Practice question

Quantum efficiency quantifies how effectively absorbed photons convert to fluorescence. Defined as ratio of photons emitted to photons absorbed, symbol Φ, ranging zero to one. It equals radiative rate divided by sum of radiative plus all non-radiative decay rates, including internal conversion, collisional quenching and intersystem crossing. Bright fluorophores exhibit high yield approaching unity, dim ones lose energy via heat. This parameter distinct from molar absorptivity or absorbance logarithm. Determination uses reference dyes of known yield, crucial for selecting probes for quantitative imaging.