THERMAL FORMATION OF F2+ CENTERS IN KCL CRYSTALS

Thermal formation of F2+ centers in KCl crystals has been investigated in temperature region between 210°K and 270°K. KCl crystals containing electron traps such as Tl+ ions were X-rayed at room temperature and was illuminated with F light at 120°K. Negative ion vacancies thus produced from F centers began to move about 220°K and combined with F centers to from F2+ centers. The activation energy for the F2+ -center formation was estimated to be 0.52±0.03 eV. An absorption band at 1.35μ at room temperature was confirmed to arise from F2+ centers and to shift to 1.40µ at liquid helium temperature. The frequency of the lattice vibration influencing the ground state of the F2+ center was 2.9×1012 cps, which was almost the same value with that of the M center. The F2+ -center formation is discussed by assuming the covalent force acting between an F center and a negative ion vacancy. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.