Energy level diagrams for octahedral environments

Energy level diagrams for ions in tetrahedral environments can be constructed by the same procedures as those described in the preceding pages for the octahedral case. We shall briefly outline here the procedure for d2. 

We will now explain the method of constructing an energy level diagram by treating the particular case of a d2 ion in an octahedral environment. For this system the free-ion terms, in order of increasing energy, are... 

By inspection of the energy level diagrams it is possible to see directly what sort of spectrum the ion should have in the given environment. For example, it can be seen from Figure 9.3 that a d2 ion in an octahedral complex, say [V(H20)J3+, should have three spin-allowed transitions, from the 37, ground state to the upper states 37, 3T, and 3A2. Experimentally, two absorption bands have been found at —17,000 and —24,000 cm-1, and these may be assigned to the T — 37 and 3T - 3T transitions if A0 is taken as —21,500... 

A correlation diagram for a d ion (e.g. Vt+) in an octahedral environment is shown in Fig. 12-7.2. What this diagram does is to demonstrate how the energy levels of the free ion behave as a function of the strength (A0) of the ion s interaction with a set of octahedrally disposed ligands. 

Figure 2 A Tanabe-Sugano diagram for a 3d impurity ion such as Cr. The octahedral crystal field increases along the x-axis and the energy levels split and shift as indicated. For zero crystal field the free ion LS states are indicated on the left. A dashed line indicates the crystal field strength relevant to ruby. The energy levels indicated appear in the absorption spectrum shown on the right. Luminescence is only from the lowest lying excited state, E. For materials that provide weaker field environments the T2 state is lower and much broader bandwidth emission is obtained. Reproduced with permission of Oxford University Press from Henderson B and Imbusch GF (1989) Optical Spectroscopy of Inorganic Solids. Oxford Clarendon Press.

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