Upconverting nanoparticles (UCNPs) have been of crucial significance in multiple applications involving photochemical, biomedical and optical ones. For the biomedical applications, one main problem that always stands as a challenge, hindering the upconversion scheme from being deployed inside human cells, is the challenging trade-offs among biomedical and field enhancement requirements imposed by the biomedical design constraints that deprive the UCNPs from field enhancement. Another challenge is imposed due to the constraint on the material choice that should achieve the required targeting, treatment/imaging, and electromagnetic design objective without any harm threatening the human body, which involves the dose limited by biodegradability and biocompatibility of the material. Although multiple field
enhancement and manipulation techniques have been applied to UCNPs, there has never been an exhaustive review on applicability of all possible field enhancement or tuning mechanisms in biomedical applications. In this work, an exhaustive review over all possible upconverting nanoparticles field enhancement and emission wavelength manipulation mechanisms is provided, organized, suggesting the potential of new techniques and discussing the applicability of each in biomedical applications.