Investigation of optical properties of three dimensional reflectance rulers fabricated by size-controlled monodisperse polystyrene colloidal particles.

This study is relevant to the design of the final activity of 3 dimensional photonic crystals (3D PCs), especially for applications where the reflectance range is a key parameter. Highly monodisperse spherical Polystyrene (PS) particles, synthesized in the size range of ∼200 to 550 nm by varying the concentration of Sodium Dodecyl Sulfate (SDS), are used to fabricate 3D PCs on glass substrates. The resulting structures show a clear size-dependent optical response due to their photonic crystal lattices, with reflectance values exceeding 80% across various particle sizes. This finding implies the successful fabrication of stable and homogeneous colored opal films with highly reproducible, sensitive, and tunable reflectance responses across a wide range of the visible spectrum. This set of samples can potentially serve in various applications, justifying their designation as reflectance rulers. In the following, the optical properties of the resulting PCs as reflectance rulers have been investigated by comparing simulated and experimental reflectance spectra. Interestingly, the sphere sizes estimated via Bragg's law closely match those measured using Field Emission Scanning Electron Microscopy (FESEM), validating both the substrate fabrication method and the simulation model. This consistency between the simulation predictions and the experimental observations confirms the accuracy of the assumptions used for the crystal structure.