The non-direct band gap in borate glasses; a brief discussion on analysis methodologies and its interpretation

There is great interest in the study of the optical properties of materials such as glasses, due to their possible technological applications and from a fundamental point of view. For this reason, an attempt has been made to advance the understanding of the existence of optical band gap in this type of material. In recent times, several ways of analyzing the dependence of the absorption coefficient with energy have been proposed. Using lead, strontium, and barium borate glasses as a model, this dependence has been analyzed. For this, we considered the glass structure and the corresponding crystal structure, and the value of the optical band gap energy has been discussed considering the theory of Mott and Davis and comparing with values of crystals and glasses of similar composition. Here, we used a correction method, that takes into account intrinsic defects, to obtain the values of optical band gap energies in the framework of a non-direct transition. We also include DFT simulations of the corresponding crystalline compounds and the band gap was evaluated. The absorption coefficient obtained from simulations shows the same trend that the experimental one.