Coherent exciton-lattice dynamics in a 2D metal organochalcogenolate semiconductor

We reveal coherent exciton-phonon interactions in the two-dimensional (2D) layered hybrid organic-inorganic semiconductor silver phenylselenolate (AgSePh). Using femtosecond resonant impulsive vibrational spectroscopy and non-resonant Raman scattering, we identify multiple hybrid organic-inorganic vibrational modes that strongly couple to the excitonic transitions and characterize their behavior. Calculations by density functional perturbation theory show that these strongly coupled modes exhibit large out-of-plane silver atomic motions and silver-selenium spacing displacements. Moreover, analysis of photoluminescence spectral splitting and temperature-dependent peak shifting/linewidth broadening reveals that light emission in AgSePh is most strongly affected by a compound 100 cm−1 mode involving the wagging motion of phenylselenolate ligands and accompanying metal-chalcogen stretching. Finally, red shifting of vibrational modes with increasing temperature reveals a high degree of anharmonicity arising from non-covalent interactions between phenyl rings. These findings reveal the unique effects of hybrid vibrational modes in organic-inorganic semiconductors and motivate future work aimed at specifically engineering such interactions through chemical and structural modification.