Reversible Shift from Excitonic to Excimer Emission in Fluorescent Organic Light-Emitting Diodes: Dependence on Deposition Parameters and Electrical Bias

Abstract

Organic light-emitting diodes (OLEDs), in general, require multilayer devices and microcavity structures for emission tuning, which increases the complexity and cost of production. Hence, it is imperative to develop techniques for spectral tuning, which employ simplified device structures. In this study, we have selected a tris(8-hydroxyquinolinato)aluminum (Alq 3 ): 10-(2benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)benzopyropyrano (6,7-8-i,j)quinolizin-11-one (C545T)-based OLED and investigated the dependence of the OLED emission on various deposition parameters and the electrical bias. The concentration of the dopant in the emissive layer (EML) was varied from 3 to 50%, and the single dopant emitter as a limiting case was also studied along with studies on the varied deposition rates and EML thickness. By varying the deposition parameters, the emission was observed to change from excitonic green to excimeric yellow. With increased doping concentration, reduction in pure exciton emission with an increase in excimer emission was observed, resulting in electroluminescent spectral red shift. Similarly, electroluminescence spectra have shown different levels of broadening, depending on the deposition rate and thickness of the EML. These effects could be reversed with increasing applied electric field. Thus, it is indicated that, by suitably optimizing the deposition parameters of the dopant material, spectral tuning can easily be obtained, which may form the basis of simplified and cost-effective device structures.

Improving Photophysical Properties of White Emitting Ternary Conjugated Polymer Blend Thin Film via Additions of TiO2 Nanoparticles

“…These reductions are likely due to the exciplexes (heterodimerics) creation at high acceptor concentration [ 19 ]. Besides, it could also be due to the active self-quenching in the blends resulting from the creation of excimers (homodimers) between acceptor monomers [ 29 ] which then converted into heat. Nonetheless, the current work successfully proves that the emission characteristics of the PFO/F8BT/MEH-PPV ternary blend can be properly tuned by carefully controlling the F8BT content.…”

Controlling the Emission Spectrum of Binary Emitting Polymer Hybrids by a Systematic Doping Strategy via Förster Resonance Energy Transfer for White Emission

“…These quenching can be attributed to the heterodimerics (exciplexes) formation at a high acceptor content [27]. On the other hand, the quenching can also be attributed to the active self-quenching in the hybrids, resulting from the formation of homodimers (excimers) between monomers of the acceptor [28] that are then converted to heat.…”

Device parameter to evaluate exciton energy transfer in organic whispering-gallery-mode microresonators and its dependence on the amplified spontaneous emission threshold

“…When the thickness was 30 nm, the PL peak appeared at λ = 580 nm, which originates from the excimer emission. 34 For the much thinner films, the PL bands were in the much shorter wavelength region. For a thickness of 1 nm, which was the same as that used for the microresonators, the PL peak appeared at approximately λ = 515 nm.…”