Borates, Stokes shift

Table III shows for a series of borates how the Stokes shift (i.e., AQ) increases if the size of the host lattice cation increases (100). In ScBOa the rare-earth ions are strongly compressed and the surroundings are stiff. Small Stokes shifts result for Ce, Pr, and Bi, but not for the smaller Sb . Note, however, that the Stokes shift of the 4/ -5d transitions is less sensitive to the surroundings than that of the 5s-5p transitions. If the data of Table III are extrapolated to, for example, borate glasses, it can be concluded that we find no efficient Sb or Bi emission, but for or Pr this may still be the case. This is what has been observed experimentally.

Inspecting Figs. 14.3, 14.4 14.5 and Table 14.1 shows that, as stated earlier for Bi -doped alkali or alkali-earth borate binary glasses, the excitation peak regularly shifts red and the emission peak shifts blue with increasing concentration of alkali or alkali-earth elements. As a result, the Stokes shift decreases. How does all this happen To elucidate it, information on glass microstructural changes is helpful. 

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