Second-harmonic generation and structural rearrangements in multicomponent antimonite glasses by electrothermal poling

Electrothermal poling is shown here to effectively induce second-order nonlinear effects in heavy-metal oxide antimonite glasses. In M₂O–PbO–WO₃–Sb₂O₃ (M = Li, Na, K) glasses, the poling-induced second-harmonic generation intensity is five times larger than in silica (Infrasil) for M = Na, twice as large as in silica for M = Li, and smaller than in silica for M = K. X-ray photoelectron spectroscopy suggests that antimony ions exist predominantly in the trivalent oxidation state in the studied glass samples. Raman and infrared spectroscopy confirm that the glass network is comprised of SbO₃, WO₄, WO₆, and PbO₄ units—with some SiO₄ moieties due to leaching from the silica crucible. The WO₄ units appear to exist in two distinct sites, as evidenced by comparison of the vibrational spectra of alkali–tungsten–antimonite glasses with those of previously reported crystalline tungstate phases. The alkali type influences the equilibrium between tetrahedral tungstate anions, [WO₄]²⁻, and the isomeric partially polymerized octahedral tungstate units, [WØ₄O₂]²⁻ (Ø denotes a bridging oxygen). Raman spectroscopy line scans were used to track near-surface structural changes on the anode side of poled glasses. They reveal that the tungstate equilibrium is also affected by poling. At the anode side, the population of partially polymerized [WØ₄O₂]²⁻ species increases at the expense of anionic [WO₄]²⁻ species. This yields a net increase in the average bond length of the network forming constituents, which is commensurate with poling-induced structural changes observed in other systems experimentally and computationally.