Dual role of the six-coordinated molybdenum and lead ions in novel of photochromic properties of the molybdenum–lead–borate glasses

Transparent glasses were prepared by conventional melting–quenching method in the xMoO3·(100 − x)[3B2O3·PbO] system where 0 ≤ x ≤ 15 mol%. By increasing the MoO3 content up to 20 mol% the PbMoO4 crystalline phase appears. These systems exhibit a photochromic effect which can be induced through laser exposures (λ = 633 nm) directly on the bulk sample. Structural investigations by FTIR spectroscopy show that the photosensitive effect is due to a reduction of Mo6+ to Mo4+ and/or Mo5+ promoted by the oxidation of Pb2+ and some structural changes of the borate network.