Effect of radiation induced defects on the optical transitions of 3-d impurities

Research was conducted to identify the emission band at about 13,000 cm-1 of Ni2+ ions to study the radiation effect on this emission band and, to present the models and radiation mechanism of Mn2+ and Co2+ doped KMgF3 crystals. The mechanism which causes the enhanced intensity for the optical transitions of Mn2+ and Co2+ ions in irradiated KMgF3 crystals was also investigated. By examining two optical emission bands due to Ni2+ ions in each of four different crystals, KMgF3, KZnF3, MgO, and MgF2, it has been possible to unambiguously determine the origins of 20,000 cm-1--21,000 cm-1 band as arising from 1T2 to 3A2/sub g/ transition and 13,000 cm-1--14,000 cm-1 band as coming from 1T2/sub g/ to 3T2/sub g/ transition. The interpretation relies on the comparison of the measured transition energies in this work with existing optical absorption, emission, and excitation data, on the observation of spin orbit splitting for the first excited states and on the analysis of polarization measurements in MgF2:Ni. The emission bands at 680 nm for KMgF3:Mn and 670 nm for MgF2:Mn are tentatively assigned to Mn2+--F center-interstitial complexes, whereas the emission bands at 720 nm for KMgF3:Mn and 700 nm for MgF2:mn are due to Mn2+--F center complexes. The 658 nm (15,000 cm-1), 830 nm (12,000 cm-1), and 875 nm (11,000 cm-1) emission bands observed in irradiated KMgF3:Co apparently are due to Co2+--F center complex. The 658 nm band, 830 nm band and 875 nm band are tentatively assigned to the 2T1/sub g/ to 4T1/sub g/, 4A2/sub g/ to 4T1/sub g/, and 2E/sub g/ to 4T1/sub g/ transitions of Co2+, respectively. By the optical bleaching experiments, the unusually high strengths of radiation defect perturbed Mn2+ and Co2+ transitions appear to be due to exchange interactions between F centers and 3d impurities