biostudies-literatureKluherz KTBasic Energy SciencesNational Renewable Energy LaboratoryBrookhaven National Laboratory30436-30446https://www.ebi.ac.uk/biostudies/studies/S-EPMC12371897biostudies-literatureUnknown147(33)The expression of metal lone-pair electrons is hypothesized to underpin many of the interesting properties of inorganic halide perovskite semiconductors. Recently, a stable low-temperature monoclinic polar phase was predicted for CsSnBr₃ and CsSnI₃, opening the possibility of direct investigation of a ferroelectric distorted structure compared to the undistorted structure. To date, there have been no experimental reports of such a structure in CsSnI₃, and the low-temperature optical properties of CsSnI₃ nanocrystals have remained unexplored. Here we report optical and structural evidence of a phase transition around 240 K in 8.9 nm CsSnI₃ nanocrystals. Several changes in optical behavior occur below this transition point, including high-energy photoluminescence (PL) that emits concurrently with the exciton PL. The emergence of this high-energy PL is correlated with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) supporting a phase transition from the orthorhombic structure between 240-200 K. Transient absorption measurements show an increase in the excited state lifetimes, i.e., slowed carrier cooling, at 200 K when photoexciting with photon energies above the high-energy state, consistent with slowed carrier cooling and emergence of high-energy PL. We hypothesize that the slowed carrier cooling is distinctive to this phase transition that modifies both the electronic and phonon structures that dictate excited-state carrier dynamics, and we discuss these changes.Journal of the American Chemical SocietyDual Photoluminescence in Low-Temperature Phase of CsSnI<sub>3</sub> Nanocrystals.PMC12371897DE-SC0012704DE-AC36-08GO28308Weadock NJSercel PCBeard MCKluherz KTShelton JLLeick NfalseDual Photoluminescence in Low-Temperature Phase of CsSnI<sub>3</sub> Nanocrystals.The expression of metal lone-pair electrons is hypothesized to underpin many of the interesting properties of inorganic halide perovskite semiconductors. Recently, a stable low-temperature monoclinic polar phase was predicted for CsSnBr₃ and CsSnI₃, opening the possibility of direct investigation of a ferroelectric distorted structure compared to the undistorted structure. To date, there have been no experimental reports of such a structure in CsSnI₃, and the low-temperature optical properties of CsSnI₃ nanocrystals have remained unexplored. Here we report optical and structural evidence of a phase transition around 240 K in 8.9 nm CsSnI₃ nanocrystals. Several changes in optical behavior occur below this transition point, including high-energy photoluminescence (PL) that emits concurrently with the exciton PL. The emergence of this high-energy PL is correlated with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) supporting a phase transition from the orthorhombic structure between 240-200 K. Transient absorption measurements show an increase in the excited state lifetimes, i.e., slowed carrier cooling, at 200 K when photoexciting with photon energies above the high-energy state, consistent with slowed carrier cooling and emergence of high-energy PL. We hypothesize that the slowed carrier cooling is distinctive to this phase transition that modifies both the electronic and phonon structures that dictate excited-state carrier dynamics, and we discuss these changes.2025-01-01T00:00:00Z2025 Aug2026-05-09T10:41:06.765Z2026-04-08T00:48:33.954ZS-EPMC123718974076796110.1021/jacs.5c10595