This article focuses on lanthanide-based upconversion phosphors that have drawn significant interest in the field of material science and biomedicine for targeted drug delivery. The unique optical and chemical properties of lanthanide ions for having at least one electron in the 4f orbital make it suitable for upconversion. Upconversion nanoparticles (UCNPs) possess distinctive attributes, including autofluorescence, a high signal-to-noise ratio, minimal photodamage to living organisms, and deep penetration in biological samples, which render them highly suitable for drug delivery applications. UCNPs appear to be a suitable drug-making technique that can be used to treat cancer with nearly minimal side effects, among other applications. Upconversion materials play a critical part in sensing applications. Utilizing these nanoparticles allows for the conversion of longer wavelength photons into shorter wavelength fluorescence, enabling the detection of temperature, pH, ions, and trace biomolecules. Delivering the drug to the tumor site stands out as a primary issue, as the traditional approach of drug distribution in the biological context leads to various side effects in individuals. Researchers from many fields are interested in photodynamic treatment because of its capacity to activate the manufactured medicine during the upconversion process using light. Hence, there is a growing prominence of Ln3+-based upconversion materials, indicating their potential as groundbreaking options for new biomedical applications. This article review specifically examines the chemical makeup and development of upconversion nanoparticles, as well as the methods for creating targeted drug delivery systems. Additionally, the article delves into the application of these particles in different cancer treatment approaches, including therapies such as photodynamic therapy (PDT).