CATHODOLUMINESCENCE MICROANALYSIS OF NATURAL HYDRATED AMORPHOUS SIO2 - OPAL

Natural amorphous hydrated silicon dioxide (opal) has been investigate d for the first time using Cathodoluminescence microanalysis in a Scan ning Electron Microscope. Defect centers have been identified and imag ed with high sensitivity and high spatial resolution. Intrinsic defect s identified include the non bridging oxygen hole center (NBOHC) and t he oxygen deficient centers (ODC). Impurities are strongly correlated with the grain structure of the precious opal and a higher than averag e concentration of impurity defects are observed at grain boundaries a nd cracks. Impurity associated defect centers include the NBOHC with - OH precursor, and the charge compensated substitutional Al, Ti, and Fe centers. Cathodoluminescence microanalysis provides important informa tion about the defect structure and long term stability of precious op al.