This Brief presents a historical overview of the Foerster-type nonradiative energy transfer and a compilation of important progress in FRET research, starting from Foerster until today, along with a summary of the current state-of-the-art. Here the objective is to provide the reader with a complete account of important milestones in FRET studies and FRET applications as well as a picture of the current status.

This Brief presents a complete study of the generalized theory of Foerster-type energy transfer in nanostructures with mixed dimensionality. Here the aim is to obtain a generalized theory of FRET including a comprehensive set of analytical equations for all combinations and configurations of nanostructures and deriving generic expressions for the dimensionality involved. In this brief, the modification of FRET mechanism with respect to the nanostructure serving as the donor vs. the acceptor will be included, focusing on the rate's distance dependency and the role of the effective dielectric function in FRET, which will be a unique, useful source for those who study and model FRET.

This Brief will focus on the functional uses and applications of FRET, starting with the derivation of FRET in the assemblies of nanostructures and subsequently giving application cases for biologists, physicists, chemists, material scientists, engineers, and those in many other fields whoever would like to FRET as a tool. The goal of this part is therefore to show both specialist and non-specialist how to use and analyze FRET in a wide range of applications.