ODMR of Triplet States of Self-Trapped Excitons in Li_2GeO_3 Crystals

摘要

In the X-ray-induced broad luminescence band of the self trapped excitons (STE) at 2.7eV an optically detected paramagnetic resonance (ODMR) spectrum was measured at 24GHz (K-band) and 1.5 K. The sets of the ODMR lines can be understood as originating from triplet spin systems (S=1) with orthorhombic fine structure (FS) tensors (Enot=0). We obtained two different triplet states with somewhat different FS interaction parameters, but very similar orientations of the principal axes (within 5 degrees). The principal axis z of each of the FS tensors makes an angle of about 25 degrees with the a- axis in the c-a plane. This direction is close to the Ge-O nonbridging bond direction. The nearly isotropic g value g=2.2 may be explained as being due to an unpaired spin of the electron component of the triplet state localized on Ge as Ge~(3+) (4s~1).