Efficient Up-Conversion in CsPbBr3 Nanocrystals via Phonon-Driven Exciton-Polaron Formation

Abdullah S. Abbas; Beiye C. Li; Richard D. Schaller; Vitali B. Prakapenka; Stella Chariton; Gregory S. Engel; A. Paul Alivisatos

arXiv · 2312.07810

Efficient Up-Conversion in CsPbBr3 Nanocrystals via Phonon-Driven Exciton-Polaron Formation

Abdullah S. Abbas·Beiye C. Li·Richard D. Schaller·Vitali B. Prakapenka·Stella Chariton·Gregory S. Engel·A. Paul Alivisatos

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Abstract

Lead halide perovskite nanocrystals demonstrate efficient up-conversion, although the precise mechanism remains a subject of active research. This study utilizes steady-state and time-resolved spectroscopy methods to unravel the mechanism driving the up-conversion process in CsPbBr3 nanocrystals. Employing above- and below-gap photoluminescence measurements, we extract a distinct phonon mode with an energy of ~7 meV and identify the Pb-Br-Pb bending mode as the phonon involved in the up-conversion process. This result was corroborated by Raman spectroscopy. We confirm an up-conversion efficiency reaching up to 75%. Transient absorption measurements under conditions of sub-gap excitation also unexpectedly reveal coherent phonons for the subset of nanocrystals undergoing up-conversion. This coherence implies that the up-conversion and subsequent relaxation is accompanied by a synchronized and phased lattice motion. This study reveals that efficient up-conversion in CsPbBr3 nanocrystals is powered by a unique interplay between the soft lattice structure, phonons, and excited states dynamics.

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Abdullah S. Abbas, Beiye C. Li, Richard D. Schaller, Vitali B. Prakapenka, Stella Chariton, Gregory S. Engel, A. Paul Alivisatos. 2023-12-13. Efficient Up-Conversion in CsPbBr3 Nanocrystals via Phonon-Driven Exciton-Polaron Formation. https://arxiv.org/abs/2312.07810

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