Recent spectral studies by Sanz et al. [27] and ElBatal [13] and ElBatal et al.
[28] have confirmed that the UV-near visible absorption bands in the range 200–500 nm observed in bismuth borate
and bismuth silicate glasses are correlated with absorption of both Bi3+ ions present in high content and also to absorption of Fe3+ ions present as unavoidable trace iron impurities within the chemicals used for the preparation of the base undoped bismuth silicate glass.