In a recent paper [Journal of Physical Chemistry C 122, 18751 (2018)], E. Díaz et al. have studied Förster resonant energy transfer (FRET) with upconverting nanoparticles (UCNPs) as donors and quantum dots (QDs). In this work, they use time-resolved luminescence spectroscopy to analyze the UCNP-to-QD FRET and focus on the most relevant parameter of the FRET phenomenon, UCNP−QD distance. This distance is controlled by a nanometric silica shell around the UCNP surface. They theoretically reproduce the experimental results applying FRET theory to the distribution of emitting erbium ions in the UCNP. This simple model allows them to estimate the contribution of every erbium ion to the final FRET response.

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