Morphology-Dependent One- and Two-Photon Absorption Properties in Blue Emitting CsPbBr3 Nanocrystals

Origin of the low-energy tail in the photoluminescence spectrum of CsPbBr3 nanoplatelets: a femtosecond transient absorption spectroscopic study

CsPbBr3 nanoplatelets (NPLs), as some of the two-dimensional lead halide perovskites, have been intensively investigated due to their outstanding photophysical and photoelectric properties. However, there remain unclear fundamental issues on their carrier kinetics and the low-energy tail in their photoluminescence (PL) spectrum. In this paper, we synthesized CsPbBr3 NPLs with five [PbBr6]4- monolayers and performed comprehensive studies by using steady-state absorption, PL, and femtosecond transient absorption (fs-TA) spectroscopic measurements. We determined both the biexciton Auger recombination time (7 ± 2 ps) and trapped exciton lifetime (110 ± 15 ps) of the five monolayer CsPbBr3 NPLs. We also investigated the origin of the low-energy tail emission in their PL spectrum. More importantly, we found that a negative ΔA feature in the energy range of 2.45-2.55 eV appears in their fs-TA spectrum at 2, 4 and 10 ps delay times, which could help them act as a laser gain medium. The low-energy tail emission in their PL spectrum overlaps well with the negative ΔA feature in the energy range of 2.45-2.55 eV in their fs-TA spectrum at 2, 4 and 10 ps delay times.

Aspect Ratio and Quantum Confinement Tunable Giant Two-Photon Absorption from 1D CsPbI3 Perovskite Nanorods

Herein, we investigate the influence of aspect ratio and quantum confinement on the single-photon (σ1) and two-photon absorption cross-section (σ2) for perovskite CsPbI3 nanorod (NR). Notably, experimentally measured data show extremely high σ2 for CsPbI3 NR (10.8 × 107 GM) which is five orders of magnitude higher than organic chromophores, and two order of magnitude higher than CsPbBr3 nanocrystals. Moreover, σ2 for NRs can be enhanced by two-orders of magnitude by varying the aspect ratio and σ1 enhances linearly with aspect ratios. Furthermore, experimental data show moderate quantum confinement effect on the volume-normalized σ1 and σ2 for nanorods.

Temperature-Dependent Intensity Modulated Two-Photon Excited Fluorescence Microscopy for High Resolution Mapping of Charge Carrier Dynamics

We present a temperature-dependent intensity modulated two-photon excited fluorescence microscopy technique that enables high-resolution quantitative mapping of charge carrier dynamics in perovskite microcrystal film. By disentangling the emission into harmonics of the excitation modulation frequency, we analyze the first and second order charge carrier recombination processes, including potential accumulation effects. Our approach allows for a quantitative comparison of different emission channels at a micrometer resolution. To demonstrate the effectiveness of the method, we applied it to a methylammonium lead bromide perovskite microcrystal film. We investigated the temperature-dependent modulated imaging, encompassing the exciton dissociation-association and charge carrier trapping-detrapping equilibrium. Additionally, we explored the potential freezing out of traps and the phase transition occurring at low temperatures.