| Abstract
| - The visible (532 and 442 nm) and UV (325 nm) Raman spectra of bulk mixed metal oxides (metal molybdatesand metal vanadates) were compared on the same spectrometer, forthefirsttime, to allow examination ofhow varying the excitation energy from visible to UV affects the resulting Raman spectra. The quality of theRaman spectra was found to be a strong function of the absorption properties of the bulk mixed oxide. Forbulk mixed metal oxides that absorb weakly in the visible and UV regions, both the visible and UV Ramanspectra were of high quality and exhibit identical vibrational bands, but with slightly different relative intensities.For bulk mixed metal oxides that absorb strongly in the UV and visible regions and/or strongly in the UVand weakly in the visible regions, the visible Raman spectra are much richer in structural information and ofhigher resolution than the corresponding UV Raman spectra. This is a consequence of the strong UV absorptionthat significantly reduces the sampling volume and number of scatterers giving rise to the Raman signal. Theshallower escape depth of UV Raman, however, was not sufficient to detect vibrations from the surfacemetal oxide species that are present on the outermost surface layer of these crystalline mixed metal oxidephases as previously suggested. It was also demonstrated that there is no sample damage by the more energeticUV excitation when very low laser powers and fast detectors are employed, thus avoiding the need ofcomplicated fluidized bed sample arrangements sometimes used for UV Raman investigations. The currentcomparative Raman investigation carefully documents, forthefirsttime, the advantages and disadvantagesof applying different excitation energies in collecting Raman spectra of bulkmixedmetaloxidematerials.
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