Photonic effects on the Förster resonance energy transfer efficiency.

Förster resonance energy transfer (ET) between luminescent species is applied in bio-imaging, lighting and photovoltaics, and has an important role in photosynthesis. However, the fundamental question of whether ET rates and efficiencies can be tuned by the photonic environment remains under debate. Here we show that ET rates are independent of the photonic environment, using the model system of LaPO4 nanocrystals co-doped with Ce(3+) donors and Tb(3+) acceptors. Although the radiative emission rate of the Ce(3+) excited state increases with the refractive index of the solvent in which the nanocrystals are dispersed, the Ce(3+)-to-Tb(3+) ET rate does not. We demonstrate that, as a result, lower refractive index solvents enable higher ET efficiencies leading to higher Tb(3+) emission intensities. Furthermore, an analytical model for ET in (nano)crystalline host materials is presented, able to predict the dependence of ET efficiencies on the photonic environment and the concentration of acceptor ions.