Efficient Redirection\nof Trapped Broad-Band Fluorescence\nfrom Substrates into Free Space Using c‑Si Metasurfaces

Fluorescent dye films on transparent substrates are essential\nfor\nOLEDs, flexible displays, X-ray detection, and wireless optical communications.\nHowever, their efficiency is often hampered by fluorescence trapping\ndue to total internal reflection (TIR) and waveguiding. This study\ntackles this longstanding challenge by reconceptualizing the integration\nof dye films with nanoantenna metasurfaces. Traditional methods involve\ndirectly spin-coating films onto c-Si metasurfaces on quartz substrates,\nresulting in edge luminescence and weak inner signals. We present\na straightforward, adjustable approach by integrating dye films on\nthe opposite side of quartz substrates, reaching a 2.5-fold photoluminescence\nenhancement and improving the uniformity of the emission compared\nto the conventional methods. These gains stem from redirecting a significant\nportion of leaked fluorescence light trapped inside the substrate\ninto free space, surpassing TIR conditions through in-plane diffraction\norders of the metasurfaces across the full RGB spectrum. Our findings\nfacilitate the design of more efficient luminescent devices.