Relaxation of Excited Electrons on Carbon Nitrides Investigated by Electrochemiluminescence and Photoluminescence Spectra

Deep insights into the photoexcitation and relaxation of carbon nitrides are vital to developing highly efficient photocatalysts and luminescence-based applications. In this work, carbon nitride nanosheets are prepared by thermal-induced self-condensation of melamine under atmospheric conditions followed by liquid exfoliation in water. The photolumninescence (PL) quantum yield decreases, but the electrochemiluminescence (ECL) intensity enhances with the increase in pyrolytic temperature. Besides, the PL peak broadens and concomitantly red shifts with the increasing temperature, whereas the ECL spectra keep nearly the same lineshapes. The different features of ECL and PL indicate different pathways of excited state transitions, which allows for a thorough understanding on the electronic structures. The excited energy level emitting at 450 nm, at which the excited electrons at this level show longer lifetime and can be effectively excited via electric injection, is found to be a highly active transportation channel. In view that carbon nitrides are a class of layered materials, it is foreseen that the combination of the PL and the ECL techniques could provide useful information on the excited state transition process in other layered nanomaterials.