The Origin of a 650 nm Photoluminescence Band in Rubrene

Abstract

Commonly observed variations in photoluminescence (PL) spectra of crystalline organic semiconductors, including the appearance or enhancement of certain PL bands, are shown to originate from a small amount of structural disorder (e.g., amorphous inclusions embedded in a crystal), rather than be necessarily related to chemical impurities or material oxidation. For instance, in rubrene, a minute amount of such disorder can lead to the appearance of a dominant PL band at 650 nm as a result of triplet excitons captured and fused at these sites, with a subsequent emission from the amorphous phase.

Visualization of exciton transport in ordered and disordered molecular solids

“…4). Such low energy emission has also been identified in rubrene, and in that work it is similarly attributed to the presence of structural defects that act as exciton traps 35 .…”

Fluorescence from rubrene single crystals: Interplay of singlet fission and energy trapping

“…Krellner et al 23 experimentally studied the location of the oxygen-related hole trap state at 0.27 eV above the valence band. However, Podzorov et al 12 claim the 650 nm fluorescence band is emitted by amorphous rubrene molecules instead of oxidized rubrene. Therefore, our results agree with the studies by Mitrofanov and Krellner that the formation of the 650 nm band is related to the oxygen-induced trap state.…”

“…The fluorescence spectrum centered at 610 nm is usually considered as the fluorescence spectra from pristine rubrene. 12 (3) 650 nm type. Another type of fluorescence spectrum under b polarized excitation is centered at around 650 nm.…”

“…It is disputed to be due to either the oxidation related defects, 10 the band gap states, 13 or the amorphous phase embedded in the crystal. 12 In this work, we discuss the origin of the steady-state fluorescence in rubrene single crystals by stating the important role of singlet fission and energy trapping. The fluorescence kinetics observed was on a picosecond time scale due to the quenching by singlet fission.…”

Heterostructures based on inorganic and organic van der Waals systems

“…The rubrene film grown on hBN showed the main PL peak at ∼615 nm and the broad shoulder around 650 nm, similar with those of a free-standing single crystal separately prepared. 25 High-quality organic crystalline films on dielectric materials are useful for the fabrication of high-performance organic field effect transistors (FETs). In particular, a vdW dielectric such as hBN is more desirable because it forms a very clean channel-dielectric interface.…”