CL emission in barite affected by lead

Abstract:

Cathodoluminescence (CL) is emission of light induced by electron beam. The properties of CL, such as colors, intensities and spectral-peaks, depend on the impurities in the material and structural defects inherent in the crystal. In the previous studies with radioluminescence(RL), and X-ray luminescence, lead was found to be one of the emission centers of Barite[１]. In the present study, we investigated the relationship between the concentration of lead and the CL intensity in barite.

25 natural Barite from various areas and synthetic barite with 10 levels of lead concentrations, were examined in the present study. Lead doped barite samples were synthesized by mixing solutions of barium nitrate (Ba(NO₃)₂) with appropriate amount of lead nitrate (Pb(NO₃)₂), and sodium sulfate (Na₂SO₄). SEM-CL analysis was conducted using a SEM (JEOL: JSM-5410) combined with a grating monochromator (Oxford: Mono CL2) in the range from 300 to 800 nm in 1 nm steps. The wavelength dependent photomultiplier response was calibrated with a standard light source to have correct CL spectra.

As a result of spectral analysis with deconvolution, a blue, broad band emission was identified around 350~400 nm (UV-blue region) in some natural and synthetic samples.

With EPMA and MA-ICP-MS analysis, the natural samples showing CL were found to have lead at maximum of 27.8 wt%.

When plotting the blue CL intensities against the lead concentrations in natural samples, the CL is proportional up to 5000ppm to lead concentration while concentration quenching would happen in samples with higher concentrations. A similar trend was also observed in synthetic barite samples.

[１]Gaft, M. L. et al (1985) Luminescence Centers in Anhydrite, Barite, Celestite and Their Synthesized Analogs, Phys and Chemistry of minerals, 11, 255-260.