Ultraviolet C(UVC) upconversion phosphors excited by visible light sources, particularly those with low excitation densities, such as semiconductor LED, fluorescent lamps, and sunlight, have great potential in nonsensitive labeling, anticounterfeiting, photocatalysis, and biological and urban environmental antimicrobial fields. To achieve visible light excitation, UVC upconversion phosphors require a long energy level lifetime in the first excited state, the ability to effectively absorb visible light photons, and a host material that can effectively transmit visible light and UVC. Rare-earth ions are shielded by their outer electrons and have abundant energy levels with a long lifetime; inorganic materials with high band gaps can effectively penetrate UVC. Therefore, inorganic luminescent materials doped with rare-earth ions are ideal choices for UVC upconversion phosphors owing to visible light excitation. However, their low UVC upconversion emission power limits their application. Thus, the greatest problem currently faced is improving the UVC upconversion power under low excitation densities. This work focuses on the development of UVC upconversion phosphors for visible light excitation, the current research status, and research solutions and methods in the field of low excitation densities.