THE STRUCTURE OF THE PHOTOLUMINESCENCE SPECTRA OF OXYGEN DOPED GRAPHITIC CARBON NITRIDE

Abstract

Evolution of photoluminescence spectra of graphitic-like carbon nitride synthesized by pyrolysis of melamine in closed oxygen containing air environment was studied in the temperature range of 10-300 K. It was shown that the oxygen concentration in the resulting material is 4-5 at. % and increases with the temperature and decreases with increasing of the synthesis process duration. Measurements at low temperatures up to 10 K made it possible to resolve several bands on the photoluminescence spectra of graphite-like carbon nitride associated with radiative recombination processes. It was found that an increase in the synthesis temperature from 500 to 600 °С as well as an increase in its duration from 30 to 240 min at a given temperature lead to a shift of photoluminescence spectrum maximum from 2.74 eV to the lower energy region of 2.71-2.67 eV. That shift is associated with the increasing role in light emission of the molecular system formed by π-bonds of carbon and nitrogen atoms with sp²-hybridization characterized by a smaller band gap. Transitions associated with recombination through oxygen-induced levels in the band gap of the semiconductor contribute to the appearance of a “tail” on the photoluminescence spectra in the low-energy region (2.4-2.33 eV). An increase in the temperature of carbon nitride synthesis to 600 °C leads to a change in the structure of energy zones and an increase in the energy of radiative transitions due to an increase in the oxygen doping level and thermal stratification.