Configurational coordinate diagram Stokes shift

The parameter S measures the interaction between the dopant ion and the vibrating lattice. Equation [5] shows that if S is large, the Stokes shift is also large. Equation [4] shows that S is immediately related to the offset of the parabolas in the configurational coordinate diagram (Fig. 3). This offset, AQ = Q o - Qo), may vary considerably as a function of the dopant ion and as a function of the vibrating lattice, as we will see below. 

Let us consider the configurational coordinate diagrams of Fig. 5 in order to understand the relevant physical processes. Figure 5a presents essentially the same information as Fig. 3. Absorption and emission transitions are quite possible and are Stokes-shifted relative to each other. The relaxed-excited state may, however, reach the crossing of the... 

Three contributions to the Stokes shift of ion emission have to be taken into account [23], This must be done in a multidimensional configurational coordinate diagram and is mentioned here as an illustration of the complicated nature of this emission and, especially, of the relaxation into the excited state. We will restrict ourselves to octahedral coordination. 

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