This paper presents a study of the light output characteristics of laterally emitting thin-film electroluminescent (LETFEL) devices. The limitations of the conventional non-etched LETFEL outcoupling mechanism have been theoretically and experimentally analysed. The theoretical approach assumes the device behaves as a perfect optical waveguide and studies the scattering and bend radiation losses responsible for outcoupling at the aperture locations. This study leads to outcoupling efficiency values under 2%. Additionally, the angular profile has been experimentally determined and illustrates two maxima at ±50 • . As a result, we conclude that the conventional non-etched LETFEL output characteristics are not optimum for the two main LETFEL applications, which are head mounted displays (HMD) and electrophotographic printing (EP). Consequently, an alternative outcoupling mechanism is introduced, which is referred to as the etched LETFEL device. This has been fabricated for the first time, using ion milling. The resultant light output characteristics have been experimentally determined and subsequently compared with the conventional non-etched structure properties. A 400% enhancement in the total emitted light intensity has been obtained for a 600 V peak to peak driving voltage, using the etched structure. Additionally, the angular profile is observed to redistribute towards narrower angles of view. This introduces further enhancement of the coupling efficiency of HMD and EP applications, with acceptance angles under 30 and 6 • respectively, by 12 and 5% respectively.
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