[SCG55-P11] Spectral Analysis of Cathodoluminescence of Barite
キーワード：重晶石、カソードルミネッセンス、発光メカニズム
Cathodoluminescence (CL), luminescence following electron excitation, in minerals varies in emission color, intensity, and spectrum, gives information on impurity compositions and structural lattice defects. In the present study, CL of barite (BaSO4) was investigated, which had not been studied in detail. Although CL in many minerals has similarity with photoluminescence (PL), excited by UV, and radioluminescence (RL), excited by X-rays, it was found that barite is not the case.
Twenty-five natural barite samples, which show PL of various colors, were examined in the present study. SEM-CL analysis was conducted using an SEM (JEOL: JSM-5410) combined with a grating monochromator (Oxford: Mono CL2) in the range from 300 to 800 nm in 1 nm steps with a temperature-controlled stage from -190 to 25 ℃. The wavelength dependent photomultiplier response was corrected with a standard light source to have correct CL spectra. They were then converted to the ones according to photon energy in eV and then deconvoluted into Gaussian components with using OriginPro 9J.
Color CL images with blue emissions were obtained only from five samples while other samples show no CL, although most samples examined here exhibit various luminescent colors of blue, beige, yellow, white and magenta under a UV lamp.
As the result of the spectral analysis with deconvolution, the spectra with the strong and weak blue emissions have a broad band around 370 nm in UV-blue region, but no clear emission in red region. In previous studies, luminescence peaks were reported due to an intrinsic center of SO42- and to an impurity center of Pb-ion or Eu-ion [1,2]. The peak position of the present result was found to be close to these previous studies.
With EPMA and LA-ICP-MS analysis, Pb contents were obtained in the samples. It was found that those with Pb content of 23.8 wt% or more show strong CL and that those with 500 ppm or less show weak CL, while those with no CL do not contain any impurity elements. The temperature-controlled CL measurements reveled that the peak position of blue CL of strong emission (hence larger Pb content) did not change with temperature, whereas the emission intensity of the sample, containing Pb of 0.5 wt% or less, increase with temperature.
Therefore, the blue CL emissions found in barite might be composed of an impurity center of Pb-ion activator or sensitizer, and the 3.28 eV component may be composed of SO42-defect centers.
[1] Marshall, J. (1988) Cathodoluminescence of geological materials, Unwin Hyman, 1-146.
[2] Hirotsugu, N. et al. (2004) Temperature effect on cathodoluminescence of anhydrite.
Twenty-five natural barite samples, which show PL of various colors, were examined in the present study. SEM-CL analysis was conducted using an SEM (JEOL: JSM-5410) combined with a grating monochromator (Oxford: Mono CL2) in the range from 300 to 800 nm in 1 nm steps with a temperature-controlled stage from -190 to 25 ℃. The wavelength dependent photomultiplier response was corrected with a standard light source to have correct CL spectra. They were then converted to the ones according to photon energy in eV and then deconvoluted into Gaussian components with using OriginPro 9J.
Color CL images with blue emissions were obtained only from five samples while other samples show no CL, although most samples examined here exhibit various luminescent colors of blue, beige, yellow, white and magenta under a UV lamp.
As the result of the spectral analysis with deconvolution, the spectra with the strong and weak blue emissions have a broad band around 370 nm in UV-blue region, but no clear emission in red region. In previous studies, luminescence peaks were reported due to an intrinsic center of SO42- and to an impurity center of Pb-ion or Eu-ion [1,2]. The peak position of the present result was found to be close to these previous studies.
With EPMA and LA-ICP-MS analysis, Pb contents were obtained in the samples. It was found that those with Pb content of 23.8 wt% or more show strong CL and that those with 500 ppm or less show weak CL, while those with no CL do not contain any impurity elements. The temperature-controlled CL measurements reveled that the peak position of blue CL of strong emission (hence larger Pb content) did not change with temperature, whereas the emission intensity of the sample, containing Pb of 0.5 wt% or less, increase with temperature.
Therefore, the blue CL emissions found in barite might be composed of an impurity center of Pb-ion activator or sensitizer, and the 3.28 eV component may be composed of SO42-defect centers.
[1] Marshall, J. (1988) Cathodoluminescence of geological materials, Unwin Hyman, 1-146.
[2] Hirotsugu, N. et al. (2004) Temperature effect on cathodoluminescence of anhydrite.