Efficient up-conversion in CsPbBr3 nanocrystals via phonon-driven exciton-polaron formation

• Published in: Nature communications Vol. 16; no. 1; pp. 5803 - 8
• Main Authors: Abbas, Abdullah S., Li, Beiye C., Schaller, Richard D., Prakapenka, Vitali B., Chariton, Stella, Bian, Daqian, Engel, Gregory S., Alivisatos, A. Paul
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 140/133; 147/143; 639/301/357/1017; 639/638/440/527/1821; 639/638/440/949; 639/766/400/584; Coherence; Cooling; Crystals; Efficiency; Energy; Excitation; Excitons; Fourier transforms; Humanities and Social Sciences; Lasers; Lattice vibration; Lead compounds; Metal halides; multidisciplinary; Nanocrystals; Nanomaterials; Perovskites; Phonons; Photoluminescence; Photons; Raman spectroscopy; Science; Science (multidisciplinary); Semiconductors; Spectroscopy; Spectrum allocation; Spectrum analysis; Thin films; Upconversion; Vibrations
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-025-60992-y

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 CsPbBr 3 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 CsPbBr 3 nanocrystals is powered by a unique interplay between the soft lattice structure, phonons, and excited states dynamics. Here, the Authors show that up-conversion in CsPbBr3 nanocrystals arises from an interaction between soft lattice vibrations and excited states, with a specific phonon mode enabling coherent and highly efficient up conversion process.