Stokes shift

Stokes shift is the distance between the peak absorption and peak emission wavelengths. It is the difference in wavelength between absorbed and emitted quanta, in wavelength shifters or scintillators. The emitted wavelength is always longer (if single photons are absorbed) or equal to the incident wavelength, due to energy conservation; the difference is absorbed as heat in the atomic lattice of the material.

It is named after Irish physicist George G. Stokes.