Enstatite in Yamato 86004 classified as EH melt rock shows cathodoluminescence (CL) zonation as arranged in a concentric pattern from within outward blue, light blue, red and non-CL areas (fusion crust). The zonation observed in the meteorite results from different distribution ratio of the enstatite with various CL colors. CL spectra of the enstatite have two broad emission bands at around 400 nm in the blue region and at around 670 nm in a red region. The emission components obtained by a spectral deconvolution can be assigned to three defect centers (2.73, 3.13–3.15 and 3.77 eV) in a blue region and to impurity centers of Cr3+ ion (1.71 eV) and Mn2+ ion (1.86–1.91 eV) in a red region. According to the CL related to structural defects in the enstatite, blue-CL enstatite might be originally formed from the melt by a quenching from the melt on the surface of parent body. The enstatite with light blue and red CL might be thermally altered from blue-CL enstatite with phase transitions during a flash heating when the meteorite passed through the atmosphere. Therefore, the color CL zonation reflects a thermal history recorded in the meteorite.
Hirotsugu Nishido, Taro Endo, Kiyotaka Ninagawa, Masahiro Kayama and Arnold Gucsik
Cathodoluminescence (CL) spectral analysis has been conducted for luminescent forsterite (olivine) of terrestrial and meteoritic origins. Two emission bands at 3.15 and 2.99 eV in blue region can be assigned to structural defect centres and two emission bands at 1.91 and 1.74 eV in red region to impurity centres of Mn2+ and Cr3+, respectively. These emissions reduce their intensities at higher temperature, suggesting a temperature quenching phenomenon. The activation energy in the quenching process was estimated by a least-square fitting of the Arrhenius plots using integrated intensity of each component as follows; blue emissions at 3.15 eV: 0.08–0.10 eV and at 2.99 eV: 0.09–0.11 eV, red emissions at 1.91 eV: ∼0.01 eV and at 1.74 eV: ∼0.02 eV. The quenching process can be construed by the non-radiative transition by assuming the Mott-Seitz model. The values of activation energies for blue emissions caused by structural defects correspond to the vibration energy of Si-O stretching mode in the lattice, and the values for red emissions caused by Mn and Cr impurity centres to Mg-O vibration energy. It implies that the temperature quenching energy might be transferred as a phonon to the specific lattice vibration.
Masahiro Kayama, Hirotsugu Nishido, Shin Toyoda, Kosei Komuro, Adrian Finch, Martin Lee and Kiyotaka Ninagawa
Cathodoluminescence (CL) of minerals such as quartz and zircon has been extensively studied to be used as an indicator for geodosimetry and geochronometry. There are, however, very few investigations on CL of other rock-forming minerals such as feldspars, regardless of their great scientific interest. This study has sought to clarify the effect of He+ ion implantation and electron irradiation on luminescent emissions by acquiring CL spectra from various types of feldspars including anorthoclase, amazonite and adularia. CL intensities of UV and blue emissions, assigned to Pb2+ and Ti4+ impurity centers respectively, decrease with an increase in radiation dose of He+ ion implantation and electron irradiation time. This may be due to decrease in the luminescence efficiencies by a change of the activation energy or a conversion of the emission center to a non-luminescent center due to an alteration of the energy state. Also, CL spectroscopy of the alkali feldspar revealed an in-crease in the blue and yellow emission intensity assigned to Al-O−-Al/Ti defect and radiation-induced defect centers with the radiation dose and the electron irradiation time. Taken together these results indicate that CL signal should be used for estimation of the α and β radiation doses from natural radionuclides that alkali feldspars have experienced.