Magnetic dipole origins of the ³A _2g→ ³T _2g transition in Ni(ii) doped MgO

Magnetic circular dichroism and magnetic linear dichroism spectroscopy have been used to study the near infrared 3A2g→3T2g transition of Ni(ii) doped MgO. Two sharp electronic origins are observed and it is show that their polarisation behaviour follows that expected from calculations in detail for magnetic dipole allowed transitions in octahedral symmetry. Not all transitions to the spin-orbit components of the 3T2g state are observed. We put forward an explanation for why some components are missing, even though they are expected to be of comparable intensity, in terms of the different coupling to the JahnTeller active tetragonal distortion in the excited state. The two lower energy spin-orbit split components are nearly independent of this distortion, while the two higher energy components are strongly dependent. We also examine the double quantum transition in the electron paramagnetic resonance spectrum and estimate the magnitude of the random strain of tetragonal symmetry in the MgO lattice.