Heavy Metal Fluoride Glasses Research Articles

Heavy metal fluoride glasses: A tutorial review

Heavy metal fluoride glasses are the backbone of modern mid-infrared fiber technology. In the last few years, optical fibers made of fluorozirconate, fluoroaluminate, and fluoroindate glasses have reached the high level of reliability that is required for their widespread use in industrial and medical applications, which explains the rapid growth of this technology. In this tutorial review, the author, who was part of the team that discovered heavy metal fluoride glasses exactly fifty years ago, provides a summary of the glass synthesis process and elucidates the most important physical properties of heavy metal fluoride glasses. Finally, a brief overview of their main application areas is presented.

The Experimental Investigation of Kinetics of Glass Transition of ZBLAN Glass by using Differential Scanning Calorimetry

A ZBLAN glass is a heavy metal fluoride (HMF) glass that possesses high thermal stability and excellent property as atransmitting material. The current study examines the thermal properties of ZBLAN glass utilizing Differential scanningcalorimetry (DSC) at various heating rates. The temperature of glass transition, Tg, is observed to vary with heating rate,indicating its kinetic nature. Through the use of Kissinger's and Augis- Bennett's methodologies and the heating ratedependency of Tg, the activation energy (E) has been determined. These methodologies have also been used to obtain thefragility index (m), which can be used to evaluate the glass forming ability (GFA) of the system. The fragility index found isgreater than 16, indicating that the ZBLAN glass is "fragile."

Reconstruction and modeling of the complex refractive index of nonlinear glasses from terahertz to optical frequencies.

The linear complex refractive index of a set of borosilicate and tellurite as well as heavy metal oxide silicate, germanate and fluoride glasses has been determined using the Kramers-Kronig analysis on combined data from terahertz time domain (THz-TD) and Fourier transform infrared (FTIR) spectrometers in the ultrabroadband range of 0.15 THz to 200 THz. Debye, Lorentz and shape language modeling (SLM) approaches are applied. Far-infrared absorption power-law model parameters are determined via searching for the largest frequency range that minimizes the root mean squared error (RMSE) of a linear least squares fit for the set of glasses and other glass literature data. Relationships between the absorption parameters, glass properties and compositions are explored.

Suppression of crystallization in ZBLAN glass by rapid heating and cooling processing

AbstractZBLAN glass is a heavy metal fluoride glass that tends to undergo heavy devitrification, resulting in a crystalline material. It has many applications, including its use as an optical waveguide for fiber‐optic technology. However, when the glass is processed with traditional casting techniques, crystallites form readily that act as scattering centers, which results in large attenuation losses. In this study, it has been experimentally demonstrated that processing ZBLAN rapidly with a heating rate of 25 000 K/min and cooling rate of 4000 K/min yields test samples that are fully amorphous and retain a disordered molecular arrangement characteristic of its molten state. This novel method was developed using a specifically designed equipment named a Rapid Electro‐thermal Processing Device, or “REPD.” The REPD applies ohmic heating and thermal conduction to a heat sink to rapidly process the ZBLAN material. The absence of crystallites in the rapidly processed ZBLAN test samples were verified using transmission electron microscopy (TEM) analysis. Applying a theoretical algorithm, the critical cooling rate for yielding fully amorphous ZBLAN glass was determined to be 1081 K/min for a sample volume of 9.4 × 10−8 m3.

Suppression effects of cooling rate on crystallization in ZBLAN glass

ZBLAN glass is a heavy metal fluoride glass that shows great potential in the application of long-haul telecommunication cables. However, during processing in the fiber-drawing temperature region, the material tends to undergo heavy devitrification, resulting in a crystalline fiber that is not usable as an optical waveguide. In this study, ZBLAN glass was processed with different cooling rates to discern how the rate of cooling affects the process of crystallization. Rapidly cooled ZBLAN glass test samples were then analysed with a wide range of spectroscopy and imaging techniques including EDS, SEM, TEM and XRD. These techniques revealed there are two predominant crystal phases, one rich in zirconium and barium, the other in zirconium and sodium. Ultimately, a critical cooling rate was established to be somewhere between 900°C/min and 4000°C/min, with a theoretically predicted value of 1081°C/min for a test sample volume size of 9.4×10−8m3. Cooling above this critical cooling rate yielded fully amorphous ZBLAN test samples that were completely free of nano-crystalline inclusions. Using Kramers-Kronig relations, an attenuation loss for the fully amorphous ZBLAN test samples was estimated to be 0.09dB/Km at a wavelength of 1800nm.

GLASSY MATERIALS AND LIGHT: PART 1

2015 is the Year of Light, according to UNESCO. Chemistry has a close relationship with light and one of the materials that allows such synergy is glass. Depending on the chemical composition of the glass, it is possible to achieve technological applications for the whole range of wavelengths extending from the region of the microwave to gamma rays. This diversity of applications opens a large range of research where chemistry, as a central science, overlaps the fields of physics, engineering, medicine, etc., generating a huge amount of knowledge and technological products used for humanity. This review article aimed at discussing some families of glasses, illustrating some applications. Due to the extension of the theme, and all points raised, we thought it would be good to divide the article into two parts. In the first part we focus on the properties of heavy metal oxide glasses, fluoride glasses and chalcogenide glasses. In the second part we emphasize the properties of glassy thin films prepared by sol-gel methodology and some applications, of both glasses as the films in photonics, and more attention was given to the nonlinear properties and uses of photonic fibers.

Purification of fluorides for optical materials synthesis

This paper considers processes for the ultrapurification of starting materials for the preparation of heavy metal fluoride glasses with the lowest possible impurity content. Based on the results of physicochemical studies of reactions between fluorination agents and components of fluoride glasses, we have proposed novel techniques for the preparation of fluorides and glasses free of oxygen-containing impurities.

2.7 μm Emission properties of Er3+ doped fluorozirconate glass

Fluorozirconate glass, considered as the most stable heavy metal fluoride glass and excellent host for rare earth ions, has been extensively used for 2.7 μm laser materials due to its low intrinsic loss, wide transparency window, and small phonon energy. In this paper, a novel erbium ion doped fluorozirconate glass was prepared, 2.7 μm emission properties, thermal stability and Raman spectra were investigated and the spontaneous transition probability and branching ratio were calculated and analyzed. It was found that the thermal stability was greatly improved due to the ΔT increased from 59 to 89°C after introducing YF3 on the basis of ZBLA(ZrF4-BaF2-LaF3-AlF3). In addition, intensive 2.7 μm emission was observed and the present sample with the addition of Y3+ possessed larger 2.7 μm emission cross section (1.12 × 10−20 cm2) which indicated that this kind of fluoride glasses could potentially be used as an efficient gain media in the 2.7 μm fiber laser system.

Eliminating Crystals in Non-Oxide Optical Fiber Preforms and Optical Fibers

Non-oxide fiber optics such as heavy metal fluoride and chalcogenide glasses are extensively used in infrared transmitting applications such as communication systems, chemical sensors, and laser fiber guides for cutting, welding and medical surgery. The addition of rare earths such as erbium, enable these materials to be used as fiber laser and amplifiers. Some of these glasses however are very susceptible to crystallization. Even small crystals can lead to light scatter and a high attenuation coefficient, limiting their usefulness. Previously two research teams found that microgravity suppressed crystallization in heavy metal fluoride glasses. Looking for a less expensive method to suppress crystallization, ground based research was performed utilizing an axial magnetic field. The experiments revealed identical results to those obtained via microgravity processing. This research then led to a patented process for eliminating crystals in optical fiber preforms and the resulting optical fibers. In this paper, the microgravity results will be reviewed as well as patents and papers related to the use of magnetic fields in various material and glass processing applications. Finally our patent to eliminate crystals in non-oxide glasses utilizing a magnetic field will be detailed. Keywords: Microgravity, magnetic field, non-oxide glass, crystallization

Investigation on the Spin Hamiltonian Parameters and the Local Structures for Cu2+ Centers in Sodium Phosphate and Heavy Metal Fluoride Glasses

The spin Hamiltonian parameters (the anisotropic g factors gII, g⟂ and hyperfine structure constants AII, A⟂) for the Cu2+ sites in sodium phosphate glasses Na2O-9P2O5 and heavy metal fluoride glasses 60ZrF4-5LaF3 -20BaF2-15NaF are theoretically investigated by using the high (fourth-) order perturbation formulas of these parameters for a 3d9 ion in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt, are taken into account by considering the relative axial elongation of the ligand octahedron around the Cu2+ due to the Jahn-Teller effect. According to the calculations, the ligand octahedra around Cu2+ are suggested to suffer about 12% and 18% relative elongation along the C4-axis for the studied Na2O-9P2O5 and 60ZrF4 -5LaF3-20BaF2 -15NaF glasses, respectively. The local structures characterized by the above axial elongations are discussed

High-Power ZBLAN Glass Fiber Lasers: Review and Prospect

ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), considered as the most stable heavy metal fluoride glass and the excellent host for rare-earth ions, has been extensively used for efficient and compact ultraviolet, visible, and infrared fiber lasers due to its low intrinsic loss, wide transparency window, and small phonon energy. In this paper, the historical progress and the properties of fluoride glasses and the fabrication of ZBLAN fibers are briefly described. Advances of infrared, upconversion, and supercontinuum ZBLAN fiber lasers are addressed in detail. Finally, constraints on the power scaling of ZBLAN fiber lasers are analyzed and discussed. ZBLAN fiber lasers are showing promise of generating high-power emissions covering from ultraviolet to mid-infrared considering the recent advances in newly designed optical fibers, beam-shaped high-power pump diodes, beam combining techniques, and heat-dissipating technology.

Fabrication of heavy metal fluoride glass, optical planar waveguides by hot-spin casting

Hot-spin casting is further investigated using a customised rig for making optical planar waveguides from inorganic-compound-glasses. The rig enables a controlled mass of core-glass, held above its liquidus, to be gravity-cast onto the top surface of a spinning cladding-glass substrate that has been pre-heated to around its glass transformation temperature. Spinning encourages the cast liquid to spread as a film over the top surface of the glass substrate. The mass of liquid cast is controlled by the timed opening of an orifice in the base of the core-glass melt-crucible. The resulting step index, slab optical waveguides are annealed, then cooled to room temperature; they comprise a higher refractive index, glass film core, on top of a lower refractive index glass substrate cladding. The glass film core is air-clad. at its upper surface. The process is applied to two heavy metal fluoride core/clad. glass pairs, namely ZBLANPb/ZBLAN and ZBLALiYPb/HBLANY (where ZBLANLiYPb is ZrF 4–BaF 2–LaF 3–AlF 3–LiF–YF 3–PbF 2 and H is HfF 4) to give waveguides of small and large numerical aperture (NA) (e.g. at 643.8 nm wavelength, NA is 0.18 and 0.33, respectively). The Hot-Spin-Cast waveguides exhibit a guiding region whose top surface tends to be parallel to the upper surface of the underlying substrate. However, flatness of the top surface of the guiding region is limited by the flatness of the top surface of the underlying substrate. Multimode slab waveguiding is demonstrated for both NA waveguide types for glass film cores of depths ⩾10 μm.

Effects of chloride substitution on the chemical and physical properties and the crystallization behavior in heavy metal fluoride glasses

Effect of the substitutions of chloride for fluoride on the chemical and physical properties and the crystallization behavior in heavy metal fluoride glasses has been investigated. The characteristic temperature of the glass does not changed obviously when the fluoride was taken place by chloride. Compared with samples of being free of ErF 3, the doping samples are more inclined to be surface crystallization. Optical basicity in the glass system increases with increasing the negative charge provided by the chloride atoms and the absorption peak red shifted is observed in absorption spectra. XRD measurements show that not a single crystalline phase appears in the heated glass samples, which indicate the substitutions of chloride for fluoride with a variety of crystalline precipitation trends.

Lithium self-diffusion in some heavy metal fluoride glasses

Li self-diffusion has been studied below T g in a series of ZrF 4–BaF 2–LaF 3–LiF glasses with LiF contents of 10, 20, and 30 mol%, respectively. The D Li ∗ values range between about 10 −12 and 10 −15 cm 2/s and increase with increasing LiF content from 10 to 20% by two orders of magnitude. The stable isotopes 6Li (enriched) and 7Li and an SNMS depth profiling were used. For the precision of the diffusion data an anhydrous vacuum deposition of the 6Li tracer on the highly reactive glass surfaces was essential. In the glass with 30 mol% LiF no Li mobility could be determined yet with the present diffusion method. The Li diffusion is discussed and it is tried to understand why it displays a differing behaviour compared to that of the Na diffusion in respective NaF-containing glasses.

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na +–Li + ion exchange, electrical conductivity, and mechanical relaxation have been studied below T g on glasses of the system ZrF 4–BaF 2–LaF 3–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na +–Li + ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F − and Li + ions to the transport. Moreover, the presence of the three partially interacting mobile species F −, Na +, Li + obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li + transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li + movement via energetically suitable sites near F − ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.

Spectroscopic study of Eu3+ ions in heavy metal fluoride and oxide glasses

AbstractTwo types of fluoride and oxide systems belonging to the heavy metal glass family have been studied. From absorption and emission spectra together with Judd–Ofelt analysis, spectroscopic parameters of Eu3+ ions in both optical systems were evaluated and compared. The new oxide glassy system based on PbO–B2O3–Al2O3–WO3 exhibits interesting spectroscopic properties of Eu3+ ions for application as a red‐emitting optical material. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of thermal treatment on spectroscopic properties of Er 3+ ions in multicomponent InF 3-based glasses

The heavy metal fluoride glasses based on InF 3 and doped with 2 mol% of ErF 3 were obtained as amorphous material. In order to obtain glass-ceramics, as-melted samples were annealed at various temperatures and times. The changes of the erbium spectroscopic properties in the multicomponent fluoride system are discussed as a function of thermal treatment. The multi-step mechanism of crystallization has been analyzed by spectroscopic analysis and compared with the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data.

Spectroscopic analysis of praseodymium and erbium ions in heavy metal fluoride and oxide glasses

Spectroscopic analysis of Pr 3+ and Er 3+ ions in fluoride and oxide systems belonging to the same heavy metal glass family has been reported. From absorption and emission spectra using Judd–Ofelt theory various spectroscopic parameters like radiative transition rates, luminescence lifetimes, radiative quantum efficiencies, spectral line widths as well as emission cross-sections are determined. Selected examples for the spectroscopic behavior of both optical glasses are discussed in relation to the practical application of these materials as a potential laser-active media in the visible and infrared spectral region.

Effects of high-energy electron irradiation on heavy-metal fluoride glass

The effects of high-energy (100keV) electron irradiation have been observed in a heavy-metal fluoride glass using in situ time-resolved electron energy loss spectroscopy in a scanning transmission electron microscope. Formation of F2 has been observed. The irradiation-induced changes of configuration and composition are discussed based on the evolution of the near-edge fine structures of F K edge. We suggest that the high sensitivity to electron irradiation is due to the existence of nonbridging F in heavy-metal fluoride glasses so that is there is a tendency of the electron irradiation to eliminate nonbridging F in the irradiated region.

The Study of Devitrification Processes in Heavy‐Metal Fluoride Glasses

Heavy-metal fluoride glasses are very promising optical fiber materials because of their predicted ultralow loss and long transparency range. Although conventional silica fibers have attained their theoretical minimum loss of 0.15 dB/km, fluoride glasses have the potential to yield losses of only 0.001 dB/km. Fluoride glasses also exhibit transparency into mid-IR frequencies, a region inaccessible to silica fibers. However, this group of glasses is very unstable to devitrification during both bulk glass synthesis and fiber-drawing. This instability has limited their commercial exploitation to a small niche market in the laser industry. The ZBLAN glass (53ZrF(4)-20BaF(2)-4LaF(3)-3AlF(3)-20NaF) is the most promising of these materials since its fiber-drawing region lies on the edge, or possibly just outside its crystallization region. It is believed that additional research into understanding the nucleation mechanics involved in the devitrification of fluoride glasses will lead to the development of technology to suppress such nucleation, or at least minimize the associated crystallization temperature region, allowing high optical quality fibers to be produced. It has recently been demonstrated that a microgravity environment can suppress devitrification in ZBLAN glass preform preparation, and that devitrification may be reduced when preparing ZBLAN terrestrially in a containerless facility. It is believed that the role of viscosity is critical in the devitrification mechanism of ZBLAN glass and in determining the optimum fiber-drawing temperature. Unfortunately, viscosity data for fluoride glasses are only available above the melting point and around the glass transition. A piezoelectric viscometer has been developed and is being used to determine the missing viscosity data in the fiber-drawing and crystallization temperature regions. Shear thinning of the glasses and/or the application of hydrostatic pressure on the glasses have been recently proposed to be responsible for devitrification during fiber-drawing at 1 g and in reduced gravity. The study we report here is to explore the extent to which such a proposal is realistic.