Tailoring the unique delayed and long-lasting luminescence of persistent phosphors is crucial for their application in anticounterfeiting, data storage, imaging displays, and AC-driven lighting. We introduce a novel strategy to achieve this by modifying the refractive index of persistent phosphor transparent coatings. Specifically, we developed ZnGa2O4:Cr3+/SiO2 nanocomposite films with tunable refractive indices from 1.45 to 1.7. This tunability allowed us to precisely control the Cr3+ radiative decay rate, resulting in a substantial 1.7-fold increase in both luminescence and afterglow brightness. Furthermore, our approach uniquely influences the intrinsic charging rate of the phosphor, a mechanism attributed to the strain induced on the ZnGa2O4:Cr3+ nanocrystals by the presence of SiO2. This work demonstrates an unprecedent ability to manipulate the afterglow kinetics without altering the material composition, opening new avenues for designing and optimizing persistent luminescence materials.