Birch, et al., have shown that fluorescence anisotropy-decay in sols with two rotational correlation times can be explained by the existence of silica particles. This interpretation allows monitoring sol-gels in situ with sub-nanometer resolution. Because a fluorophore immobilized in a gel does not de- polarize fluorescence, one can study particle size well after the sol-to-gel transition time, a major advantage over scattering techniques (e.g., with neutrons or X-rays) where gel-scattering distorts the scattering function.

Moreover, the rapid data-acquisition needed to acquire anisotropy-decay data within time-spans as short as a few minutes is aided greatly by the high-repetition rate of the NanoLED excitation sources from HORIBA Jobin Yvon.