Upconversion is a research area in the field of photonics and nanotechnology that focuses on the process of converting lower-energy photons into higher-energy photons. This process is typically achieved through the use of upconversion materials or nanoparticles that absorb multiple low-energy photons and emit a single higher-energy photon. Upconversion has many potential applications in fields such as solar energy conversion, bioimaging, and telecommunications. Researchers are actively studying different materials and techniques to improve the efficiency and versatility of upconversion processes.