Directional emission of plastic luminescent films using photonic crystals fabricated by soft-X-ray interference lithography and reactive ion etching

In this report, a novel method to prepare photonic crystals based on the combination of soft-X-ray interference lithography (XIL) and reactive ion etching (RIE) with a bi-layer photoresist system was developed. XIL can be utilized to prepare periodic structures with high efficiency but the depth of etch is limited due to the strong absorption of photoresist for soft-X-ray. Based on the pattern prepared by XIL, RIE can be utilized to further etch a second layer of photoresist, so that one can obtain a large depth of etch. Controlling the dispersion relation of the prepared photonic crystals, strongly directional emission of plastic luminescent films was demonstrated. A wavelength-integrated enhancement of 2.64-folds enhancement in the range of 420 to 440 nm in the normal direction was obtained. Guided-mode resonance and Fabry-Perot resonance could be the critical factors to control the directional emission. Devices based on directional emission films have a variety of applications in such as detectors, optical communication and display screens.