Characterisation of (halogen)_3~(-) molecular ions formed in alkali borate glasses containing alkali halide

摘要

When alkali halides, such as KI and KBr, are added to alkali borate glasses. (halogen)_3~(-) molecular ions are formed. However, the role of the alkali oxide in the creation of (halogen)_3~(-) has not been previously reported. We have measured the optical absorption of KI containing potassium borate glasses with different K_2O concentrations. The present results reveal that the efficiency of I_3~(-) formation decreases with increasing K_2O concentration and disappears by 25 mol percent K_2O. On the other hand Raman spectroscopy indicates that the borate glass structure is gradually converted into triborate groups from boroxol rings, with increasing K_2O, up to 25 mol percent. A molecular orbital calculation has also been carried out to examine the charge transfer between the iodide molecular ion and the boroxol ring. As a result we conclude that the I_3~(-) molecular ion is bound to the boroxol ring.