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Following intense research on two-dimensional (2D) materials, there has been a resurgence of interest in 2D layered hybrid organic-inorganic perovskites. These 2D perovskites have direct band gaps regardless of their thickness. Excitons are confined to monolayers because of the materials' selforganized quantum-well electronic structure. Gaining insight into the exciton dynamics is central to understanding the light-matter interactions in 2D organic-inorganic perovskites. Herein, we investigate the free-exciton dynamics in 2D layered CH 3 (CH 2 ) 3 NH 3 PbI 4 perovskite, demonstrating an anomalous temperature variation of the photoluminescence (PL) energy, which deviates from the conventional Varshni formula and is consistent with the behaviour of Bose-Einstein oscillators. The acoustic phonons induced by the coherent lattice motion of the atoms result in a positive temperature variation. Two-pulse emission modulation measurements reveal the excitation mechanism of the strong two-photon PL in CH 3 (CH 2 ) 3 NH 3 PbI 4 perovskite, in which two photons are simultaneously absorbed through a virtual state.

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