Study on the contribution of the charge transfer excited states in Ba2MgGe2O7 : Cr4+ crystal to g factor

A complete high-order perturbation formula of g factor for cubic 3d2 MX4 clusters was established. In the formula, not only the contributions of the crystal-field (CF) mechanism (which is related to the CF excitations) to the g-shift Δg(=g-gs), but also the contributions of the charge-transfer (CT) mechanism (related to CT excitations) were considered. Using the formula, the g factor of Ba2MgGe2O7 : Cr4+ was calculated. The result was in agreement with the observed value. It was found that the calculated ΔgCT due to the charge-transfer mechanism is opposite in sign and about 38% in magnitude, compared with the calculated ΔgCF due to the crystal-field mechanism. So, for a high valence 3dn ion in crystals, the reasonable explanation of g factor should take into account the contributions of both crystal-field and charge-transfer mechanisms.