Size-dependent Photochromic And Holographic Storage Properties Of Ag/TiO₂ Nanocomposite Film

Ag/TiO₂ film can change its color from brownish-gray to the color of the incident light under visible light irradiation, and this process is reversible under UV illumination. This is because the surface plasmon resonance (SPR) absorption properties of Ag NPs with various sizes and shapes, and the effects of surrounding dielectric and physical environment on it, which made Ag NPs absorb and scatter incident lights and thus change the color of the film. Previous investigations show that the color change can be explained by the transfer of hot electrons from the Fermi level of Ag NPs to the conduction band of TiO₂, and hot electrons are caused by the collective oscillation of conduction electrons in Ag particles under incident light excitation. Ag NPs are thus ionized and change their volume, which decreases the absorption coefficient and increases the scattering coefficient of Ag particles; as a result, the color of the incident light appears. Reversible color change under UV illumination is due to the generation of electron-hole pairs, which reduces the generated Ag+ and revert the film to brownish-gray. The photochromic properties of Ag/TiO₂ can be applied to colorimetric sensor, multiwavelength optical data storage, photoconducting devices et al.To comprehensively explore the photochromic and holographic storage properties of Ag/TiO₂ film, we prepared highly transparent Ag/TiO₂ films with different Ag to Ti molar ratio by dip-coating for TiO₂ and controlling the photocatalytic reduction period of Ag+. Then, irradiation with 532 nm green laser beam was carried out to study the hole-burning effects and qualitatively analyze the photochromic rate. Ag/TiO₂ film with corresponding photochromic rate were applied in holographic storage by employing two coherent 532 nm green laser beams as record and a 633 nm red laser beam as probe. As a result, we found that the photochromic rate is closely related to Ag size distribution, mainly attributes to the size-dependent hot electron transfer efficiency from Ag to the conduction band of TiO₂, and faster photochromic rate corresponds to faster grating response in holographic storage. Besides, the present diffractive efficiency and grating response all leave something to be further improved if the microstructure of the film could be designed with more careful.