A Ceramic Photonic Crystal Temperature Sensor

Photonic bandgap effects are observed in a disordered array of sol‐gel‐derived SiO 2 particles prepared via centrifugation of a colloidal suspension. Tunability in the optical response is achieved by infiltrating an organic liquid (1‐methylnaphthalene) that possesses a moderately high temperature coefficient of refractive index (d n /d T ) into the interparticle void space. The varying d n /d T value between SiO 2 and 1‐methylnaphthalene is used to tune the contrast ratio, relative to temperature. The resulting optical temperature sensor is the first adaptive ceramic photonic crystal of its type, to our knowledge, and provides a proof‐of‐concept for simple, disposable optical devices that are based on photonic band engineering. Novel applications of optical structures that possess short‐range particulate order are discussed, in consideration of the direct analogy between photonic bandgaps and X‐ray diffraction.