Coherent Multi-Dimensional Spectroscopy Reveals Homogeneous Lineshape Dynamics in CsPbBr₃ Quantum Dots

Lead halide perovskite (LHP) quantum dots (QD) are an attractive material for light emissive applications due to their lattice, which is both dynamically disordered and defect tolerant. The development of LHP QD for quantum emitters critically depends on the characterization of their homogeneous lineshapes. Homogeneous lineshapes are measured by single dot photoluminescence spectroscopy only at cryogenic temperatures for which their lattice dynamics are frozen out. There are presently no experiments which reveal the lineshapes at 300 K, let alone their dynamics due to lattice fluctuations. Here, we perform coherent multi-dimensional spectroscopy (CMDS) on a broad size range of CsPbBr₃ QD at 300 K to observe homogeneous lineshapes and their dynamics on the femtosecond time scale of lattice motions. In contrast to linear spectroscopies, these nonlinear CMDS experiments unambiguously reveal that the room temperature homogeneous line widths are both narrow and size independent at 300 K. The ensuing femtosecond line shape dynamics is governed by size-dependent exciton-lattice interactions. These results demonstrate the potential of LHP QD for high-temperature quantum light sources.