In a recent publication, Kovats and Hill ascribe Raman bands at 1575 cm−1 and 1375 cm−1 for various molybdates as being "... related to the presence of an electron donor level which can inelastically scatter light during an electronic transition." They go to great lengths to show that their data are consistent with this interpretation.
R. M. Irwin and T. B. Malloy, "An Alternative Interpretation of Some of the Spectra in "Raman Spectroscopy of Bulk Bismuth Molybdate Catalysts"," Appl. Spectrosc. 42, 179-180 (1988)