The work described herein explores the field of metal–organic frameworks (MOFs) with a particular emphasis on rare-earth (RE) cluster-based MOFs. MOFs are materials that are of interest due to their permanent porosity, high surface areas, and tunable structures. This thesis focuses on three different MOFs: RE-UiO-66 (UiO = University of Oslo), RE-CU-10 and RE-CU-27 (CU = Concordia University). The synthesis, characterization, and photophysical properties of these MOFs are presented. Chapter 2 explores tuning of the RE-UiO-66 platform by synthesizing and characterizing mono-, bi- and tri-metal RE-UiO-66 analogues where RE = Tb(III), Gd(III), and Eu(III), ultimately leading to the formation of a white light emitting MOF. Furthermore, a study of the photophysical properties of this series of MOFs is conducted and as a proof of concept, Tb:Gd:Eu-UiO-66 is deposited on a UV light emitting diode (LED), leading to a white light emitting diode (WLED). Chapter 3 describes a facile route for modulating the photoluminescent and radioluminescent properties of Tb(III) cluster-based MOFs. By using Tb(III)-cluster nodes as Xray attenuators, and organic linkers with varying excited state energies as sensitizers, MOFs with metal-based, linker-based, and metal+linker-based photo- and radioluminescence are reported.