Health & Environmental Research Online (HERO)


Print Feedback Export to File
8050861 
Journal Article 
Are the rates of dexter transfer in TADF hyperfluorescence systems optically accessible? 
Haase, N; Danos, A; Pflumm, C; Stachelek, P; Bruetting, W; Monkman, AP 
2021 
8 
6 
1805-1815 
English 
34846509 
WOS:000641058400001 
Seemingly not, but for unexpected reasons. Combining the triplet harvesting properties of TADF materials with the fast emission rates and colour purity of fluorescent emitters is attractive for developing high performance OLEDs. In this "hyperfluorescence" approach, triplet excitons are converted to singlets on the TADF material and transferred to the fluorescent material by long range Förster energy transfer. The primary loss mechanism is assumed to be Dexter energy transfer from the TADF triplet to the non-emissive triplet of the fluorescent emitter. Here we use optical spectroscopy to investigate energy transfer in representative emissive layers. Despite observing kinetics that at first appear consistent with Dexter quenching of the TADF triplet state, transient absorption, photoluminescence quantum yields, and comparison to phosphor-sensitised "hyperphosphorescent" systems reveal that this is not the case. While Dexter quenching by the fluorescent emitter is likely still a key loss mechanism in devices, we demonstrate that - despite initial appearances - it is inoperative under optical excitation. These results reveal a deep limitation of optical spectroscopy in characterizing hyperfluorescent systems.