Optical absorption and electron paramagnetic resonance of Cu2+ ions in a low dimensional CaCu(HCOO)4 single crystal

Optical absorption and electron paramagnetic response (EPR) of Cu2+ ions in a CaCu(HCOO)4 single crystal have been studied. Analysis of EPR spectra using crystal field theory indicates that Cu2+ ions are in tetragonally distorted (elongated) octahedral sites. The optical absorption in the UV-visible region are characterized by a charge transfer band and cubic field splitting of the 3d energy level of the Cu2+ ion, but in the near-IR the absorptions at 4225, 4310, 5000, 5714 and 6622 cm−1 are attributed to the transitions between the admixed quantized energy levels of copper and oxygen orbitals.