Upconversion of photons

Patent Pending Photon upconversion (UC) is a process in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength. It is an anti-Stokes type emission. An example is the conversion of infrared light to visible light.[1][2][3] Materials by which upconversion can take place often contain ions of d-block and f-block elements. Examples of these ions are Ti2+, Ni2+, Mo3+, Re4+, and Os4+.