xLa2O3-(100 − x)Ga2O3 binary glasses were synthesized by an aerodynamic levitation technique. The glass-forming region was found to be 20 ≤ x ≤ 57. The refractive indices were greater than 1.92 and increased linearly with increasing x. The polarizabilities of oxide ions were estimated to be 2.16–2.41 A3, indicating that the glasses were highly ionic. The glasses were transparent over a very wide range from the ultraviolet to the mid-infrared region. The widest transparent window among the oxide glasses was from 270 nm to 10 μm at x = 55. From the Raman scattering spectra, a decrease in bridging oxide ions and an increase in non-bridging oxide ions were confirmed to occur with increasing La2O3 content. The maximum phonon energy was found to be approximately 650 cm−1, being one of the lowest among oxide glasses. These results show that La2O3-Ga2O3 binary glasses should be promising host materials for optical applications such as lenses, windows, and filters over a very wide wavelength range.

Low phonon energies and wideband optical windows of La 2 O 3 -Ga 2 O 3 glasses prepared using an aerodynamic levitation technique

A high-refractive-index glass with the composition of 0.30La2O3–0.70Nb2O5 was prepared in bulk form by containerless processing without using network former oxides. The glass transition temperature was 725 °C and the first crystallization peak temperature was 805 °C. The glass was colorless and transparent from 345 nm to 7.3 µm. The refractive index was higher than 2.3 in the visible range, and the Abbe number estimated from the Drude–Voigt relationship was 20.4. These results indicate that the niobate glass system would be useful for optical applications in the visible to infrared region.

https://iopscience.iop.org/article/10.1143/APEX.3.102601/pdf

High Refractive Index of 0.30La2O3–0.70Nb2O5 Glass Prepared by Containerless Processing

Presently described are retroreflective articles, such as pavement markings, that comprise transparent microspheres partially embedded in a (e.g. polymeric) binder. Also described are (e.g. glass-ceramic) microspheres, methods of making microspheres, as well as compositions of glass materials and compositions of glass-ceramic materials. The microspheres generally comprise lanthanide series oxide(s), titanium oxide (TiO2), and optionally zirconium oxide (ZrO2).

Pavement marking, reflective elements, and methods of making microspheres

Effect of substituting Al2O3 and ZrO2 on thermal and optical properties of high refractive index La2O3–TiO2 glass system prepared by containerless processing

(100−x)La2O3-xNb2O5 glasses with high refractive indices (>2.1) and low wavelength dispersion were prepared by containerless processing. All the glasses were colorless and transparent in the visible region. The glass forming region was divided into two regions: a high-La2O3-content (39 ≤ x ≤ 42) region and a high-Nb2O5-content (60 ≤ x ≤ 75) region. The dependence of the physical properties on the composition for these two types of glasses was different, implying that the high-La2O3-content glasses (La glasses) and high-Nb2O5-content glasses (Nb glasses) were intrinsically different. A large difference in the molar volumes of the two types of glasses indicated that the Nb glasses were more densely packed than the La glasses. Furthermore, the oxygen polarizabilities estimated from the molar volumes and refractive indices were greater than 2.43 A3 for the La glasses, while those for the Nb glasses decreased from 2.43 A3 with decreasing x. The large oxygen polarizabilities, as compared to those of conventional optical glasses, indicate a particularly high degree of ionic character for the component elements in the glasses. These results suggest that both the La and Nb glasses are desirable materials for high-valued optics, such as lenses with high power and high resolution as well as wide viewing angles used for a digital camera in a smartphone.

Thermal and optical properties of La_2O_3-Nb_2O_5 high refractive index glasses

Thermal image furnace melting and twin-roller quenching were used to prepare glasses containing large amounts of rare earth oxides in Ln2O3-MXOY systems (Ln2O3=La2O3, Nd2O3, Y2O3; MXOY=SiO2, Al2O3, TiO2, Nb2O5).The glass-forming regions were found at the following compositions close to the eutectic points of the phase diagrams: (20-30)Ln2O3-(70-80)SiO2, 60Ln2O3-40SiO2, 20Ln2O3-80Al2O3, 20Ln2O3-80 TiO2, (20-30)Ln2O3-(70-80)Nb2O5 and 60Ln2O3-40Nb2O5. The glass transition temperature Tg was determined by DTA. All the glasses showed high glass transition temperatures over 700°C. Although Tg increased or decreased with Ln2O3 content depending upon the system, the change was linear with Ln2O3 content around the eutectic compositions. This seems to indicate that there is no peculiar behavior of viscosity itself at the eutectic compositions. The liquidus viscosity becomes the maximum at the eutectic compositions due to low liquidus temperatures, which makes glass-formation easier at the eutectic compositions.A glass model consisting of four-coordinated aluminum units was proposed for Ln2O3-Al2O3 glasses based on the results of IR spectra and observed AlKα chemical shifts. On the other hand IR spectra of Ln2O3-TiO2 glasses showed a mixture of six- and four-coordinated titanium units.Visible and ultraviolet absoption spectra of Nd3+ were studied on Nd2O3-MXOY glasses. The peak positions of these absorption bands moved towards lower wave numbers linearly with increasing compositional basicity of the glasses. Their color changed from purple-like blue to green-like blue, as the absorption bands shifted towards lower wave numbers.

Hiromitsu Kozuka

Papers

Preparation and properties of binary oxide glasses containing rare earth oxides.