Excitonic optical properties in monolayer SnP₂S₆

Quantum confinement effect and reduced dielectric screening in two-dimensional (2D) dramatically enhance the electron–hole interactions. In this work, we use many-body perturbation theory and Bethe–Salpeter equation (BSE) to investigate the electronic and excitonic optical properties of monolayer SnP₂S₆. Our findings reveal that the excitonic effect dominates the optical absorption spectra in the visible light range, and the lowest-energy exciton X₀ in monolayer SnP₂S₆ is optically bright with the binding energy of 0.87 eV and the radiative lifetime of ∼ 10⁻¹¹ s, which is highly advantageous to the photo-luminescence. Most importantly, the absence of optically forbidden states below the bright states X₀ would give rise to a high quantum efficiency of 2D SnP₂S₆. We also find that applied biaxial strain can further shorten the radiative lifetime of the bright states. These results imply that 2D SnP₂S₆ is a promising candidate for the optoelectronic devices.