  Two-dimensional metal-halide perovskites are highly versatile for
light-driven applications due to their exceptional variety in material
composition, which can be exploited for tunability of mechanical and
optoelectronic properties. The band edge emission is defined by structure and
composition of both organic and inorganic layers, and electron-phonon coupling
plays a crucial role in the recombination dynamics. However, the nature of the
electron-phonon coupling and which kind of phonons are involved is still under
debate. Here we investigate the emission, reflectance and phonon response from
single two-dimensional lead-iodide microcrystals with angle-resolved polarized
spectroscopy. We find an intricate dependence of the emission polarization with
the vibrational directionality in the materials, which reveals that several
bands of the low-frequency phonons with non-orthogonal directionality
contribute to the band edge emission. Such complex electron-phonon coupling
requires adequate models to predict the thermal broadening of the emission and
provides opportunities to design its polarization properties.
