Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2021 / Paper 2A / Section B / 22 / a / iv

For a fluorescence excitation spectrum, hold the emission detector at a fixed wavelength within the fluorescence band and scan the excitation wavelength. Correct for the incident photon flux and instrumental response at each excitation wavelength.

For one emitting molecular species with an approximately excitation-independent fluorescence yield, it should follow the absorption spectrum. In a dilute sample the detected emission is proportional to the photons absorbed, $I_{\mathrm{exc}}(1-10^{-A}){\varphi }_F\simeq I_{\mathrm{exc}}(\ln 10)A{\varphi }_F$. Without the dilute approximation it follows absorptance rather than absorbance exactly. Impurities, photochemistry or multiple emitting states could invalidate that correspondence.