Fabrication and Characterization of Angle-Independent Structurally Colored Films Based on CdS@SiO₂ Nanospheres

It is easy for chemical pigments produced from organic chemicals to disappear when exposed to light over time. Recently, structurally colored pigments produced by materials with high indices of refraction such as TiO₂ or ZnS have attracted great attention. This study presents that CdS@SiO₂ core-shell nanospheres were synthesized through a homogeneous deposition method followed with a modified Stöber method and a calcination process. Colored film assembled by pigments shows low angle dependence with high stability against degradation under environmental factors. Moreover, the structural color of CdS@SiO₂ arrays was bright and tunable according to the size without changing the overall material design. Compared with the conventional method, the addition of black substances in colloidal spheres is the generally used method to realize angle-independent structural coloration. However, black materials (such as carbon blacks and acetylene black) are not stable because of the high surface energy, and usually reunite together easily, and then lead to a nonuniform distribution and significant decrease in brightness. Thus, we report self-assembly colored films with great low angle dependence but not any black substances. Moreover, the refractive index of CdS is higher than generally used PS, PMMA, and SiO₂, and the SiO₂ shell is poisonless. CdS@SiO₂ structurally colored films have promising nonbleaching pigments and have potential applications for displays, colorimetric sensors, colorful decoration, and pigments.