Precise fluorescence measurement for determination of photophysical properties of dyes

Abstract

The authors present a double frequency modulation technique to determine the fluorescence power with an accuracy of at least 10 −5. Quantitative analysis of the modulation transfer from the excitation to the fluorescence power is used to derive the triplet state lifetime τ DS and the rate constant for intersystem crossing k ED of fluorescent dyes. For that purpose the correlation between the population of transient states and the decrease of fluorescence power is measured. The experimental results of rhodamine 6G are presented. The influence of molecular oxygen is also examined. The photophysical parameters can be determined with high accuracy even if absorption of excited states, photoproducts or other molecules is present. This sensitivity is sufficient to determine the presence of a few hundred molecules in excited states.