Abstract
Angle-resolved photoluminescence spectroscopy is a powerful tool for investigation of the properties of light-emitting thin-film structures. For instance, it can reveal information about the orientation of the transition dipole moment in organic emission layers, which is one of the most important parameters defining the efficiency of organic light-emitting diodes. In this work, a refinement of one of the main experimental configurations utilized for such orientation measurements is presented. The technique is based on a step-by-step rotation of the optically excited layer with respect to the detector. By attaching the sample to a large glass half cylinder, the light initially trapped in the substrate can be extracted. It is shown that by inserting two additional optical lenses between the half cylinder and the detector, the signal-to-noise ratio can be improved by about one order of magnitude. A ray-optics model is derived that describes the light propagation in the macroscopic setup and enables us to characterize the impact of deviations from theoretical ideal measurement configurations. The numerical predictions are experimentally validated analyzing quantum-dot emission layers as an isotropic reference and established organic emitter molecules with well-known orientation values.
Highlights
Angle-resolved photoluminescence spectroscopy (ARPS) is a fundamental technique used to study the properties and effects of light-emitting thin-film structures
We focus on ARPS configurations that are capable of measuring the angular-emission pattern inside the substrate, since this ability is required for the application case discussed later on, which is the determination of emitter molecule orientations
As second main contribution of this work, we introduce a refinement of the state-of-the-art measurement configuration yielding an about one-order-of-magnitude higher signal-to-noise ratio (SNR)
Summary
Angle-resolved photoluminescence spectroscopy (ARPS) is a fundamental technique used to study the properties and effects of light-emitting thin-film structures. Another research topic utilizing ARPS is the investigation of the position and orientation of light-emitting molecules in organic thin films In this case, the angular-intensity distribution is defined by the interference of light waves reflected multiple times at the sample interfaces. We focus on ARPS configurations that are capable of measuring the angular-emission pattern inside the substrate, since this ability is required for the application case discussed later on, which is the determination of emitter molecule orientations. As second main contribution of this work, we introduce a refinement of the state-of-the-art measurement configuration yielding an about one-order-of-magnitude higher signal-to-noise ratio (SNR) This enables us to address weakly emitting and fast-degrading materials. As experimental validation, the orientation of organic emitter molecules and quantum dots is determined with both the conventional and the refined setup, resulting in consistent values
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