Neodymium and Erbium Coordination Environments in Phosphate Glasses

The local structures of Nd3+ and Er3+ ions in two series of rare-earth (RE) phosphate glasses with nominal compositions xR203-(1-x)P2O5, where R=Nd and Er and 0.05≤x≤0.28, have been characterized by LIII-edge extended x-ray-absorption fine-structure spectroscopy (EXAFS). The RE coordination number depends on the R2O3 content, decreasing from 9.0 (10) oxygen nearest neighbors in ultraphosphate compositions (x\u3c0.15) to 6.4 (9) oxygen nearest neighbors for the metaphosphate (x∼0.25) compositions. The average Er-O bond distance decreases from 2.29 (1) to 2.23 (1) Å, and the average Nd-O bond distance decreases from 2.40 (1) to 2.37 (1) Å over the same compositional range. The changes in coordination environments are consistent with the conversion of isolated RE polyhedra to clustered RE polyhedra sharing common oxygens as the number of available terminal oxygens per RE ion decreases with increasing x

Preparation, properties and structure of rare-earth phosphate glasses

Three series of glasses of the formula xRE2O3·(1-x)P2O5, where 0 ≤ x ≤ 0.3 and RE = Nd, Gd, or Er, were prepared. Each glass series exhibits very similar property trends. Glass transition temperature (Tg) goes through a minimum at approximately 7 mol% RE2O3. Compositionally dependent increases are observed for both density and refractive index with RE2O3 additions. The densities increase from 2.4 g/cm3 for vitreous P2O5 to around 3.5 g/cm3 for the x = 0.30 compositions, and the refractive indices increase from 1.5 to around 1.6 over the same compositional range. The ionic packing fractions decrease with increasing RE2O3 from 0.42 to 0.33. The infrared (IR) spectra indicate a systematic decrease in phosphate connectivity as the RE2O3 concentrations are increased and the RE3+ ions modify the network. Extended x-ray absorption fine structure spectroscopy (EXAFS) studies show RE coordination environments very similar to those of the corresponding ultra- and meta-phosphate crystals. Coordination numbers decrease from about eight to six with increasing RE2O3 contents in the range from 15 to 25 mol% RE2O3. A less dramatic decrease occurs for the RE-O bond lengths over the same compositional range. In the Nd series, fluorescence lifetimes decrease dramatically with increasing Nd2O3. Residual water also appears to have an effect on fluorescence lifetimes --Abstract, page iii

Glasses and Glass-ceramics in the SrO-TiO₂-Al₂O₃-SiO₂-B₂O₃ System and the Effect of P₂O₅ Additions

The glass formation abilities of various compositions in SrO-TiO2-Al2O3-SiO2, SrO-TiO2-B2O3-SiO2, SrO-TiO2-Al2O3-B2O3, and SrO-TiO2-Al2O3-SiO2-B2O3 systems were studied.Many new compositions were found to be suitable for the casting of crack-free, optically clear glasses of different color and with glass transition temperatures ranging from 595 to 775 C. The crystallization behavior, structure, and thermal expansion behavior of selected glasses were analyzed by DTA, XRD, dilatometry, and heat treatment. The effect of P2O5 on the glass structure and crystallization behavior was also studied. P2O5 played a dual role depending on composition. In some glasses it acted as a nucleating agent while in others it suppressed crystallization. Heat treatment of borate and borosilicate glasses transformed them into glass-ceramics while comparable SrO-TiO2- Al2O3-SiO2 glasses showed a lower tendency to crystallize and form glass-ceramics under the same conditions

An EXAFS Investigation of Rare-Earth Local Environment in Ultraphosphate Glasses

The local structures around rare-earth ions in rare-earth ultraphosphate glasses (nominally 15RE2O3-85P2O5, mol%, RE = Nd, Sm, Gd, Ho, and Er) and metaphosphate glasses (nominally 25RE2O3-75P2O5, mol%, RE = Nd, Gd, and Er) have been studied by extended X-ray absorption fine structure spectroscopy (EXAFS) at the respective rare-earth LIII edges. The RE-O distance decreases with increasing atomic number of the rare-earth ion for both ultra and metaphosphate glasses. On average, RE-O distances for metaphosphate glasses are shorter than those for ultraphosphate glasses of comparable compositions. There are 7-8 oxygen nearest neighbors in the first co-ordination sphere around rare-earth ions in ultraphosphate glasses and not, vert, similar6 oxygens in the first co-ordination sphere around rare-earth ions in metaphosphate glasses. There is no systematic dependence of the RE-O co-ordination number on the atomic number of the rare-earth ions in either compositional series. The second co-ordination shell around rare-earth ions in ultraphosphate glasses consists of phosphorus ions for all but the samarium ultraphosphate glass, with a RE-P distance between 3.53 and 3.85 Å and co-ordination numbers between 3 and 5. No RE-RE correlations were found within a distance of 4.5 Å

An EXAFS Investigation of Rare-Earth Local Environment in Ultraphosphate Glasses

The local structures around rare-earth ions in rare-earth ultraphosphate glasses (nominally 15RE2O3-85P2O5, mol%, RE = Nd, Sm, Gd, Ho, and Er) and metaphosphate glasses (nominally 25RE2O3-75P2O5, mol%, RE = Nd, Gd, and Er) have been studied by extended X-ray absorption fine structure spectroscopy (EXAFS) at the respective rare-earth LIII edges. The RE-O distance decreases with increasing atomic number of the rare-earth ion for both ultra and metaphosphate glasses. On average, RE-O distances for metaphosphate glasses are shorter than those for ultraphosphate glasses of comparable compositions. There are 7-8 oxygen nearest neighbors in the first co-ordination sphere around rare-earth ions in ultraphosphate glasses and not, vert, similar6 oxygens in the first co-ordination sphere around rare-earth ions in metaphosphate glasses. There is no systematic dependence of the RE-O co-ordination number on the atomic number of the rare-earth ions in either compositional series. The second co-ordination shell around rare-earth ions in ultraphosphate glasses consists of phosphorus ions for all but the samarium ultraphosphate glass, with a RE-P distance between 3.53 and 3.85 Å and co-ordination numbers between 3 and 5. No RE-RE correlations were found within a distance of 4.5 Å