Ion implantation effects in heavy metal fluoride glasses

Samples of a heavy metal fluoride glass (BInZnYbTGa) were subjected to argon and nitrogen irradiations of energies of 50 and 100 keV and fluences of 5×10¹⁶ and 1×10¹⁷ ions/cm². A 10 keV Ar irradiation at the ion dose of 1×10¹⁷/cm² was also performed. Modifications induced by the implants were characterized by nuclear microanalysis, electron spectroscopy, scanning electron microscopy and optical techniques. Surface precipitation of Th and Ba, as well as F and In depletion, were detected. Correlated modifications of the optical transmittance and reflectance were observed.     

Effect of dehydration techniques on the fluorescence spectral features and OH absorption of heavy metals containing fluoride tellurite glasses

Heavy metal containing fluoride tellurite glasses were prepared by different dehydration techniques and the effects of dehydration techniques on fluorescence spectral features, OH content and volatilization of the glass compositions were systematically studied by means of fluorescence spectral measurements FTIR and energy-dispersive X-ray spectrometer. Experimental results indicated that different dehydration induced difference in actual compositions of the glasses that resulted in the variation of their fluorescence spectral features, and melting the glass frits in close environment with mechanical stirring and simultaneous bubbling dry O₂ + CCl₄ mixture in a O₂-rich environment was much more effective to remove the OH groups in the glass matrix, through which an OH absorption coefficient and absorption concentration could be efficiently reduced to as low as 1.09 cm^? 1 and 1.17 × 10¹⁹ cm^? 3, respectively. The low OH content contributed to the increase in fluorescence lifetime, and resulted in the improvement of gain characteristic. The bubbling time of dry O₂ + CCl₄ mixture was optimized via OH absorption concentration investigation.     

The influence of glass composition on the crystal growth kinetics of heavy metal fluoride glasses

The kinetics of crystallization of two heavy metal fluoride glasses, ZrF₄---BaF₂---LaF₃---AlF₃---LiF and ZrF₄---BaF₂---LaF₃---AlF₃---LiF---PbF₂, which are of potential use as core and clad materials for fiber optic waveguides, have been studied by differential scanning calorimetry. The devitrification processes follow the Johnson-Mehl-Avrami relation, and the values of the kinetic parameters for isothermal and non-isothermal techniques are in excellent agreement. The crystallization activation energies for these glasses are about two-thirds those previously reported for a ternary ZrF₄---BaF₂---LaF₃ glass. The implications of the experimental results for glass stability against devitrifications are discussed.     

Radiation-induced defects in fluoride glasses

Fluorozirconate (ZBLA) and fluorohafnate (HBL) glasses have been exposed to ionizing radiation at room temperature, and the resulting defects have been characterized using optical absorption and electron spin resonance techniques. Prominent absorption bands were found to peak in the ultraviolet at 290 nm for the ZBLA glass and at 240 and 310 nm for the HBL glass. Two major electron spin resonance spectra having g values of 1.883 and 2.043 were induced in the HBL glass. Similar electron spin resonance spectra were found in the ZBLA glass. A third spectrum with a g value of 2.008 was also observed in the ZBLA material. The optical and electron spin resonance spectra in these glasses thermally annealed between room temperature and 300°C. Possible models for the defects are discussed.     

Relaxation in mixed alkali fluoride glasses

We have investigated the dynamics of alkali cations as well as fluorine anions in non-oxide fluoride glasses with a total alkali fluoride content varying from 16 to 35 mol% in the frequency range from 10 Hz to 2 MHz and in the temperature range from room temperature to just below the glass transition temperature. We have shown that the dc and ac conductivity, crossover frequency and conductivity relaxation frequency exhibit a minimum in mixed alkali fluoride glasses, where anions also participate in the diffusion processes in addition to cations, unlike mixed alkali oxide glasses and crystals. We have observed lower dimensionality of the conduction pathways in mixed alkali fluoride glasses compared to that in the single alkali glasses. We have shown that the relaxation dynamics in mixed alkali fluoride glasses is independent of temperature.     

Crystallization kinetics of fluoride nanocrystals in oxyfluoride glasses

Oxyfluoride glasses containing different alkaline earth fluoride (CaF₂, SrF₂, and BaF₂) were prepared and their crystallization behavior was analyzed using non-isothermal kinetics based upon differential scanning calorimetry (DSC) scan results. The glass containing CaF₂ showed the fastest kinetics for CaF₂ crystallization, while that containing BaF₂ showed the slowest kinetics for BaF₂ crystallization. On the other hand, all the oxyfluoride glasses showed very similar behavior in the crystallization of glass matrices. The difference in the crystallization behavior of the oxyfluoride glasses was discussed based upon the difference in the size of alkaline earth ions and the difference in the dissociation energy of alkaline earth-fluorine bonds.     

Yellow-to-blue frequency upconversion in Pr-doped aluminium fluoride glasses

Rare-earth-doped fluoride glasses are attractive materials for photonics, since they combine a transmission region from ultraviolet to infrared and low vibrational cut-off energy. We report on the spectroscopic properties of aluminium fluorophosphate glasses doped with 0.1, 0.6, 1, 3 and 10 mol% Pr³⁺. Yellow-to-blue upconversion was observed upon pulsed and continuous-wave (CW) excitation at 575 nm. The temporal evolution of the upconverted fluorescence is characterised by rise and decay times depending on Pr³⁺ concentration. The upconversion intensity has a quadratic dependence on incident pump power, indicating a two-step process. The upconversion emission is described in the framework of a two-ion energy transfer mechanism. Emission in the second telecom window (1.3 μm) was measured upon excitation at 976 nm.     

Optical absorption study on radiation damage in fluoride glasses

The effect of 1.7 MeV electrons on the coloration of fluorozirconate (ZBL) and fluorohafnate (HBL) glasses has been investigated. Irradiation can produce intense broad absorption bands at 325 nm and 253 nm in the glasses. However, the size and shape of the absorption bands in zirconate-based glass (ZBLA) which has Al³⁺ ions as network stabilizers is different from those in ZBL and HBL glass. The optical absorption bands due to self-trapped hole centers can be assigned from dichroic absorption measurements. It appears that the radiolysis damage mechanism may contribute to the coloration of these fluoride glasses.     

Reflection spectra of various kinds of oxide glasses and fluoride glasses in the vacuum ultraviolet region

Reflection spectra of silicate, borate, phosphate, fluorophosphate and fluoride glasses are studied in the spectral region of 2–13 eV in order to understand their dispersion behaviors in the visible region from the point of view of atomic structures.The absorption bands due to bridging oxygen ions or fluorine ions are found at 11.6 eV and 10.4–9.5 eV in silicate glasses, at 10.2 and 8.8 eV in borate glasses, at 9.5 eV in phosphate glasses, at 11.2 eV in fluorophosphate glasses and at 11 eV in fluorozirconate glasses.In silicate glasses, the bands due to nonbridging oxygen ions are found in the region 8.8-4.9 eV. They shift to lower energies with increasing ionic radius, in the order of Ca²⁺, Sr²⁺ and Ba²⁺, for the glasses containing low valency cations, while they shift to higher energies with increasing ionic radius, in the order of Ti⁴⁺, Zr⁴⁺ and Th⁴⁺ or in the order of Nb⁵⁺ and Ta⁵⁺, for the glasses containing high valency cations.In glasses containing large amounts of PbO, strong bands due to PB²⁺ ions appear in the lower energy regions of 6.3–5.6 eV and 5.2–4.7 eV.     

Crystallization in fluoride glasses: I. Devitrification on reheating

The devitrification of glass from the BaF₂LaF₃ZrF₃AlF₃ quaternary system is studied as a function of sample size and heating rate by differential scanning calorimetry. Results are analyzed in terms of a theory of non-isothermal crystallization kinetics similar to that of Matusita and Sakka but modified to allow for diffusion controlled growth of the crystallites.     

Octahedral fluoride glasses: Raman spectra and structure of niobium pentafluoride

Raman spectroscopy is used to characterize the NbF₅ phases in the temperature range 80–500 K. A new clear glass is formed by quenching the melt to liquid nitrogen temperatures having a glass transition at ～206 K and crystallization at ～233 K. For all phases including the melt, the glass, the supercooled liquid, the crystalline solid and the gas, the Raman spectra show a rather common high frequency band at ～760 cm^?1 which is attributed to the Nb–F terminal frequency of partially bridged ‘NbF₆’ octahedra. Based on the systematics of the Raman spectra for all phases and the literature physicochemical data a model is proposed for the glass and the liquid phases where ‘NbF₆’ octahedral bridged in cis and/or trans configurations form a variety of cyclic and/or chain structures which intermix building up the overall structure. At exceptionally low energies (<11 cm^?1) a rather weak in intensity Boson peak is observed in the glass which shifts to even lower energies with increasing temperature. Librational and/or tortional motions of the bridged octahedra participating in the glass structure are possible candidates for the origin of this peak.     

Electron spin resonance studies of iron-group impurities in beryllium fluoride glasses

Electron spin resonance investigations have been carried out on unirradiated BeF₂ glasses. Two relatively intense resonances were observed in a water-free distilled glass known to contain 49 ppm Ni, 13 ppm Mn, and <20 ppm Fe. One of these was the paramagnetic resonance spectrum of Mn²⁺. Analysis of the observed ¹⁹F superhyperfine structure demonstrated this manganese to occupy distorted octahedral sites in the glass network. The second resonance was shown by temperature and frequency dependence studies, coupled with computer line shape analysis, to be a ferromagnetic resonance signal due to precipitated ferrite phases. The data suggest that these ferrites are somewhat heterogeneous and most likely comprize magnetite-like phases similar to NiFe₂O₄. An optical extinction curve rising into the ultraviolet with an approximate λ^?4 dependence is tentatively ascribed to light scattering by ferrite particles ～1000 Å in diameter.     

Morphology of swift heavy ion tracks in metallic glasses

Swift heavy ion irradiated metallic glasses were studied using synchrotron based small angle X-ray scattering (SAXS). Ribbons of Fe₈₀B₂₀, Fe₈₅ B₁₅, Fe₈₁B_13.5Si_3.5C₂ and Fe₄₀Ni₄₀B₂₀ were irradiated with 11.1 MeV/nucleon (MeV/u) ¹³²Xe, ¹⁵²Sm, ¹⁹⁷Au and 8.2 MeV/u ²³⁸U ions to fluences between 1 × 10¹⁰ and 1 × 10¹² ions/cm². The SAXS measurements provide evidence for the formation of ion tracks and allow a quantitative analysis of the track ensemble in all studied materials. The ion tracks have been well described by cylinders with abrupt boundaries and an electronic density change of (0.03 ± 0.01)% between track and matrix material. An inelastic thermal spike model was fitted to the experimental track radii to determine the critical energy density required to create an ion track. Despite the similar energy loss and track cross-sections, 30% higher track creation threshold is apparent for the binary alloys.     

Influence of chlorine-fluorine substitution on the electrical properties of some fluoride glasses

Study of electrical properties of two series of glasses (ZrF₄)₅₄(BaF₂)₃₀(ThF₄)₅(LaF₃)₃(RbF)_8(1−x)(RbCl)_8x (0 x 1) and (ZrF₄)₅₀(BaF₂)₃₀(ThF₄)₅(LaF₃)₃(RbF)_12(1−x)(RbCl)_12x (0 x 1) demonstrates the existence of a mixed mobile anion effect in these anion-conducting glasses. The effective medium approach has been applied to these materials: a satisfactory fitting is obtained as a function of the Cl/(Cl + F) ratio and temperature; the ionic transport in these glasses takes place along preferential pathways.     

New fluoride glasses based on 4f and 5f elements

New fluoride glasses have been isolated in the ternary systems ThF₄-LnF₃-BaF₂ with Ln = the lanthanides Yb, Y, Tm. The melt must be quenched to reduce crystallization. They are simply prepared from oxides by an appropriate NH₄F, HF treatment. The IR transmission is remarkable, the optical window lying in the 0.25-10 μm region.