This review presents an overview of various synthesis and characterization techniques used for rare earth activated phosphors intended for bioimaging applications. Here, various researchers developed the rare earth activated phosphors using a variety of synthesis techniques, including solid state, sol–gel, hydrothermal, combustion, etc. As reported in their studies, the resulting phosphors have been compared by using various characterization techniques for its structural analysis, morphological analysis, optical analysis, to assess their potential in bioimaging applications. Previously some authors have highlighted the importance of bioimaging phosphor to improve the quality of medical optical imaging and its low-cost effect. We can stimulate the biological window for tissue imaging experiments using rare earth activated phosphors. Herein, some important wavelength ranges relevant for tissue imaging fall within the biological optical window of 650–950 nm, where reduced absorption and scattering enable deeper light penetration into biological tissues. Current phosphors have a significant drawback that they are only ideal for one time use because their persistent brightness fades after a few hours. To address this problem, persistent phosphors with photo-stimulated properties are used. In this article, an in-depth assessment has been provided that surely will be a good resource for researchers in exploring various fields related to biomedical imaging.