Gelled colloidal crystals as tunable optical filters for spectrophotometers

We examined the performance of charged colloidal crystals immobilized in a polymer gel as tunable optical filters. The colloidal crystals of charged silica particles (particle diameter = 121 nm; particle concentration = 3.5vol%; and Bragg wavelength lambda(B) = 630-720 nm) were produced by unidirectional crystallization under a temperature gradient. Photocurable gelation reagents were dissolved in the sample beforehand; this enabled gel immobilization of the crystals under ultraviolet illumination. The crystals had dimensions of more than 25 mm(2) in area and 1 mm in thickness, and spatial lambda(B) variations of less than 1%. Upon mechanical compression, lambda(B) values shifted linearly and reversibly over almost the entire visible spectrum. Using the gelled crystals as tunable optical filters, we measured the transmittance spectra of various samples and found them to be in close agreement with those determined using a spectrophotometer equipped with optical gratings. (C) 2016 The Japan Society of Applied Physics