Thermally Detected Electron Spin Resonance of Fe2+ in LiNbO3
Fe2+ is an important sensitizer of the photorefractive effect of LiNbO3. Thermally detected electron spin resonance at 35 GHz was used to detect this non-Kramers ion and to analyze the properties of its lowest states. ESR is found to be caused by electrically induced ΔmS = ±2 transitions between |mS = ±1> levels lying ∿15 cm-1 above the|ms = 0> groundstate. This splitting is caused by second order spin orbit coupling within the singlet orbital groundstate. The next orbital levels, a doublet, split-off by the trigonal crystal field, lies at ≥ 600 cm-1 above the groundstate. Strong low symmetry perturbations lead to very wide and asymmetric lines.