Förster resonance energy transfer (ET) between luminescent species is applied in bioimaging, 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 LaPO 4 nanocrystals co-doped with Ce 3 þ donors and Tb 3 þ acceptors. Although the radiative emission rate of the Ce 3 þ excited state increases with the refractive index of the solvent in which the nanocrystals are dispersed, the Ce 3 þ -to-Tb 3 þ ET rate does not. We demonstrate that, as a result, lower refractive index solvents enable higher ET efficiencies leading to higher Tb 3 þ 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.

If organic molecules are to be used as the active component in devices, self-assembly represents the most attractive route to control the geometric structure and therefore part of the device performance. High-resolution scanning tunneling microscopy measurement combined with density functional theory and Monte Carlo calculations are used to study the stability of self-assemblies of molecules with bonding motifs spanning (nearly) the entire range of intermolecular interaction strengths. Our atomistic model reproduces the experimentally observed crystal structures with sub-Ångstrom precision in all cases. In addition, it is able to identify metastable structures through thermodynamic analysis.