Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters

TL;DR

This paper investigates the exciton dynamics in organic biluminescent emitters, revealing how singlet-triplet interactions affect efficiency and providing insights into excitonic effects in organic materials.

Contribution

It presents a detailed study of exciton lifetimes and interactions in biluminescent emitters, highlighting the impact on efficiency and offering a model for excitonic effects analysis.

Findings

Triplet and singlet exciton lifetimes range from 3 ns to 300 ms.

Singlet-triplet annihilation reduces biluminescence efficiency.

Oxygen quenching controls triplet exciton density over several orders of magnitude.

Abstract

Biluminescent organic emitters show simultaneous fluorescence and phosphorescence at room temperature. So far, the optimization of the room temperature phosphorescence (RTP) in these materials has drawn the attention of research. However, the continuous wave operation of these emitters will consequently turn them into systems with vastly imbalanced singlet and triplet populations, which is due to the respective excited state lifetimes. This study reports on the exciton dynamics of the biluminophore NPB (N,N-di(1-naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine). In the extreme case, the singlet and triplet exciton lifetimes stretch from 3 ns to 300 ms, respectively. Through sample engineering and oxygen quenching experiments, the triplet exciton density can be controlled over several orders of magnitude allowing to studying exciton interactions between singlet and triplet manifolds. The results show, that singlet-triplet annihilation reduces the overall biluminescence efficiency already at moderate excitation levels. Additionally, the presented system represents an illustrative role model to study excitonic effects in organic materials.