Upconversion
Refers to the emission of light when certain characterstics are met with Phosphorous and Lanthanoid elements
A Sciencedirect.com webpage discusses the use of upconversion for the detection of 1.3μm luminescence.
"Conversion of IR radiation with λ=1.3 μm into the visible by use of nonlinear sum-frequency mixing in a LiIO3 crystal was studied experimentally. Advantages and disadvantages of the up-conversion method compared with other methods for NIR-light detection are discussed."
Lanthanoid elements when "upconverted" emit light.
One can also make upconversion more complicated as in this article from
University of California Santa Barbaranotice the time-resolving upconversion process.
This seems to be a great explanation of upconversion:
Upconversion involves the "mixing' of two wavelengths of light in a
nonlinear crystal to produce photons at an energy equal to the sum of
the two incident photon energies. This process only occurs when the
incident photons overlap in space, and more importantly, in
time.
Our 'crystal' are the elements in the Lanthanoid column. One can use many Lanthanoid elements to produce different upconversion responses on a light response emission.
Upconversion fluorescence imaging technique with excitation in the near-infrared (NIR) region has been used for imaging of biological cells and tissues. This has several advantages, including absence of photo-damage to living organisms, very low auto-fluorescence, high detection sensitivity, and high light penetration depth in biological tissues.
The near-infrared region is also called Infra Red-A
Also there is an "Energy Upconversion" Discussed in the following
PNOS.org webpage excerpt:
The photophysical events preceding electron transfer in green plant and bacterial photosynthesis have been the subject of much speculation and experiment (1-8).