We show that the structure of transparent oxy-fluoride glass-ceramics formed by heat treatment of glasses of typical composition 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2):3.5(ErF3) mol% consists of ~12 nm diameter,Er3+-doped, â -PbF2 nano-crystals embedded in a silica-based glass network and connected to it via non-bridging O and F anions, or fluorine linkages such as Pb-F-Cd and Pb-F-Zn. It is proposed that the glass network structure is mostly chain-like and dominated by Si(O ,F)4 tetrahedra with two bridging O and two non-bridging O and/or F atoms (Q2 units).SiO4 tetrahedra with zero and one bridging O(Q0 and Q1 units, respectively)are also present in the glass structure, in the approximate proportion Q0:Q1:Q2 =1 :1 :3, a characteristic which appears to be of primary importance.The flexible,chain-like glass-network, with many broken bonds, results in easy accommodation of the Er3+-doped PbF 2 nano-crystals, which are grown by heat-treatment of the precursor glass.The boson peak in the Raman spectrum of the precursor glass decreases in intensity upon ceramming and is partly converted to narrowcrystalline peaks at lower frequency, consistent with the precipitation of PbF2 crystalline nano-particles. It is suggested that the boson peak involves localized vibrations of broken or stretched Pb-F bonds. The mean free path for these vibrations increases with ceramming, which involves partial crystallization of the glass network, resulting in a shift of the boson peak vibrations to lower-frequency crystalline peaks.
The structure of Er3+-doped oxy-fluoride transparent glass-ceramics studied by Raman scattering
Ferrari M;
2003
Abstract
We show that the structure of transparent oxy-fluoride glass-ceramics formed by heat treatment of glasses of typical composition 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2):3.5(ErF3) mol% consists of ~12 nm diameter,Er3+-doped, â -PbF2 nano-crystals embedded in a silica-based glass network and connected to it via non-bridging O and F anions, or fluorine linkages such as Pb-F-Cd and Pb-F-Zn. It is proposed that the glass network structure is mostly chain-like and dominated by Si(O ,F)4 tetrahedra with two bridging O and two non-bridging O and/or F atoms (Q2 units).SiO4 tetrahedra with zero and one bridging O(Q0 and Q1 units, respectively)are also present in the glass structure, in the approximate proportion Q0:Q1:Q2 =1 :1 :3, a characteristic which appears to be of primary importance.The flexible,chain-like glass-network, with many broken bonds, results in easy accommodation of the Er3+-doped PbF 2 nano-crystals, which are grown by heat-treatment of the precursor glass.The boson peak in the Raman spectrum of the precursor glass decreases in intensity upon ceramming and is partly converted to narrowcrystalline peaks at lower frequency, consistent with the precipitation of PbF2 crystalline nano-particles. It is suggested that the boson peak involves localized vibrations of broken or stretched Pb-F bonds. The mean free path for these vibrations increases with ceramming, which involves partial crystallization of the glass network, resulting in a shift of the boson peak vibrations to lower-frequency crystalline peaks.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
