Thickness-Dependent Thermo-Optical Response in Micro/Nanostructured Bioglass Films

Bioglass (BG) thin films are promising materials for integrating bioactivity with dynamically tunable optical functionality. Here, BG coatings containing two, four, and six deposited layers were fabricated by spin coating to investigate how deposition-dependent changes in thickness and micro/nanostructural organization relate to the thermo-optical response. Film thicknesses were estimated to be 348, 667, and 1061 nm for BG2, BG4, and BG6, respectively. SEM analysis revealed exposed nanorod-like structures in BG2, whereas increasing the number of layers produced thicker and more consolidated porous architectures. The thermo-optical modulation was experimentally investigated using a cross-polarized transmission setup with a 1064 nm pump beam. All samples displayed comparable photothermal dynamics over the investigated irradiance range. However, their optical modulation showed different temperature dependences, with quadratic trends for BG2 and BG4 and an approximately linear trend for BG6. Differences between optical and thermal dynamics can be associated with nonlinear polarization-sensitive detection, thermal gradients, and thermoelastic or scattering contributions. These results suggest that nanostructured domains, porous morphology, and film–substrate interfaces influence the thermo-optical modulation of BG films. The findings motivate further investigation of these coatings for potential biotechnological photonic applications.