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Wavelength‐Dependent Photosensitivity in a Germanium‐Doped Sol–Gel Hybrid Material for Direct Photopatterning

Photosensitivity, as evident in permanent changes in refractive index and volume upon light exposure, is observed in a germanium‐doped methacrylate hybrid material (hybrimer) and found to depend on the wavelength of the UV light. Exposure to short‐wavelength UV illumination (220–260 nm) results in very high photosensitivity with changes in refractive index (Δn ≈ 0.0164) and film thickness (Δt ≈ –40 %) that are mainly a result of photopolymerization and Ge‐related densification. In contrast, the hybrimer is hardly photosensitive to light in the long UV‐wavelength range (350–390 nm). Direct photopatterning of a single circle on the hybrimer film creates a concave lens‐like topography upon illumination with UV light of short wavelength and a convex lens‐like one upon illumination with UV light of long wavelength.