Fluoride Glasses Research Articles

Crystallization behavior of hafnium fluoride-based fluorochloride glasses

The crystallization mechanism of chlorine-containing fluorohafnate glasses with the compositions (65–56)HfF4 · (20–x)BaF2 · xBaCl2 · 4LaF3 · (3–y)AlF3 · yInF3 · (5–18)NaF has been studied by X-ray diffraction and differential thermal analysis. The results demonstrate that characteristic features of the glasses are a decrease in glass transition temperature and the precipitation of fine-particle crystalline chloride phases at temperatures below the crystallization temperature of their fluoride analogs. We have studied the effect of the Cl/F ratio in the glass batch and the melt cooling rate on the crystallization behavior of the glasses and determined the heat treatment temperature and time for the formation of transparent glassceramic materials. The luminescence properties of Er3+-doped fluoride and fluorochloride glasses and glassceramics prepared from them have been investigated in the 1.5-µm range.

Enhanced 2.7- and 2.9-μm emissions in Er3+/Ho3+ doped fluoride glasses sensitized by Pr3+ ions

In this report, Er3+/Ho3+/Pr3+ tri-doped fluoride glass was prepared. The enhancement of 2.7 and 2.9μm emissions from Er3+/Ho3+doped system were achieved successfully after the addition of Pr3+. The combination of low OH− concentration, low maximum phonon energy and high mid-infrared transmittance is beneficial to the realization of mid-infrared emissions. The energy transfer mechanism among Er3+, Ho3+ and Pr3+ was investigated. The decay profiles of several levels were measured to further examine the enhanced mid-infrared emissions. Moreover, high stimulated emission cross sections at 2.7- and 2.9μm (1.08×10−20cm2 and 2.0×10−20cm2, respectively) were determined. Er3+/Ho3+/Pr3+ tri-doped fluoride glass might provide a new choice for mid-infrared laser.

Glasses on the basis of heavy metal fluorides

In this review, the information on glass-forming fluoride systems is presented, and the main methods for synthesizing glasses on the basis of fluorides of the metals of Groups I–IV, their physicochemical properties, techniques for producing fibers and areas of application, and the techniques for purifying them from undesired impurities are discussed. Modern materials science studies in the area of fluoride glasses are aimed at searching for glasses activated with rare-earth elements (REEs) with a broad IR transmission range and high optical homogeneity with the purpose of creating efficient active optical media in a wide spectral range, as well as converters of IR radiation into the visible range for enhancing the efficiency of solar cells and exciting photocatalysts. The analysis of the influence of impurities on the optical transparency, crystallization, and phase purity of the glasses under study is presented. The methods for the deep purification of the initial substances for preparing fluoride glasses with the minimum content of impurities are considered. Original procedures for synthesizing fluorides of elements and glasses free from oxygen-containing impurities are created on the basis of physicochemical studies of the interactions of fluorinating agents with the components of fluoride glasses.

Elasticity, deformation and fracture of mixed fluoride–phosphate glasses

Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) as a more stable alternative to fluoride glasses. Benefitting from the low polarizability of the fluoride anion, high electronic band-gap and low phonon energy, they present one of the most important host species for the inclusion of rare-earth and other optically active dopants into fiber and bulk glass. A major limitation, however, has been the mechanical performance of these glasses and their susceptibility to damage and fracture. Here, we provide comprehensive data on elasticity, plasticity and fracture of a series of mixed fluoride–phosphate glasses with strongly ionic bonding character, spanning the compositional join of strontium metaphosphate and alkaline earth aluminum fluoride.Simplistic models such as that of Makishima and Mackenzie can reproduce the mechanical properties of these glasses within a limited compositional range. This break-down is explained in the context of glass structure, in particular, the role of intermediate VIAl3+ species which act as bridges between the fluoride and the phosphate sub-networks. A simple binominal model is implemented to estimate the atomic fractions of aluminum as well as of magnesium cations, which are linked to two or more phosphate units, and used as an indicator for the connectivity between the anion sub-networks. Such adjustment of the Makishima–Mackenzie model provides an unambiguous rational for the elastic properties, but also for the susceptibility to inelastic deformation and fracture of FP glasses.

In-amplifier mid-infrared supercontinuum generation.

Mid-infrared supercontinuum (SC) generation from 2.6 to 4.1 μm is demonstrated in a single-mode erbium-doped fluoride glass fiber amplifier pumped at 976 nm and seeded by an optical parametric generation (OPG) source emitting 400 ps pulses at 2.75 μm. Up to 82% of the SC power is generated beyond 3 μm. This novel and simple in-amplifier SC generation approach is promising for the development of compact and efficient sources operating in the mid-infrared, especially in the 3-5 μm band.

Long fluorescence lifetime and broad bandwidth of 2.7 μm emission from Er3+ doped fluoroaluminate–tellurite glass

In this paper, fluoroaluminate–tellurite glasses were fabricated by introducing TeO2 into the fluoroaluminate glass. The thermal stability of the fluoroaluminate–tellurite glass as a function of the TeO2 concentrations were investigated by differential scanning calorimetry (DSC). The 2.7μm emission of Er3+ ions in fluoroaluminate–tellurite glass was investigated: τ can reach to 1.34ms and emission bandwidth is more than 150nm. In conclusion, fluoroaluminate–tellurite glass is proposed to be a promising material for 2.7μm fiber lasers.

Cryogenic Tm:YAG Laser in the Near Infrared

Thulium laser operation on the 3H4–3H6 transition at 823 nm has been demonstrated in bulk Tm:YAG by quasi-continuous-wave pumping with a fiber-coupled diode array at 782 nm. The prior demonstrations of this laser transition have been limited primarily to fluorozirconate glass host materials in waveguide configurations. Population trapping has been identified as an important consideration in the design and operation of lasers on this transition. The use of a crystalline host should enable both high peak and average power operation, and the basic principles discussed in this paper should be extensible to other crystalline hosts and room-temperature operation.

Ho³⁺/Er³⁺ co-doped fluoride glass sensitized by Tm³⁺ pumped by a 1550 nm laser diode for efficient 2.0 μm laser applications.

In the present Letter, a high-emission intensity of 2.0 μm is reported for Ho(3+)/Er(3+) co-doped fluoride glass sensitized by Tm(3+) ions under 1550 nm excitation. The measured absorption spectra do not show clustering in the local ligand field, which also demonstrates that Er(3+) ions are efficiently excited by pumping and energy transfer (ET) to Ho(3+) and Tm(3+) ions. The enhanced Ho(3+):2.0 μm emission has a maximum emission cross section (4.8×10(-21) cm(2)). An ET mechanism based on the enhanced 2.0 μm emission and other reduced near-infrared emissions is discussed. Results show that the addition of Tm(3+) ions populates the Ho(3+):(5)I(7) level through the channel at the Tm(3+):(3)F(4) level between Er(3+) and Ho(3+) ions. The spectroscopic characteristics and thermal property of Er(3+)/Ho(3+)/Tm(3+) tri-doped ZBYA glass reveal that the material is an attractive host for 2.0 μm lasers.

Glass formation in niobium fluoride systems

Various variants of producing niobium fluoride glasses using niobium pentafluoride and its oxyfluoride compounds as precursors were studied.

Study of Fluoride Glasses Devitrification-Based Magnesium

The kinetics of devitrification of fluoride glasses stabilized by magnesium fluoride when heated for some time between the glass transition and melting temperatures. The crystallization kinetics of AlF 3 -YF 3 -PbF 2 -CdF 2 -MgF 2 glass prepared by melting the halide powders were studied by differential scanning calorimetry (DSC). The heating rate varied between 2 and 10 Kmim -1 . Arami’s exponent (n) obtained by a non-isothermal method was 1.5 and 2.5 for a AlF 3 -YF 3 -PbF 2 -CdF 2 -xMgF 2 (x= 0, 5, 10) and n > 2.5 for a AlF 3 -YF 3 -PbF 2 -CdF 2 -15MgF 2 . According to the classical interpretation of n, these magnitudes correspond to diffusion controlled growth of crystals. The activation energies for crystallization, (E), varied from 195-326 KJ/mol. These results confirm the improved stability of these glasses, which could be used as base glasses for low phonon energy fluoride glass fibers. Keywords: crystallization kinetics, glass transition, DSC, Avrami’s exponent (n), activation energies (E).

Spectroscopic properties and energy transfer mechanism in Dy3+/Tm3+ codoped fluoroaluminate glasses modified by TeO2

This paper investigates 2.9μm emission properties and energy transfer processes in the Dy3+/Tm3+ codoped fluorotellurite glass. The measured absorption spectra demonstrate that the codoped sample can be efficiently pumped by an 800nm excitation. Judd–Ofelt and radiative parameters are calculated and discussed. Higher spontaneous emission probability (39.6S−1) provides a better probability to obtain laser action. Obvious 2.9μm emission of Dy3+: 6H13/2→6H15/2 transition is observed after codoping with Tm3+ and the optimum ratio in this system is 1:1. Energy transfer processes between the two ions are discussed and the related microscopic interaction parameters are calculated. Hence, these results indicate that the Dy3+/Tm3+ codoped fluorotellurite glass is a suitable material for developing solid state laser at approximately 3.0μm.

Glass forming ability and enhanced 2.7 μm emission of erbium ions in TeO2 doped fluoroaluminate glass

New fluoroaluminate–tellurite glasses were fabricated by introducing TeO2 into the fluoroaluminate glass. The glass-forming ability and crystallization kinetic parameter kD(T) of the fluoroaluminate–tellurite glass system as a function of the TeO2 concentrations were investigated by differential scanning calorimetry (DSC). Also, the crystalline phases were determined by X-ray diffraction (XRD). X-ray diffraction showed that the sample without TeO2 composition had some crystallization phases when the glass was reheated. However, the addition of TeO2 changed the crystallization ability and improved the glass forming ability of the fluoroaluminate glass. Besides, 2.7μm emission properties were investigated through the measured emission spectra. Enhanced 2.7μm emission was observed in the fluoroaluminate–tellurite glass under 980nm excitation and the calculated emission cross section (σe) was larger than some reported values. This kind of fluoroaluminate–tellurite glass with excellent glass-forming ability and emission properties could be used as host material for optical fiber and 2.7μm lasers.

Near infrared ultrafast pump-probe spectroscopy with ZrF4-BaF2-LaF3-AlF3-NaF fiber supercontinuum

We report on the performance of a setup designed for femtosecond pump-probe spectroscopy in the near infrared (NIR) spectral region. We generate a supercontinuum (SC) probe by coupling 140 fs light pulses at 1550 nm into a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The combined high nonlinearity and transparency of the ZBLAN fluoride glass allows us to obtain a SC probe from 1 to 2.6 μm. The NIR pulses are used to demonstrate a proof of principle experiment probing the relaxation of photo induced excitations in a conjugated polymer:fullerene blend film. The results show the possibility to perform fibre based NIR SC femtosecond spectroscopy at >100 KHz repetition rate and using lasers with pulse energy just above 300 nJ.

Femtosecond fiber lasers reach the mid-infrared

Ultrafast fiber lasers operating in the near-infrared have revolutionized laser science by enabling numerous breakthroughs in both fundamental science and industrial applications. In this Letter, we extend the spectral coverage of these laser sources to the mid-infrared by reporting the first femtosecond fiber laser operating near 3 μm. This passively mode-locked fiber ring laser based on nonlinear polarization evolution in an Er3+-doped fluoride glass fiber generates 207 fs pulses at 2.8 μm with an estimated peak power of 3.5 kW. This demonstration paves the way for further developments of promising applications in the molecular fingerprint region such as frequency comb spectroscopy.

30 W fluoride glass all-fiber laser at 2.94 μm.

We report the demonstration of a 2938 nm erbium-doped fluoride glass fiber laser delivering a record output power of 30.5 W in continuous wave operation. The passively cooled all-fiber laser cavity based on intracore fiber Bragg gratings has an overall laser efficiency of 16% as a function of the launched pump power at 980 nm and a single-mode output beam quality of M2<1.2. This power scaling demonstration of a fiber laser operating near the vibrational resonance of water is likely to have a significant impact on several biomedical applications.

Insufficient evidence that slow-release fluoride devices reduce caries.

Cochrane Oral Health Group's Trials Register, Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase, US National Institutes of Health Trials Register and World Health Organisation (WHO) International Clinical Trials Registry Platform. Parallel randomised controlled trials (RCTs) of any type of slow-release fluoride device irrespective of publication status, language or blinding were considered. Split mouth studies were excluded. Standard Cochrane methods were followed with at least two reviewers independently undertaking all the key steps. Only one trial which was considered to be at high risk of bias was included. The trial included 174 children with 132 available for two year examination. However statistical analysis was performed on only the 63 children (31 in intervention group, 32 in control group) who had retained the beads (retention rate was 47.7% at two years). Among these 63 children, caries increment was reported to be statistically significantly lower in the intervention group than in the control group (DMFT: mean difference -0.72, 95% confidence interval (CI) -1.23 to -0.21; DMFS: mean difference -1.52, 95% CI -2.68 to -0.36 (very low quality evidence)). Although this difference was clinically significant, it only holds true for those children who retained the fluoride beads; over 50% of the children did not retain the beads. Adverse effects were not reported. There is insufficient evidence to determine the caries-inhibiting effect of slow-release fluoride glass beads. The body of evidence available is of very low quality and there is a potential overestimation of benefit to the average child. The applicability of the findings to the wider population is unclear; the study had included children from a deprived area that had low levels of fluoride in drinking water, and were considered at high risk of carries. In addition, the evidence was only obtained from children who still had the bead attached at two years (48% of all available children); children who had lost their slow-release fluoride devices earlier might not have benefited as much from the devices.

Spectroscopic properties of the glass of fluoroaluminate systems with small additives of barium metaphosphate activated with the ions of rare-earth elements

Optical and EPR studies of fluoroaluminate glass based on usovite with small additives of barium metaphosphate (0.1–10 mol %) have been performed. The introduction of phosphates in the composition of the fluoride matrix of glass leads to a decrease in the crystallization ability but to the simultaneous shift of the edge of the transmission band into the high-energy spectral region. It was shown that for compositions with 1–2 mol % of barium metaphosphate this shift does not exceed 125 cm−1 at a transmission of not less than 60% to 1430 cm−1 (6.4 μm) for the samples with the thickness of 1 mm. It is supposed that glass containing 1.5–2.0 mol % Ba(PO3)2 is characterized by the mixed frame of glass different from the chain structure of fluoroaluminate and phosphate glass.

Observation of Midinfrared 4-$\mu \text{m}$ Emission in Ho3+-Doped Fluoroaluminate Glasses

Ho3+ activated fluoroaluminate glasses were prepared successfully via melt-quenching method. Not only 2- and 2.85- $\mu \text{m}$ emissions but also 4- $\mu \text{m}$ emissions were observed for the first time by 900-nm Ti: sapphire laser pumping. The optimal midinfrared emissions were obtained when Ho3+ concentration reaches 1 mol%. Spectroscopic properties and energy transfer mechanism of Ho3+ were investigated in detail. Results indicate that the prepared glasses possess high midinfrared transmittance (90%), large emission cross sections at $2~\mu \text{m}$ ( $7.6 \times 10^{-21} $ cm $^{2}$ ), $2.85~\mu \text{m}$ ( $17.6 \times 10^{-21}$ cm $^{2}$ ), and 4 $\mu \text{m}$ ( $6.87 \times 10^{-21}$ cm $^{2}$ ) together with superior gain properties. It is suggested that Ho3+ activated fluoroaluminate glass is an attractive candidate for midinfrared laser materials application.

Site selection spectroscopy in Eu3 +-doped lanthanum fluorozirconate glass and glass-ceramic

The optical properties of Eu3+-doped glass and transparent glass-ceramic with composition (in mol%) 70.2ZrF4–23.4LaF3–0.6AlF3–5.8GaF3 were investigated by site selective spectroscopy in order to study the effect of ceramization on the symmetry of Eu3+ sites. The glass-ceramic obtained after thermal treatment of the glass ZLAG contains a unique crystalline phase of unknown structure. The analysis and comparison of FLN spectra in these materials are presented and different classes of sites are discussed. We found the presence of two main site distributions for Eu3+ ions of equivalent symmetry (C2v or lower) in the glass and two sites of different symmetry (C2v or lower and C4v or lower) in the glass-ceramic (GC). The estimated average crystal field strength for glass and GC decreases with the 5D0→7F0 energy. The results suggest that the two kinds of sites identified in the glass correspond to Eu3+ ions in and out of the former network. Decay-time measurements of 5D0 level of Eu3+ evidenced energy transfer between high and low energy sites and showed an increase of lifetime from the glass to the glass-ceramic.

Downconversion in Pr3+–Yb3+ co-doped ZBLA fluoride glasses

Fluorozirconate ZBLA glasses with molar composition 57ZrF4–34BaF2–5LaF3–4AlF3–0.5PrF3–xYbF3 (from x=0 to 10) were synthesized to evaluate the rate of the conversion of visible photons into infrared photons. The emission spectra in the near infrared (NIR) at 950–1100nm and the luminescence decays in the visible and NIR indicate an energy transfer from Pr3+ to Yb3+ upon blue excitation of Pr3+ at 440nm. The energy transfer efficiency increases with Yb3+ concentration to reach 86% with 0.5Pr3+–10Yb3+ co-doping (in mol%). However, the quenching of the Yb3+ emission strongly reduces the efficiency of the downconversion process: the decay time values decrease from 600µs (x=0.5mol%) to 85µs (x=10mol%).