Raman Spectra of Crystalline Double Calcium Orthovanadates Ca10M(VO4)7 (M = Li, K, Na) and Their Interpretation Based on Deconvolution Into Voigt Profiles

Abstract

Unpolarized spontaneous Raman spectra of crystalline double calcium orthovanadates Ca10M(VO4)7 (M = Li, K, Na) in the range 150–1600 cm–1 were measured. Two vibrational bands with full-width at half-maximum (FWHM) of 37–50 cm–1 were found in the regions 150–500 and 700–1000 cm–1. The band shapes were approximated well by deconvolution into Voigt profiles. The band at 700–1000 cm–1 was stronger and deconvoluted into eight Voigt profiles. The frequencies of two strong lines were ~848 and ~862 cm–1 for Ca10Li(VO4)7; ~850 and ~866 cm–1 for Ca10Na(VO4)7; and ~844 and ~866 cm–1 for Ca10K(VO4)7. The Lorentzian width parameters of these lines in the Voigt profiles were ~5 times greater than those of the Gaussian width parameters. The FWHM of the Voigt profiles were ~18–42 cm–1. The two strongest lines had widths of 21–25 cm–1. The vibrational band at 300–500 cm–1 was ~5–6 times weaker than that at 700–1000 cm–1 and was deconvoluted into four lines with widths of 25–40 cm–1. The large FWHM of the Raman lines indicated that the crystal structures were disordered. These crystals could be of interest for Raman conversion of pico- and femtosecond laser pulses because of the intense vibrations with large FWHM in the Raman spectra.