Clarification of terminological confusion concerning the crystal field quantities vs. the effective spin Hamiltonian and zero-field splitting quantities in the papers by Bayrakçeken et al. [Spectrochim. Acta Part A 66 (2007) 462 and 1291]

The physically distinct notions: crystal field (CF) [or equivalently ligand field (LF)] and effective spin Hamiltonian, which comprises zero-field splitting (ZFS) [or equivalently fine structure (FS)], are often confused each with other in literature. Confusion of the type X = Y consists in referral to the quantity Y by the name X of another well-defined quantity. Most prevailing is the CF = ZFS confusion, i.e. labeling the actual ZFS/FS quantities as purportedly the CF/LF ones. Unique cases of the inverse ZFS = CF confusion, identified in recent papers by Bayrakçeken et al. [Spectrochim. Acta A 66 (2007) 462 and 1291], is discussed here. To clarify this confusion, clear distinction between operators of various nature used in electron magnetic resonance (EMR), optical spectroscopy, and related studies is provided. Other deficiencies in the two papers in question, which overlap to a large extent, and misinterpretations therein are critically commented on.