High-Purity Strontium Carbonate Shows the Narrowest Peak Width of Raman Scattered Light

Raman microscopes are widely used in various fields and their spectral resolutions differ greatly depending on the system and optical components. Thus, it is important to evaluate the spectral resolution of Raman systems under measurement conditions. Although calcite is a crystal with a trigonal structure and its narrow peak at ∼1086 cm^-1 has been used to evaluate the spectral resolution of Raman spectrometers, the peak width of calcite itself, ∼1.3 cm^-1 at full width half-maximum (FWHM), is not negligible under high spectral resolution conditions. Because the calcite peak at ∼1086 cm^-1 originates from symmetric stretching, which is a common vibration mode for carbonate salts, we examined strontium carbonate (SrCO₃), barium carbonate (BaCO₃), and lead carbonate (PbCO₃) reagents to find a material having a narrower peak width than calcite. SrCO₃, BaCO₃, and PbCO₃ peaks originating from symmetric stretching were observed at 1072, 1059, and 1054 cm^-1, respectively, and their peak widths at FWHM (0.67, 0.92, and 1.09 cm^-1, respectively) were narrower than that of calcite (1.36 cm^-1). The narrow peak width of SrCO₃ was strongly dependent on its purity, probably due to its high structural regularity, and the change in the peak width (FWHM) was only 0.12 cm^-1 between 5 °C and 45 °C. Thus, we concluded that the high-purity SrCO₃ peak at 1072 cm^-1 was the narrowest peak of Raman scattering light under ambient conditions and is suitable for evaluating high spectral resolution for Raman spectrometers.