The reinterpretation of the zero-field double resonance spectra of the lowest excited 3T 1u state of the F center in CaO in terms of random internal strain of E g symmetry

Abstract

The zero-field double resonance spectra of the relaxed excited 3T 1u state of the F center in CaO were determined and interpreted previously. In the present paper the phosphorescence microwave double resonance (PDMR) spectra are reinterpreted in terms of random internal strain of E g symmetry. The strain variables of the subensemble of F centers responding to a particular microwave-induced transition are exclusively determined by the microwave and the phosphorescence frequency. Consequently, the level structure in this subensemble can be calculated. To each PMDR spectrum, two graphical representations describing the possible spread in the phosphorescence frequency and the vibronic level structures of the F centers contributing to the PMDR signal are related. From these graphical representations, the occurring radiationless transitions can be traced. It is shown that, at the low energy side, the bounds of the PMDR lines are determined by the random strain distribution whereas the upper bounds are determined by fast radiationless transitions or by the lack of a population difference between the spin levels involved in the microwave-induced transition.