Increasing GeO2 Content Research Articles

Exploring the interplay of structure, optical, magnetic and radiation shielding properties in GeO2/Bismuth borate glasses

This article investigates the structural, chemical, optical, and magnetic properties of borate bismuth glasses doped with increasing GeO2 concentrations. X-ray diffraction (XRD), Raman spectroscopy, density measurements, thermal analysis, UV–Vis absorption, and VSM studied the impact of GeO2 on the glass network. The XRD results of the study confirmed that glass is amorphous. The bulk density increased while the molar volume decreased with increasing GeO2 concentration. Glass transition temperature (Tg) slightly decreases due to weaker Ge–O bonds and lower cross-linking density. Crystallization temperature (Tc) increased as GeO2 disrupts the network, hindering crystal nucleation and growth. Optical band gap narrows with increasing GeO2, with direct and indirect gaps decreasing. Urbach energy (EU) rises with GeO2, indicating increased disorder in the glass network. Refractive index (n) and extinction coefficient (k) both increased with GeO2, attributed to non-bridging oxygen formation. VSM measurements reveal an increase in saturation magnetization from 0.1 to 0.3 emu/g with increasing GeO2 content. Mass attenuation coefficient (MAC) and linear attenuation coefficient (LAC) investigations showed the efficiency of the glass system for radiation attenuation at varying energies. The unique properties of these borate bismuth glasses doped with GeO2 show promise for various technological advancements in optoelectronics and radiation shielding.

Deep Ultraviolet Transparent Electrode: Ta-Doped Rutile Sn1–xGexO2

Transparent conductive oxides (TCOs) are key materials for highly efficient optoelectronic devices such as light-emitting diodes (LEDs) and photovoltaic cells. While high-performance TCOs have been developed for use in the visible light spectrum, few materials are identified as TCOs feasible for deep ultraviolet (DUV) devices, especially at wavelengths shorter than 280 nm (UV-C region). Herein, we demonstrate that an alloy of rutile SnO2 and isostructural GeO2, rutile Sn1–xGexO2 (SGO), is a promising host semiconductor for a DUV-TCO. The optical band gap for (001)-oriented rutile SGO epitaxial thin films grown on Al2O3 (10–10) substrates increases monotonically from 3.79 eV (x = 0) to 4.09 eV (x = ∼0.7) with increasing GeO2 content. The rutile SGO thin films with a low Ge content (x ≤ 0.36) exhibit a low electrical resistivity of 2–3 × 10–4 Ω cm on doping with Ta5+ as a donor impurity. The increase in carrier electrons simultaneously enhances the DUV transparency of the films owing to the Burstein–Moss effect, resulting in an optical band gap of ∼4.2 eV for the film with x = ∼0.30. Notably, Ta-doped rutile SGO thin films can also be grown on AlN substrates, and their performance as DUV-TCOs is superior to that of conventional TCOs and competitive with state-of-the-art DUV-TCOs. These results indicate that Ta-doped rutile SGO thin films are promising candidates for transparent electrodes on III–V nitride semiconductor-based DUV-LEDs.

Effect of the GeO2 content on the radiation resistance of Er3+ -doped silica glasses and fibers

In this work, Er/Al/Ge co-doped silica glasses with different GeO2 content (0–3 mol%), as well as Ge/Al co-doped silica glasses, are prepared by combining the sol–gel and high-temperature sintering methods. Further, the effects of the GeO2 content on the absorptions and emissions properties, and lifetimes of the glasses before and after 1KGy γ-ray irradiation are compared. The Er/Al/Ge co-doped silica fibers are prepared from a preform produced via modified chemical vapor deposition (MCVD) combined with nano sol-doping. The effects of Ge co-doping on the optical loss and amplifier gain of the Er-doped silica fibers (EDFs) before and after irradiation are also investigated. The related mechanism and species of the γ-ray radiation-induced color centers are revealed via radiation-induced-absorption (RIA) and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopies. The results revealed that co-doping with GeO2 considerably improves the radiation resistance of the glass and exerts a slight effect on the spectral properties of the Er/Al/Ge co-doped silica glasses before irradiation. The RIA and CW-EPR spectra revealed that the aluminum–oxygen hole center (AlOHC) defects reduce with increasing GeO2 content because the intermediaries, the Ge-related oxygen-deficient centers (GeODC(I) and GeODC(II)), exhibit stronger abilities to trap the holes compared with the [AlO4/2]− group. This reduces the RIA level in the visible and near-infrared regions of the Er/Al/Ge co-doped silica glass. The irradiation experiment on the fiber further confirmed that the radiation resistance of EDFs can be considerably improved by Ge co-doping.

Large Brillouin gain in Germania-doped core optical fibers up to a 98 mol% doping level.

Germanosilicate glasses are substantial materials in fiber optic technology that have allowed the control of optical properties such as numerical aperture, photosensitivity, dispersion, nonlinearity, and transparency toward mid-infrared. Here, we investigate stimulated Brillouin scattering in single-mode germanosilicate core fibers with increasing GeO2 content from 3.6mol% up to 98mol%. Our results reveal a wide Brillouin frequency shift tunability over more than 3GHz with a strong decrease down to 7.7GHz at high GeO2 content owing to the low acoustic velocity, while the Brillouin linewidth significantly broadens up to 100MHz beyond 50mol% of GeO2 content. In addition, large Brillouin gain up to 6.5 times larger than in standard silica fibers is also reported by means of a pump-probe experiment.

Synthesis and structural characterization of a new SbPO4-GeO2 glass system

This work presents the production and characterization of a new prolific binary glass system based on SbPO4-GeO2. The dependence of GeO2 content on thermal, structural and optical properties were investigated by means of thermal analysis, Raman, UV–Vis-NIR, infrared, M-lines and EPR spectroscopy. Glass transition temperatures remain constant around 410 °C when GeO2 content is increased, indicating that GeO4 units are not responsible for increasing the connectivity of PO4 units. Thermal stability linearly increases as a function of GeO2 content, reaching a value around 400 °C for glass containing 90 mol% of GeO2. Raman spectroscopy was used to evaluate the glass structural changes when GeO2 is incorporated from 30 to 90 mol% indicating a gradual change from a phosphate to a germanate glass skeleton. The optical window extends from 350 nm at UV region, up to 2.7 μm in the middle-infrared region limited by the multiphonon cut-off due to the strong OH absorption. M-lines technique shows that increasing GeO2 content decreases the refractive index, mainly because the lower concentration of higher polarizable antimony atoms. EPR spectra of heat treated V2O5 doped glasses, at different temperatures above the glass transition temperature, shows the characteristic eight-line hyperfine splitting spectrum. The spin Hamiltonian parameters obtained from the simulated spectra indicates that the paramagnetic tetravalent vanadium ions in the glasses exist as vanadyl form VO2+, located in axially distorted octahedral sites. For glasses treated at higher temperatures a second VO2+ component appears in the EPR spectra and the analysis of the spin-Hamiltonian parameters suggests that these vanadyl ions are in more tetragonal distorted octahedral sites than those in the glass.

Sintering kinetics at constant rates of heating: effect of GeO2 addition on the initial sintering stage of 3 mol% Y2O3-doped zirconia powder

The sintering behavior of 3 mol% Y2O3-doped zirconia powders with and without a small amount of GeO2 was investigated to clarify the effect of GeO2 addition on the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The sintering rate was accelerated by GeO2 addition, and increased with increasing GeO2 content. The mechanism, apparent activation energy (nQ), and apparent frequency factor (β0n) of diffusion at the initial sintering stage were estimated using the sintering-rate equations that are applicable to the CRH data. The sintering mechanism changed from grain-boundary (GBD) to volume diffusions (VD) by GeO2 addition, and both nQ and β0n of diffusion increased with increasing GeO2 content. It is, therefore, concluded that the enhanced sintering mechanism by GeO2 addition is explained by the GBD→VD change and increases in both nQ and β0n of diffusion at the initial sintering stage.

Addition of GeO2to Reduce the Viscosity of Parent Glasses for Low-Expansion, Transparent Glass?Ceramics Containing High-Quartz Solid Solutions

Parent glasses for fabricating glass–ceramics with nanometer-sized crystals usually have high viscosities, resulting in high processing temperatures. In this study, GeO2 was added to a transparent, near-zero thermal-expansion Li2O–Al2O3–SiO2 glass–ceramic to reduce the viscosity of the parent glass. The effects of this compositional modification on the viscosity and crystal-nucleation rate of the parent glasses, and on the crystal size, thermal expansion, and optical transparency of the resulting glass–ceramics were investigated. It was found that addition of GeO2 was useful in reducing the glass viscosity. Owing to the reduced nucleating rate with the increase in the GeO2 content, the nucleating times required for reaching the smallest crystal size, the lowest coefficient of thermal expansion, and the highest transparency were all increased. With increasing GeO2 content, the lowest coefficient of thermal expansion that can be reached for glass–ceramics increased (0.14–2.9 × 10−6 K−1). The highest transparency of the GeO2-containing glass–ceramics is almost as good as that of the GeO2-free glass–ceramic and is almost independent of GeO2 content when the crystal size is smaller than about 65 nm.

Effects of GeO2 on the thermal stability and optical properties of Er3+-doped germanate-tellurite glasses

Germanate-tellurite glasses with the molar compositions of x GeO2-(70-x) TeO2-5K2O-5Na2O-10Nb2O5-10ZnO-0.2Er2O3 (x=0,10, 25, 50, 70) have been investigated for developing 1.5μm fiber and planar amplifiers. Effects of GeO2 on the thermal stability and optical properties of Er3+-doped germanate-tellurite glasses have been discussed. It is noted that the thermal stability of the glasses are improved and the maximum phonon energy are increased by increasing GeO2. Adding GeO2 increases the Judd-Ofelt parameters Ω2, Ω6 but decreases the stimulated emission cross sections σe. According to the McCumber theory, the maximum peak of σe is 9.92×10-21cm2 at 1.53μm in germanate-tellurite glasses. The maximum FWHM of Er3+4I13/2→4I15/2 emission spectrum is 52 nm. In addition, the intensity of upconversion luminescence of the Er3+-doped germanate-tellurite glasses decreases rapidly with increasing GeO2 content.

Properties of Tm3+‐Doped Germanotellurite Glasses for S‐Band Amplifier

Optical and material properties of (75−x)TeO2–xGeO2–20ZnO–5Na2O–0.1Tm2O3 glasses were investigated as candidate materials for an S‐band Tm‐doped fiber amplifier (TDFA). With increasing GeO2 content, the lifetime and the quantum efficiency of the 1.46 μm emission decreased slightly, while the emission bandwidth, the Vickers hardness, and thermal stability of the glass improved monotonically. Above 20 mol% GeO2, the quantum efficiency decreased more rapidly with increasing GeO2. We conclude that addition of a small amount of germania may improve material properties without deteriorating the optical properties of doped Tm3+, and thus the germanotellurite fiber may be a more reliable material for the S‐band TDFA in wavelength‐division‐multiplexing telecommunication.

Thermal analysis and optical transition of Yb3+, Er3+ co-doped lead–germanium–tellurite glasses

In this article, we present a study of a new glass system: lead–germanium–tellurite glasses in the form of 0.05K2O–0.1ZnO–0.1BaO–0.2PbO–xGeO2–(0.55 - x)TeO2 with x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.55. Differential temperature analysis of this glass system shows that increasing GeO2 content raises the glass transition temperature (Tg) and suppresses the crystallization tendency in a large temperature range from Tg to the glass melting temperature. The maximum vibrational frequency is intermediate between germanate and fluoride glasses, in the range of 750 cm−1 to 820 cm−1. Subsequently, Optical absorption, photoluminescence, and upconversion fluorescence were measured for Yb3+, Er3+ co-doped lead–tellurium–germanate glasses. It was found that the full width at half-maximum of the fluorescence spectrum at 1534 nm decreases and the measured radiative lifetime increases with the replacement of TeO2 by GeO2. Excitation at 976 nm into the glass system leads to an intense green emission and a relatively weak red emission. With the addition of GeO2, the increase of red fluorescence and the decrease of green emission in intensity are due to the increase of nonradiative transition rates between the 4S3/2 and 4F9/2 states of Er3+ ions. The quadratic dependence of the green and red emissions on excitation power indicates that two-photon absorption process occurs in this glass system excited at 976 nm.

Formation and relaxation of paramagnetic centers in GeO2—SiO2 glasses by KrF excimer laser irradiation

Essential reaction induced by KrF laser irradiation in GeO2—SiO2 glasses was the pair generation of electron-trapped centers of Ge ion (GEC) and self-trapped hole (STH) centers of bridging oxygen. The GEC relaxed to GeE’ center during irradiation. This relaxation proceeded quickly with increasing GeO2 content. The concentration ratio of [STH] to [GEC + GeE'] was approximately 1:2. After annealing at room temperature, the majority of STH recombined with GEC (or GeE'). It was considered that the origin of this charge imbalance was the hole transfer from STH to other ions.

D.c. and a.c. electrical properties of vacuum evaporated thin SiO/GeO2 films

The d.c. and a.c. electrical properties were studied for various compositions of SiO/GeO2 co-evaporated thin films carrying aluminium electrodes, in the temperature range 193–413 K. A.c. measurements were made over the frequency range 2x102–106Hz. The value of the d.c. activation energy was found to decrease with increasing GeO2 content in the SiO. In the region of high applied field (above 106 Vm−1, the conduction mechanism is governed by Schottky emission at the blocking contact. The a.c. electrical conductivity, σ(ω), varies with frequency according to the relation σ(ω) ∝ ωs, where the exponent s was found to be dependent on temperature and frequency. The a.c. conduction at low temperature was due to an electronic hopping process. The number of localized sites was estimated from the a.c. measurements for different compositions of SiO/GeO2 using the models proposed by Elliott and by Pollak, and the values are compared. The Elliott model satisfactorily accounts for the observed a.c. electrical results. A correlation was found between activation energy, optical band gap, conductivity and number of localized sites for the various compositions of SiO/GeO2 films. The relative dielectric constant, ɛr, and loss factor, tan δ, were found to increase with the increase of GeO2 content in the films.

Glass Formation and Properties in the System Calcia‐Gallia‐Germania

The critical cooling rate for glass formation, Rc, was measured for four compositions in the system calcia‐gallia‐germania. The activation energy, E, and frequency factor, u, for the crystallization process were determined by reheating the glasses at varied constant heating rates and measuring the temperature of crystallization. Both E and v increased, with increasing germania content of the glass, whereas Rc decreased. The density, refractive index, and Abbe number were also measured; all decreased with increasing GeO2 content. These results are compared with those for calcia‐gallia‐silica glasses of comparable compositions.