Number of defined events occurring per photonabsorbed by the system.
The integral quantum yield is
For a photochemical reaction
The differential quantum yield is
is the rate of change of a measurable quantity
(spectral or any other property), and
the amount of photons
or its equivalent
(prior to absorption) per time interval (photon flux, amount basis).
is the absorbance
at the excitation wavelength
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 406