obtained a self-standing film, consisting of the nano-crystallized β-C3N4 and amorphous carbon nitride. The optical absorptivity in the ultraviolet region of 200–400 nm can be reached up to >98% for all samples. The electron-hole recombination mechanism for the transition metal doped carbon nitride films was further elaborated.