Our group has previously determined kTTA for compounds based on 9,10diphenylanthracene (DPA) using a method where both time-resolved emission and transient absorption measurements are needed. While the same method in principle is applicable to any system, the spectral overlap between the prompt fluorescence of 4CzBN and the T1 ® Tn absorption of e.g., PPO complicates matters considerably for the systems used here. A new method has instead been developed which relies solely on time-resolved emission measurements of the UC samples, thus circumventing the need for transient absorption.