RAMAN SPECTRA OF CRYSTALLINE DOUBLE CALCIUM ORTHOVANADATES [Ca.sub.10]M[ AND THEIR INTERPRETATION BASED ON DECONVOLUTION INTO VOIGT PROFILES

Unpolarized spontaneous Raman spectra of crystalline double calcium orthovanadates [Ca.sub.10]M[(V[O.sub.4]).sub.7] (M = Li, K, Na) in the range 150-1600 [cm.sup.-1] were measured. Two vibrational bands with full-width at half-maximum (FWHM) of 37-50 [cm.sup.-1] were found in the regions 150-500 and 700-1000 [cm.sup.-1]. The band shapes were approximated well by deconvolution into Voigt profiles. The band at 700-1000 [cm.sup.-1]was stronger and deconvoluted into eight Voigt profiles. The frequencies of two strong lines were ~848 and ~862 [cm.sup.-1]for [Ca.sub.10]Li[(V[O.sub.4]).sub.7]; ~850 and ~866 [cm.sup.-1]for [Ca.sub.10]Na[(V[O.sub.4]).sub.7]; and ~844 and ~866 [cm.sup.-1] for [Ca.sub.10]K[(V[O.sub.4]).sub.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.sup.-1]. The two strongest lines had widths of 21-25 [cm.sup.- 1]. The vibrational band at 300-500 [cm.sup.-1] was ~5-6 times weaker than that at 700-1000 [cm.sup.-1] and was deconvoluted into four lines with widths of 25-40 [cm.sup.-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.