Speaker
Description
Ag₂S-based nanocrystals (NCs) emerged in the recent years as highly promising emitters for deep-tissue imaging and luminescence nanothermometry. Their assets combine efficient NIR luminescence in the second biological window (1000 – 1350 nm), low cytotoxicity and large absorption cross-section. In this contribution we will focus on the light emission and photophysics properties of Ag2S NCs with different surface passivation. We will show how the nature of surface passivation plays an important role on their temperature-dependent photoluminescence properties and ultrafast excited-state dynamics.[1,2] By comparing plain Ag₂S NCs, Ag/Ag₂S NCs, and highly emissive surface-passivated Ag₂S NCs with graded Se/Zn shells, we show that surface chemistry critically determines their optical performance. Temperature-dependent measurements reveal strong thermal quenching of the infrared emission, enabling thermal sensing with high sensitivity, while also showing that the thermal stability of the photoluminescence quantum yield is crucial for practical imaging performance under physiological conditions. In particular, surface-passivated nanocrystals exhibit improved robustness against temperature-induced emission losses in aqueous media. Femtosecond transient absorption spectroscopy further shows that passivation sharpens excitonic resonances and suppresses defect-assisted recombination.[3] At low excitation densities, the dynamics are governed by trapping and exciton recombination, whereas at higher fluences biexciton and Auger recombination become significant. Faster multi-exciton recombination in passivated samples highlights the strong impact of surface engineering on many-body interactions.
Keywords: nanocrystals, luminescence, imaging, photophysics
[1] D. Ruiz et al., Adv. Funct. Mater. 2017, 1604629.
[2] P. Wang et al., Mater. Horiz. 2024,11, 6158-6168.
[3] V. Vega-Mayoral et al., Nanoscale, 2025, 17, 15697