However, an estimation of the optical
basicity can be made by using the average electronegativity (vav )
through the empirical formula aswhere xi and vi are, respectively, the concentration percentage and
the electronegativity of an oxide compound. The electronegativity
of the pure elements brought by using the Allen scale [21], the calculated
average electronegativity and optical basicity as a function
of potassium halides type is present in Fig. 2 for all samples. It is
clear that the average electronegativity decreases from KCl to KBr
and to KI samples as shown in Fig. 2a, this mainly due to the fact
that electronegativity of chlorine is larger than that of bromine
and iodine elements. Contrary, the optical basicity shows the expected
opposite behavior as shown in Fig. 2b; it increases when
replacing the KCl by KBr or KI. From the previously published work,
it was found that with increasing the optical basicity the tetrahedral
coordination of transition metal ions becomes preferential in the
host glasses