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Confinement-dependent exciton and biexciton dynamics in bright band-gap-emitting AgInS2 quantum dots

Julian G. Mann1, Johannes Kunze1, Nivedita Pan1, Ekaterina Kostyurina2, Markus Döblinger3, Bert Nickel2, Jochen Feldmann1,*, and Sushant Ghimire1,†

  • *Contact author: feldmann@lmu.de
  • †Contact author: sushant.ghimire@lmu.de
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Phys. Rev. B 114, 125420 – Published 26 August, 2026

DOI: https://doi.org/10.1103/9nj2-4hb1

Abstract

I-III-VI quantum dots are potential candidates for light-emitting and light-harvesting applications due to their heavy-metal–free composition and chemical tunability. Despite their potential, the investigation of intrinsic exciton and excitonic many-body dynamics has often been complicated because of their extensive defect energy landscape. Here, we investigate bright band-gap-emitting AgInS2 quantum dots of sizes ranging from ∼4 to 7 nm using femtosecond pump-probe spectroscopy to link quantum confinement to exciton formation and many-body interactions. The exciton formation time is governed by inter-valence-band hole relaxation. This increases by more than a factor of 4 with decreasing quantum dot size, reflecting size-dependent exciton-phonon scattering efficiency. By temporally correlating hole relaxation with induced absorption dynamics, we identify different exciton-to-biexciton transitions originating from different exciton states. Excitation-fluence-dependent measurements reveal a biexciton decay time that scales with the quantum dot volume. Smaller quantum dots show fast decay of <100 ps, primarily governed by exciton-exciton annihilation. In larger quantum dots, the biexciton lifetime exceeds 400 ps, indicating reduced annihilation efficiency. Complementary streak-camera photoluminescence experiments provide direct spectroscopic evidence that these long-lived biexcitons are partially emissive. Collectively, we report an in-depth ultrafast-optical study yielding fundamental insights into the complex landscape of exciton formation and biexciton physics, which advances the understanding of intrinsic optical processes in AgInS2 quantum dots among I-III-VI materials.

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Phys. Rev. B 114, 125420– Published 26 August, 2026
  • Received 16 June 2026
  • Revised 3 August 2026
  • Accepted 4 August 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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