Tunable high-index photonic glasses

Lukas Schertel, Ilona Wimmer, Patricia Besirske, Christof M. Aegerter, Georg Maret, Sebastian Polarz and Geoffroy J. Aubry PHYSICAL REVIEW MATERIALS 3, 015203 (2019) DOI: 10.1103/PhysRevMaterials.3.015203

Abstract: Materials with extreme photonic properties such as maximum diffuse reflectance, high albedo, or tunableband gaps are essential in many current and future photonic devices and coatings. While photonic crystals, periodic anisotropic structures, are well established, their disordered counterparts, photonic glasses (PGs), areless understood despite their most interesting isotropic photonic properties. Here, we introduce a controlled highindex model PG system. It is made of monodisperse spherical TiO2 colloids to exploit strongly resonant Miescattering for optimal turbidity. We report spectrally resolved combined measurements of turbidity and lightenergy velocity from large monolithic crack-free samples. This material class reveals pronounced resonancesenabled by the possibility to tune both the refractive index of the extremely low polydisperse constituents andtheir radius. All our results are rationalized by a model based on the energy coherent potential approximation,which is free of any fitting parameter. Surprisingly good quantitative agreement is found even at high index andelevated packing fraction. This class of PGs may be the key to optimized tunable photonic materials and alsocentral to understand fundamental questions such as isotropic structural colors, random lasing or strong lightlocalization in 3D.