Comparison among Termoluminescente Emission Specters and Photoinduced Emission of the Topaz

Abstract

Topaz has shown to be useful for dosimetric application. This mineral presents a satisfactory thermoluminescence (TL) response to radiation. In previous work we analysed the natural topaz samples from Minas Gerais, Brazil, by TL, infrared and X-ray diffraction techniques with the aim of obtain an explanatory model for the process of light emission of this mineral. Thermal treatments and irradiations do not produce significant alterations in the TL emission. TL spectra present a broad band with one of the maximum of TL intensity at 420 nm in all the samples. The wavelengths of the light emitted from the topaz are similar at the silicates; so that, the luminescence centres of the topaz samples should be the same at the silicates, centers [AlO4]0 and [H3O4]0, and there is a close relationship between the [OH]/[F] concentration ratio and the intensity of the TL glow curves. Aiming to understand the physical processes involved in the light emission of the topaz we analysed the photoinduced fluorescence of the natural (as received) and thermally treated samples in the powder form. The emission spectra were performed with a fluorimeter in the range of 300 to 800 nm, with a slit width of 2 mm in the excitation and 1 mm in the housings. The photoinduced emission of the topaz has been similar to other silicates. In range of the UVvisible, there are intense emission bands between 350 and 550 nm. The intensities are different to each sample. The sample with larger photoinduced emission intensity was the topaz 2, as well as in the TL analyses. The ratio between the areas of the two main bands of the photoinduced emission spectra were altered after the samples have been thermally treated.