Raman studies were performed on titania thin films prepared by polyethylene glycol (PEG) assisted, low-temperature, sol-gel method. The Raman spectra of the films show a systematic blue shift in the peak position and a broadening in the full width at half-maximum (FWHM) when compared with those of the bulk anatase TiO 2 powder. Several reports have appeared indicating this kind of peak shift and broadening of FWHM, which were attributed to the confinement of phonons in the anatase nanocrystallites. In this paper, we report an analysis of quantum size effect in the Raman spectra of nanocrystalline TiO 2 thin films performed by utilizing the phonon dispersion relation of the anatase phase which has been obtained from a work based on density functional perturbation theory (DFPT). For comparison purposes the quantum size effect calculations have also been done utilizing the dispersion relations of the rutile phase. There is good agreement between the crystallite sizes evaluated from the equally weighted Raman line intensity of the dispersion relations obtained from the DFPT and those determined by X-ray diffraction.

Macroporous hexagonal WO 3 (h-WO 3 ) films were obtained at 400 °C from a sol containing tungstic acid with organically modified silane as a template. Asymmetric electrochromic devices based on the macroporous h-WO 3 layer were constructed. XRD and micro-Raman studies of the intercalation/ deintercalation of lithium into the h-WO 3 layer of the device as a function of the applied voltages were performed. In h-WO 3 , Li + can be intercalated into three potential sites: trigonal cavity (TC), hexagonal window (HW), and four-coordinated square window (SW). XRD measurements show systematic changes in the lattice parameter, which was associated with the amount of Li intercalated into the h-WO 3 layer. Correspondingly, Raman spectroscopy shows that at 1.0 V Li + completely fill TC and partially fill HW sites. For potentials g1.5 V, Li + are inserted into the SW, as evidenced from the vanishing of the ν(O-W-O) Raman modes. The reversible characteristics of the device from optical measurements and Raman spectra demonstrated that the coloration process in the electrochromic device is mainly due to the Li + that occupy HW and SW sites of the h-WO 3 . Optical measurements performed as a function of applied potentials, show excellent contrasts between colored and bleached states and qualifies the macroporous h-WO 3 -based device for smart window applications.

Tungsten trioxide (WO3) nanostructures were synthesized by hydrothermal method using sodium tungstate (Na2WO4·2H2O) alone as starting material, and sodium tungstate in presence of ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] or cobalt chloride (CoCl2·6H2O) as structure-directing agents. Orthorhombic WO3having a rectangular slab-like morphology was obtained when Na2WO4·2H2O was used alone. When ferrous ammonium sulfate and cobalt chloride were added to sodium tungstate, hexagonal WO3nanowire clusters and hexagonal WO3nanorods were obtained, respectively. The crystal structure and orientation of the synthesized products were studied by X-ray diffraction (XRD), micro-Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM), and their chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). The optical properties of the synthesized products were verified by UV–Vis and photoluminescence studies. A photodegradation study on Procion Red MX 5B was also carried out, showing that the hexagonal WO3nanowire clusters had the highest photodegradation efficiency.

Porous orthorhombic tungsten oxide (o-WO 3 ) thin films, stabilized by nanocrystalline anatase TiO 2 , are obtained by a sol-gel based two stage dip coating method and subsequent annealing at 600 C. An Organically Modified Silicate (ORMOSIL) based templating strategy is adopted to achieve porosity. An asymmetric electrochromic device is constructed based on this porous o-WO 3 layer. The intercalation/deintercalation of lithium ions into/from the o-WO 3 layer of the device as a function of applied coloration/bleaching voltages have been studied. XRD measurements show systematic changes in the lattice parameters associated with structural phase transitions from o-WO 3 to tetragonal Li x WO 3 (t-Li x WO 3 ) and a tendency to form cubic Li x WO 3 (c-Li x WO 3 ). These phase transitions, induced by the Li ions, are reversible, and the specific phase obtained depends on the quantity of intercalated/ deintercalated Li. Raman spectroscopy data show the formation of t-Li x WO 3 for an applied potential of 1.0 V and the tendency of the system to transform to c-Li x WO 3 for higher coloration potentials. Optical measurements show excellent contrasts between colored and bleached states. An alternate photochromic device was constructed by sensitizing the o-WO 3 layer with a ruthenium based dye. The nanocrystalline anatase TiO 2 in the o-WO 3 layer has led to an enhanced photochromic optical transmittance contrast of $51% in the near IR region. The combination of the photochromic and electrochromic properties of the synthesised o-WO 3 layer stabilized by nanocrystalline anatase TiO 2 opens up new vista for its application in energysaving smart windows.