A criterion is introduced to achieve the assignment of the optical features observed in the excitation spectra of Bi3+ ions incorporated in closed-shell transition metal oxides. The model is based on the calculation of the energy associated with the lowest 1S0 → 3P1 intra-ionic transition of Bi3+ (A-like transition), the metal-to-metal charge transfer (D-like transition) and the Stokes shift of the corresponding emission.