Due to their well-suited optoelectronic properties, metal halide perovskites are emerging semiconductor materials with potential applications in solar cells, detectors, and light-emitting diodes. Beyond the traditional 3D perovskites, low-dimensional counterparts have more attractive effects such as excitonic emissions and quantum confinements that are enhanced by the reduced dimensionality, which involve the electron-phonon coupling (EPC). Such phenomenon, which comprehends the interaction between charge carriers and lattice vibrations, usually strongly impacts the photoluminescence (PL) response in low-dimensional frameworks. In this paper, we investigated the intrinsic EPC onto low-temperature PL of the zero-dimensional (0D) ${\mathrm{Rb}}_2{\mathrm{SnBr}}_6$ perovskite. Temperature-dependent PL measurements, complemented by various characterization techniques and theoretical calculations, revealed broadband emission with a significant Stokes shift attributed to self-trapped excitons (STEs). The Fröhlich mechanism, mediated by interactions between excitonic charge carriers and longitudinal optical (LO) phonons, primarily accounts for the emission broadening through phonon-assisted radiative recombination. The EPC strength was evaluated through the Huang-Rhys factor $S=34$, confirming strong correlations between electronic and vibrational properties and supporting the STE emission assumption. The possible mechanism of STE formation was evaluated by the Fröhlich parameter $\alpha$ of 2.78 for electrons and 4.41 for holes, which points out a major contribution of the hole-polaron quasiparticle on exciton trapping. Our findings give insights regarding the influence of EPC in 0D perovskites and STE formation, which leads to the assessment of ${\mathrm{Rb}}_2{\mathrm{SnBr}}_6$ for light-harvesting applications.

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• Electron-phonon coupling
• Hybrid perovskites
• Infrared spectroscopy
• Luminescence
• Raman spectroscopy