where h is nephelauxetic functions of the ligand, Bfree is the value of
the free (gaseous) Cr3+ ion, and k is the central metal ion. The latter
in case of Cr3+ is kCr3þ ¼ 0:21 [8,15]. The obtained value of the interelectronic
repulsion Racah parameter B is lower than the value of
Bfree ¼ 918 cm1; as given in Table 1. The estimated value of h
parameter decreases as you go from KCl to KBr to KI, mirroring a decrease
in the covalent bonding nature between Cr3+ and the surrounding
ligands, as well as an increased d-electrons localization
[15]. Moreover, the spectra of investigated glasses exhibit some
dips, for such characteristic dips are seen in this samples, a fine
structure corresponding to a dips at about 630 and 677 nm as
show in the insert figure, which is attributed to the Fano anti-resonances
resulting from the interaction of the 2T1g and 2E2g with the
vibrationally broadened 4T2g state [8,11,15].