Light-energy upconversion

As a final example of manipulating the optical properties a material to produce a desired effect, upconversion is considered (Risk et ak, 2003). In one sense this is similar to nonlinear optical processes since the net result is the production of high-energy light from low-energy light. However, the details are different. One immediate advantage... 

Upconversion materials, which emit high-energy photons under excitation by the NIR light (anti-Stokes shift) were first discovered in the 1960s, but have primarily been exploited for the development of some remarkably effective optical devices such as infrared quantum counter detectors, ... 

Upconversion is a process where low-energy light, usually near-infrared (NIR), is converted to higher-energy (visible) light via multiple absorptions or energy transfer processes. 

Activator In energy transfer upconversion (ETU) process, an activator receives energy from the nearby excited ions and releases an emission light with a specific wavelength. 

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