How to measure quantum yields in scattering media: Application to the quantum yield measurement of fluorescein molecules encapsulated in sub-100 nm silica particles

Dye quantum yield is generally measured using the method of Williams, which consists in comparing the absorbance and the emission of the dye to test with those of a reference. Unfortunately, this method is no more applicable when the sample presents some significant scattering which is, for instance, the case when the dyes are encapsulated in silica particles with a size below 100 nm. Indeed the photons scattered by the particles are further absorbed by the dyes and generate an additional light emission leading to an overestimation of the quantum yield. Nevertheless, the paper shows that the Williams’s method can be still applied if the sample is compared with a reference that has exactly the same scattering properties than those of the sample. In the case of a test sample consisting of dyes encapsulated within particles, such a reference can be easily realized by incorporating in a solution of reference dyes, an adequate proportion of particles with the same size than those of the test sample. We prove theoretically and experimentally that relevant values of quantum yield are then obtained.