Observation of biexciton emission in graphitic-C3N4 nanotubes

Highlights: • The g-C₃N₄ nanotubes are fabricated by a combination of probe-sonication and bath-sonication. • Biexciton emission is demonstrated in graphitic-C₃N₄ nanotubes. • Strong Coulomb attraction (47.1 meV) within the biexciton is observed. Multiexciton emission induced by strong carrier-carrier interaction is an important photophysical effect that may be utilized to generate entangled photons. In this work, the biexciton emission is demonstrated in graphitic-C₃N₄ nanotubes. The absorption cross section of the g-C₃N₄ nanotubes is about $1.14\times {10}^{-15}$ cm². Accordingly, the threshold of excitation fluence for biexciton is estimated to be 430 μJ/cm². As the excitation density increases from 237 to 750 μJ/cm², the dynamics of excited carriers exhibit a clear trend toward biexciton emission governed by the fast Auger recombination. And strong Coulomb attraction (47.1 meV) within the biexciton is observed. The biexciton recombination is then further verified by the faster PL decay at increasing carrier density.