Energy Transfer Upconversion
نویسنده
چکیده
The usual fluorescence behavior follows Stokes law, where exciting photons are of higher energy than emitted photons. Anti-Stokes processes usually concern emitted energies in excess of excited energies by only a few kT. These processes include anti-Stokes emission by the thermal bands or by the Raman effect. There are processes, however, in which emission photon energy exceeds excited photon energy by 10 100 kT. This includes energy transfer upconversion (APTE or ETU), multi-step excitations from excited state absorption (ESA), cooperative upconversion, and the photon avalanche effect. These upconversion processes are compared with the relative efficiencies for second harmonic generation (SHG) and 2-photon absorption (TPA) in Fig. 1.
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