Termination-Dependent Synchronous Tuning of Bright- and Dark-Exciton Radiative Lifetimes in Fullerene-Based C36-2D Heterostructures.

Excitons play a central role in optoelectronic, quantum-information, and energy conversion processes, and understanding their radiative recombination behavior is essential for exciton regulation in low-dimensional materials. Here, we employed density functional theory and many-body perturbation theory within the GW-Bethe-Salpeter equation (GW-BSE) framework to systematically investigate the quasiparticle and excitonic properties of a-C36-2D monolayers and SnXY/a-C36-2D heterostructures. The a-C36-2D monolayer exhibits pronounced excitonic effects, with an exciton binding energy of 1.01 eV and bright- and dark-exciton radiative lifetimes on the order of 10-14 and 10-7 s, respectively. Upon heterostructure construction, the exciton binding energies are reduced due to type-II band alignment-induced electron-hole separation and the additional dielectric screening introduced by the SnXY layers. Meanwhile, different SnXY terminal configurations provide an effective approach for tuning bright-exciton radiative lifetimes by regulating transition dipole strengths, enabling lifetime modulation from the 10-12 to 10-11 s range. Furthermore, the reduced interfacial symmetry relaxes parity-related dipole selection rules, leading to finite oscillator strengths of originally dark excitons and shortening their radiative lifetimes from the 10-7 s level to the 10-9 s level. These radiative lifetimes are evaluated from oscillator strengths and transition dipole moments obtained from GW-BSE calculations and therefore characterize the intrinsic radiative recombination of the excitons rather than their total population decay. The combination of large exciton binding energies and broadly tunable radiative lifetimes provides microscopic insight into exciton regulation in fullerene-based two-dimensional heterostructures.