HIGH THERMAL STABILITY OF THE OFF-CENTER PARAMAGNETIC Fe3+ IONS IN CHLORINATED SrCl2:Fe2+ CRYSTALS

The thermal stability above 300 K of the hole-trapped Fe3+ centers, formed by X-ray irradiation at 80 K in chlorinated SrCl2:Fe2+ crystals, has been investigated by Electron Paramagnetic Resonance. In the temperature range of 300 - 520 K, the trigonal Fe3+ center completely transforms into the cubic Fe3+ center, which further decays up to 700 K. The formation and transformation of the trigonal Fe3+ center, containing off-center Fe3+ ions, is associated with the presence and thermally activated movement of the interstitial Cl- ions, present in excess in chlorinated SrCl2:Fe2+ crystals.