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The photo darkening phenomena in As 50 Se 50 chalcogenide thin film is studied under the influence of 532 nm laser irradiation. The optical absorption edge shifts towards lower energy side with irradiation at different interval of time. The refractive index and absorption coefficient of the film was determined, both before and after exposure, by analyzing the material's transmission spectrum. The value of the absorption coefficient of the As 50 Se 50 thin film decreases on exposing the film to laser irradiation. The change in refractive index makes the material as useful candidate for optical switching. A microscopic model in which heteropolar bonds are broken by absorption of high energy photons and new homopolar bonds are formed simultaneously has been used to describe the effect. The photo induced effects in this case were caused by heteropolar chemical bonds switching in homopolar ones, as well as additional channel of bridge heteropolar bonds switching in short-layer ones. The both processes were associated with formation of anomalously coordinated defect pairs and accompanying atomic displacements at the level of medium-range ordering. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical alternations in the bonding. The proposed model was supported by the XPS data. The films were purely amorphous in nature as revealed from X-ray diffraction and composition of the film was determined from energy dispersive X-ray analysis. [ABSTRACT FROM AUTHOR]

GeS chalcogenide amorphous film was deposited on glass substrate via PLD (pulsed laser deposition) technique. The performance and structure of the film was characterized by XRD (X-ray diffraction), SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectroscopy), optical transmission spectra, and Raman spectra, etc. The GeS amorphous film was irradiated by 532 nm linearly polarized light, and its photo-induced darkening was investigated. The results showed that the GeS chalcogenide amorphous film was smooth and compact with uniform thickness and combined with the substrate firmly, and its chemical composition was in consistency with the bulky target. When laser energy was fixed, the transparence of the film declined with the increase of the laser irradiation time. Obvious photo-induced darkening and relaxation phenomenon of the film after laser irradiation were observed in this investigation. [ABSTRACT FROM AUTHOR]

Abstract: Photoluminescence (PL) of photochromic pHEMA-TiO2 gels-based hybrids was studied by means of time- and energy-resolved spectroscopy at temperatures between 300K and 10K. The PL band at 485nm is assigned to S0←T1 transition of methoxyphenol (organic molecule added to the commercial monomer hydroxyethyl methacrylate, HEMA and used as an inhibitor of spontaneous polymerisation) in the polymer environment, while the PL band at 600nm is assigned to the self-trapped exciton onto octahedral TiO6 site of the inorganic component. The mechanisms of the excited states population are discussed. In particular it is shown that both singlet-triplet energy transfer in methoxyphenol and methoxyphenol–TiO2 charge transfer are strongly affected by the material composition and temperature. The hypothesis about the photoexcited holes annihilation with the trapped electrons is confirmed to be one of main mechanisms limiting the Ti3+ centres concentration. [Copyright &y& Elsevier]