Low symmetry Co2+ centers in strontium oxide crystals

EPR and optical spectra have been investigated for SrO cobalt-activated cubic crystals. The EPR spectra (T=4.2 deg K) indicate that there are two types of centers of Co2+(3d7) with S'=1/2 and ν=7/2. The ν centers possess the Csub(2v) symmetry and are characterized by the following g factors: gsub(z)=2.134, gsub(x)4.171 and gsub(y)04.994. The second type is characterized by the Csub(s) symmetry and the following g factors: gsub(z)=7.331, gsub(x)=2.386 and gsub(y)=1.694. In the optical spectrum bands of Co2+ are observed at T=21 deg K and T=300 deg K. The bands correspond to the 4T1(F)→4A2 and →4T1(P) transitions, the 4T (P) band being split into three components (the total splitting amounts to 1.200 cm-1). The oscillator strength of both bands temperature independent. The parameters of the cubic part of the crystal field have been determined: Dsub(q)=380 cm-1 and B=760 cm-1. Thus both EPR and optical spectra point to the presence of Co2+ low-symmetry centers in SrO crystals and to the absence of cubic centers. Models for these two types of centers are discussed; they are Models for these two types of centers are discussed; they are based on the assumption of the noncentral position of a Co2+ ion in the SrO crystal lattice