[In situ resonance Raman spectra of organic pigments in freshwater cultured pearls].

ABSTRACT

In situ resonance Raman spectra of Chinese freshwater pearls were collected and analysed systematically with three different excitation wavelengths at lambda = 514, 633 and 785 nm. At the same time, the Raman spectra of eggshells of Pomacea canaliculata were also collected under the same experimental conditions in order to compare with pearls' Raman spectra. The conclusions were as follows (1) Frequency dispersions of Raman spectra of organic pigments were obviously observed in Raman spectra of pearls. In contrast, Raman spectra of organic pigments in eggshells of Pomacea canaliculata showed no frequency dispersion phenomena; (2) It was considered that the organic pigments in pearls were polyacetylenic materials but not carotenoids which was proposed by previous researchers, and the organic pigments in eggshells of Pomacea canaliculata were carotenoids; (3) The conjugated (>=C number of polyacetylenic material in pearls was calculated to be about 10 and 16, and the conjugated C[double bond]C number of carotenoid in eggshells of Pomacea canaliculata was about 13 based on the Raman shifts caused by conjugated C[double bond]C double bonds.