“…Structural relaxation of glasses may involve local rearrangements of atoms or, under certain conditions, may lead to a partial or complete crystallization of the glass. Glasses with a high content of heavy metals, like Bi 2 O 3 and PbO, are intensely investigated because of their properties such as high density, high refractive index, excellent IR transmission and high polarisability [1][2][3][4][5]. All of these properties are exploited in applications such as thermal and mechanical sensors [5], wave-guides in non-linear optics [6], scintillation detectors in high-energy physics [6,7].…”