First-principles investigation of phonon-assisted photoluminescence in bilayer MoS₂

Phonon-assisted processes govern photoluminescence (PL) process in indirect band gap materials. Using a first-principles many-body framework, we investigate phonon-assisted PL in bilayer MoS₂ and its dependence on temperature and tensile strain. We capture phonon effects using a supercell approach, in which we identify the relevant phonon momenta for PL and construct commensurate supercells, followed by analysis of how atomic displacements along each phonon mode modify the optical absorption. The PL intensity is obtained from the absorption spectra via the van Roosbroeck–Shockley relation, allowing separate analysis of phonon-emission and phonon-absorption processes. In unstrained bilayer MoS₂, optical phonons involving out-of-plane S vibrations and in-plane Mo vibrations dominate the indirect PL. Finally, we also show that increasing tensile strain activates new phonon-assisted pathways in the PL spectra through electronic structure modulation.