Real-time investigations of structural and optical changes in photochromic Ag/TiO2 nanocomposite thin films under laser irradiation

Photochromic reaction dynamics in silver nanoparticles embedded inmesoporous titaniumdioxide thinfilms is investigated by combining real-time grazing incidence small-angle x-ray scattering (GISAXS) and optical transmissionmeasurements duringUV–visible laser exposure cycles.While GISAXS probes changes in the particle size distribution, transmittancemeasurements are sensitive to spectral changes induced by photo-activated processes. Our results reveal a repeatable photochromic behavior with a good correlation in terms of kinetics between themorphological and optical fluctuations. Visible laser irradiation at 532 nm induces a preferential photo-dissolution of small silver particles, which in turn causes an increase in transmittance near the excitationwavelength. Furthermore, the photo-dissolution process can be significantly accelerated and amplified by associating visible laser with x-ray irradiation. UnderUV laser irradiation at 360 nm, the bleaching process can be reverted by photocatalytic reductionwith themesopores in the TiO2film acting as molds, which have the ability to confine the nanoparticle growth.However, in the irradiation conditions used in the present study, it appears that the photocatalytic growth of silver nanoparticles is slower than the photo-dissolution process, whereas its efficiency gradually degrades throughout the exposures toUV light.