Nanocrystalline TiO2 has been obtained by a sol-gel process by controlling the crystal size through the water/alkoxide ratio. Raman spectra of anatase nanocrystals with average sizes of 9.5–13.4 nm are reported and the correlation between the Raman band shape (peak position and linewidth) of the main feature at 144 cm−1 and the crystals dimension is discussed. While in this system a minor role is played by nonstoichiometry and pressure effects, a model based on the phonon confinement, which takes into account the size distribution as determined by the transmission electron microscopy images, correctly reproduces the Raman band shape change.

Films and powders of iron oxide (Fe 2 O 3 ) prepared by two different sol-gel syntheses, starting from Fe(NO 3 ) 3 Ð9H 2 O or FeCl 3 Ð6H 2 O, were investigated by Raman microscopy. Different phases with different morphology were produced according to the preparation. The spectra obtained in the micro-Raman configuration were compared with the ambiguous data in the literature given by conventional Raman techniques. The principal difficulty in the correct interpretation of the Raman spectrum of the iron oxides is the co-existence of different phases. Contradictory results are also explained by laser-induced thermal effects which easily change the wavenumbers and lineshapes of the phonons. A Stokes-Anti-Stokes procedure was utilized to control the local temperature during the measurement and also for calibration of the wavenumbers. The micro-Raman spectra of hematite, magnetite and other iron oxides are presented and compared with literature data.

Synthetic and natural spinel single crystals having compositions closely approaching spinel end-members ZnCr2O4, MgCr2O4, FeCr2O4, ZnAl2O4, MgAl2O4, CoAl2O4, FeAl2O4, MnAl2O4, MgFe2O4, and FeFe2O4 were investigated by Raman spectroscopy in the 100-900cm-1 range using both the red 632.8nm line of a He-Ne laser and the blue 473.1nm line of a solid-state Nd:YAG laser. Each end-member exhibits a Raman fingerprint with at least one peculiar peak in terms of Raman shift and relative intensity. Chromates and ferrites exhibit the most intense A1g mode at around 680cm-1, at lower wavenumbers than in the aluminates, in agreement with the heavier atomic mass of Cr and Fe with respect to Al. For aluminate spinels, the most intense and diagnostic peaks in the spectrum are as follows: F2g(1) at 202cm-1 for MnAl2O4, Eg at 408cm-1 for MgAl2O4, F2g(2) at 516cm-1 for CoAl2O4, F2g(3) at 661cm-1 for ZnAl2O4, and A1g at 748cm-1 for FeAl2O4. Noteworthy, analyzing the A1g, F2g(3), and, in particular, the Eg peak positions, it is possible to establish which subgroup a spinel belongs to; moreover, a careful inspection of both position and relative intensity of the same peaks allows the determination of the end-member type

Green earths' are employed since antiquity as pigments in the creation of artworks. The minerals responsible for the colour belong to four groups: (1) the clayey micas celadonite and glauconite, undoubtedly the most common; (2) smectites; (3) chlorites; (4) serpentines. Whereas there have been several studies on clayey materials, mineralogical analyses in the field of cultural heritage are mainly limited to the identification of the green earth without specific characterization of the mineralogical species. This work shows a preliminary characterization by the multi-techniques approach of some raw minerals (glauconite, celadonite and ferroceladonite). Vibrational analyses have been correlated with elemental analyses, thanks to the hyphenated instrumentation of scanning electron microscopy with EDS and Raman structural and chemical analyser (SEM-EDS-SCA) probes, which permitted collection of EDS and Raman spectra on the same microscopic area. Micro-Raman and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopieswere able to distinguish between celadonite and glauconite. The use of different lasers revealed resonance effects in the Raman spectra. In addition to pure minerals, archaeological samples and commercial green earths were also analysed, thereby enabling a more precise classification of the green pigments in heterogeneous samples such as wall paintings. Some commercially available green earths were found to contain organic dyes.

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