DOI: https://doi.org/10.29363/nanoge.emlem.2023.037
Publication date: 18th August 2023
Lanthanide-doped nanocrystals are promising for light sources in the ultraviolet, visible, and infrared regime because of their rich energy-level structure.[1, 2] However, the low absorption cross-section of these luminescent ions limits the brightness of lanthanide-based devices. A common strategy to boost the brightness is to increase the density of lanthanide ions. At higher lanthanide-ion densities, energy transfer from ion to ion causes diffusion of energy through the nanocrystal. This can lead to quenching on defects or chemical moieties on the nanocrystal surface.
In this work, we synthesized LiYF4 nanocrystals containing either erbium or ytterbium ions[3] of varying doping concentrations. We find that the photoluminescence quantum yield of both types of nanocrystals decrease with increasing doping concentrations. Ytterbium and erbium have various emitting levels in the near-infrared and visible spectrum range. These levels exhibit qualitatively different changes in excited-state dynamics at increasing doping concentrations, indicating different quenching pathways at play. We can understand the results in terms of energy diffusion, quenching sites at the surface, and/or cross-relaxation. By combining the concentration-dependent quantum yield and excited-state dynamics, we learn more about the microscopic nature of the quenching sites on the surface. This showcases the importance of spectroscopic measurements to characterize defects in nanomaterials.
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