[S-MP47_1PO1] Physics and Chemistry of Minerals

[SMP47-P16] Cathodoluminescence characterization of terrestrial and extraterrestrial alkali-halide minerals

*Eisuke YOSHIDA¹, Hirotsugu NISHIDO¹, Kiyotaka NINAGAWA¹ (1.Okayama University of Science)

Luminescence of natural alkali halides such as halite and sylvite is characterized by structural defects related to F-center (+p) and V-center (+e). On their CL (cathdoluminescence), however, scarcely has been reported so far. Since asteroidal water was discovered as fluid inclusion in halite from H5 chondrite, Monahans (1998), alkali halides in meteorites have been extensively investigated for understandings of aqueous alteration and thermal metamorphism on the parent body. Therefore, luminescence features of halides can provide valuable information on such issues. In this study we have measured CL spectra of terrestrial and extraterrestrial halite samples to clarify luminescence centers in various types of halite. Halite crystals of terrestrial origin and small halite particles in ureilite meteorites were selected for CL measurements. All samples were prepared using oil while cutting and polishing without water. Also cleavage fragments of terrestrial samples were used for CL spectral measurements after carbon coating.All samples exhibit weak blue to greenish blue CL with broad band emissions from 350 to 650 nm. CL spectra corrected for total instrumental response were converted into energy units for spectral deconvolution using a Gaussian curve fitting, because Gaussian curve in energy units can be assigned to one specific type of emission center (Stevens-Kalceff, 2009). The deconvoluted components can be assigned to the emission centers related to V_k (+e), F (+p), V_F (+e), Mn²⁺ (Na⁺) and Mn²⁺ (interstitial) by referring to Gorobets and Rogojine (2002). The CL spectra of terrestrial halite at room temperature are consisted of five components at 3.34 eV, 3.05 eV, 2.46 eV, and 2.28 eV and at 2.00 eV. At low temperature the emission of Mn2+ impurity center is enhanced due to an increase in the probability of radiation transition. In the case of high-energy emission, a decrease in sample temperature reduces the intensity of F-center emission, but sensitizes the intensity of V_k-center emission, suggesting the energy transfer from F-center to V_k-center. The CL spectral analysis of terrestrial sylvite at room temperature confirms four emission components at 3.32 eV, 2.97 eV, 2.53 eV and 1.89 eV.Halite in the meteorite of polymict ureilite (Dar al Gani 319) gives a broad emission band in blue region, which is deconvoluted into two components at 2.70 eV for unknown center and at 3.11 eV for F-center. However, no emission in red region associated with Mn impurity center has not recognized in ureilite halite. It implies that high-energy radiation in cosmic space might break up the crystal fields around Mn ions.