Photo- and Thermobleaching of Luminescence Centers in Synthetic Opals

It has been found that on exposure of specimens of synthetic opal to UV radiation, luminescence is excited in them (337 nm) that has spectral maxima at 400 and 500 nm. Its duration at half-height of a pulse is 9 nsec, and there is a weak slow component with τ ∼ 1 μsec. The spectrum and intensity of the luminescence depend on the duration of irradiation and temperature. The luminescence bands revealed relate to two individual luminescence centers, namely: the shortwave one, caused by the luminescence centers formed in the bulk of the opal, and the longwave one, due to those formed on the opal surface.