Manganese absorption in CaF2:Mn; I

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Abstract
We report detailed optical absorption spectra for Mn2+ in CaF2. The spectra from unirradiated samples, reported here for the first time, enable the 495-nm luminescence emission to be clearly assigned to a transition from the first excited 4T1g (4G) level to the 6A1g (6S) ground state. On the basis of the absorption curves energy level assignments are made for all of the 4G, 4D, 4P, and 4F levels. Racah parameters are evaluated and the reduction of these from their free-ion values, due to covalency effects, is estimated. A value of Dq=420 cm−1 is calculated and an Orgel diagram for this system is constructed. Finally, oscillator strengths for each of the transitions are estimated from the absorption spectra. The optical absorption spectra from gamma irradiated samples show a complex array of overlapping bands, most of which can be shown to be related to the presence of Mn. The thermal annealing of the bands is associated with the production of thermoluminescence at an emission wavelength of 495 nm. Although no definite models can be offered for the defects involved in these processes, they are believed to be complexes of Mn and radiation-induced defects (e.g., Mn/F centers).