Defects in CaF₂ caused by long-time irradiation and their response to annealing

Abstract

Samples of CaF₂ irradiated for millions of years in nature were studied by several methods, including X-Ray diffraction, positron annihilation spectroscopy (PAS), photoluminescence spectroscopy (PLS) and transmission electron microscopy (TEM). It was found that the unexpectedly high density of radiation-induced defects present in the fluorite structure (documented by TEM) causes significant micro-strains. Even annealing up to 450°C cannot completely remove these micro-strains, which are stabilised by impurities. PAS and subsequent theoretical calculations revealed the behaviour of the defects during heating. The PL spectra of irradiated fluorite were also interpreted.

Keywords:

• fluorite
• microstructure
• defect
• positron annihilation spectroscopy
• photoluminescence spectroscopy
• transmission electron microscopy
• X-ray diffraction

Acknowledgements

This work was funded by the The Ministry of Education of The Czech Republic (projects MSM0021620855 and MS0021620834). Authors would like to acknowledge the help of Dr. Viktor Goliáš and Dr. Marek Chvátal. One of the authors (JV) acknowledges the support through the Centre of Nanotechnology and Materials for Nanoelectronics, LC510 (funded by the MSMT CR). RS thanks for the support through the research plan AV0Z30130516 of the Institute of Geology AS CR.