Lithium Fluoroborate Glasses Research Articles

Structural, thermal, dielectric and ac conductivity properties of lithium fluoro-borate optical glasses

Transparent and stable glasses in the chemical composition of Li2O–LiF–B2O3–MO (M=Zn and Cd) have been prepared by a conventional melt quenching method. For these glasses, absorption spectra, structural (XRD, FT-IR, and Raman spectra), thermal (TG–DTA and DSC), dielectric (ɛ′, ɛ″, tanδ), ac conductivity (σac), and electric modulus (M′ and M″) have been investigated. Amorphous nature of these glasses has been confirmed from their XRD profiles. The LFB glasses with the presence of ZnO or CdO an extended UV-transmission ability has been achieved. The measured FT-IR and Raman spectra have exhibited the vibrational bands of B–O from [BO3] and [BO4] units and Li–O. The dielectric properties (tanδ, dielectric constant (ɛ′), dielectric loss (ɛ″)), electrical modulus and electrical conductivity (σac) of these glasses have also been studied from 100Hz to 1MHz at the room temperature. Based on the trends noticed in the ac conductivities, the present glasses could be found useful as battery cathode materials.

Role of the local structure and the energy trap centers in the quenching of luminescence of the Tb3+ ions in fluoroborate glasses: A high pressure study

The concentration and pressure dependent luminescence properties of the Tb(3+) ions in a lithium fluoroborate glasses have been studied by analyzing the deexcitation processes of the (5)D(4) level at ambient conditions as well as a function of pressure up to 35 GPa at room temperature. The luminescence spectra of Tb(3+) ions have been measured as a function of pressure and observed a continuous redshift as well as a progressive increase in the magnitude of the crystal-field splittings for the (5)D(4)-->(7)F(3,4,5) transitions. Monitoring the (5)D(4)-->(7)F(5) transition, the luminescence decay curves have been measured and analyzed in order to understand the dynamics of the deexcitation of the Tb(3+) ions in these glasses. At ambient conditions a nonexponential behavior has been found for doping concentrations as low as 0.1 mol % of Tb(4)O(7), although no cross-relaxation channels exist to explain this behavior. The modelization of the energy transfer processes surprisingly shows that the nonexponential character of the decay curves of the (5)D(4) level with concentration or with pressure has to be ascribed to energy transfer to traps without migration of energy between Tb(3+) ions. For all the experimental situations the nonexponential character of the decay curves is well described by the generalized Yokota-Tanimoto model with a dipole-dipole interaction between the Tb(3+) ions and the nearby luminescence quenching traps. The luminescence properties observed with releasing pressure are slightly different to those obtained while increasing pressure suggesting a local structural hysteresis in the lithium fluoroborate glass matrix giving rise to the generation of a new distribution of environments for the Tb(3+) ions.

Structural, optical and thermal studies of Eu 3+ ions in lithium fluoroborate glasses

Borate glasses doped with trivalent europium were prepared by the conventional melt quenching technique, in the chemical composition of (49.99- x)B 2O 3 + 25Li 2O + 25LiF+ xEu 2O 3 by varying the concentration of the rare earth ion in the order 0.01, 0.1, 1, 2 and 3 wt% and their structural, luminescence and thermal behavior have been reported. The XRD and FTIR spectra reveal the glass structure and the functional groups. The UV–VIS, luminescence spectra and lifetime of the Eu 3+ ions were measured. The local site symmetry around the Eu 3+ ions were evaluated through the luminescence intensity ratio (R) of the 5D 0 → 7F 2 to 5D 0 → 7F 1 transitions. Optical measurements have been carried out to explore the optical properties such as bonding parameters, Judd–Ofelt parameters, stimulated emission cross-section, transition probability, branching ratio, radiative lifetime, etc. The lifetime measurements of the 5D 0 level as a function of the concentration of Eu 3+ ion have been found and is comparable to other reported for Eu 3+ doped borate, phosphate glasses and higher than that for the tellurite glasses. The thermal properties such as glass transition, crystallization and melting temperatures of the Eu 3+ glasses were studied through the DSC traces in the temperature range of 30−1200 °C at a heating rate of 10 °C per minute. The change in optical properties with the variation of Eu 3+ ion concentration have been discussed and compared with similar results.

Structural, optical and thermal investigations on Dy3+ doped NaF–Li2O–B2O3 glasses

Abstract Structural, optical and thermal properties of Dy 3+ doped lithium fluoroborate glasses have been studied for various concentrations of Dy 3+ from 0.5 to 5 wt%. The XRD studies confirm the amorphous nature of the glasses while the FTIR spectra reveal the presence of BO 3 and BO 4 local structural units. The UV–VIS–NIR absorption studies were carried out to calculate the bonding parameters ( β ¯ and δ ), to identify the ionic/covalent nature of the glasses. The JO parameters, experimental and theoretical oscillator strengths were also determined and reported. The luminescence spectra have been studied to determine the radiative transition probability ( A ), stimulated emission cross section ( σ P E ) and the experimental and calculated branching ratios ( β R ) for the excited levels that include 4 F 9/2 → 6 H 11/2 , 6 H 13/2 , and 6 H 15/2 transitions. The variation of optical properties with varying concentrations of dysprosium oxide content in the glasses are reported and discussed. The thermal behavior of Dy 3+ doped lithium fluoroborate glasses have been reported by recording DSC thermograms.

Fluorescence line narrowing spectral studies of Eu 3+-doped lead borate glass

A lead borate glass of molar composition 49.5H 3BO 3–49.5PbO–1.0Eu 2O 3 was prepared and studied by broadband and fluorescence line narrowing spectral techniques. Site-selective 5D 0 → 7F 0,1 emission spectra were obtained under resonant excitation at different wavelengths along the 7F 0 → 5D 0 transition. These studies have been used to investigate the site-to-site variations in the spectroscopic properties of Eu 3+ ions in the lead borate glass at 13 K. The energies of the Stark levels of the 7F 1 multiplets are obtained from the experimental fluorescence line narrowing spectra and crystal-field analysis has been carried out, assuming C 2v orthorhombic symmetry, for each of the excitation energies. The distribution environments and the local structures of Eu 3+ ions in lead borate glass are found to be almost similar to calcium diborate glass and lies intermediate between Eu 3+-doped sodium borosilicate and lithium fluoroborate glasses.

Pressure-induced energy transfer processes betweenSm3+ions in lithium fluoroborate glasses

Fluorescence decay curves for the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{G}_{5/2}}}^{6}{H}_{7/2}$ transition of ${\mathrm{Sm}}^{3+}$ ions in lithium fluoroborate glasses for different lanthanide concentrations have been measured as a function of pressure up to 21 GPa at room temperature. At ambient conditions, for 0.2 mol % of ${\mathrm{Sm}}^{3+},$ a single exponential completely describes the fluorescence decay curve. On the contrary, in the case of 2 mol % of ${\mathrm{Sm}}^{3+},$ a distinct nonexponential behavior is observed, indicating that energy transfer processes only occur for higher concentrations in fluoroborate glasses. With increasing pressure the fluorescence decays show a more pronounced nonexponential behavior, even for the sample with low concentration, accompanied by a fast decrease of the lifetimes. Cross relaxation between ${\mathrm{Sm}}^{3+}$ ions can explain the energy transfer processes, for which migration does not play a relevant role. A generalized Yokota-Tanimoto model has been used to explain this behavior. For the first time, the lifetime and the energy transfer parameter have been obtained and analyzed independently as a function of pressure. Moreover, their contributions to the luminescence intensity also have been analyzed.

On the local structure of Eu3+ ions in oxyfluoride glasses. Comparison with fluoride and oxide glasses

Broadband and fluorescence line narrowing optical spectroscopic studies have been used to investigate the local environments of Eu3+ ions in lithium fluoroborate glasses. From the vibronic spectra, different borate groups coupled with the Eu3+ ions have been identified. A pulsed tunable dye laser has been used to selectively excite the D05 level of the Eu3+ ion and the subsequent D05→F17 fluorescence spectra have been monitored as a function of the exciting wavelength. From these FLN studies, three F17 Stark levels have been identified and a C2v orthorhombic symmetry has been assumed in the subsequent calculation of the crystal-field parameters for the different environments occupied by the Eu3+ ions in the glass. The second rank crystal-field parameters have been systematically analyzed for the Eu3+:lithium fluoroborate glass from the site dependent behavior of the F17 level splitting. The importance of the J-mixing in the crystal-field analysis has been emphasized. An appropriate method for comparing the crystal-field interactions in different glasses has been proposed by analyzing the F17 level. Thus, results obtained for the Eu3+:fluoroborate have been compared with recalculated results in other Eu3+ doped fluoride, borate, silicate, and borosilicate glasses. An intermediate behavior between Eu3+:oxide and Eu3+:fluoride glasses is observed for the local structure of the Eu3+ ions in the fluoroborate glass, indicating the active participation of fluorine ions in the immediate environments of the lanthanide ion in this glass.

Spectroscopy of Pr 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption and emission spectra of 1 mol% Pr 3+ doped lithium borate and lithium fluoroborate glasses have been recorded. The intensities of f–f transitions are parameterized in terms of Judd–Ofelt (JO) intensity parameters Ω λ ( λ=2, 4 and 6). The JO parameters obtained with modified JO theory have been used to predict radiative properties such as spontaneous emission probabilities ( A), lifetimes ( τ R) and branching ratios ( β R) for all the 12 excited states of these Pr 3+ doped glasses along with some of the reported Pr 3+ : systems. The predicted β R are compared with the experimental values for the emission from 3P 0 and 3P 1 levels. The stimulated emission cross-sections are also evaluated for all the observed emission transitions. The β R values for the potential laser transitions including the 1G 4→ 3H 5 (1.3 μm) transition useful for fibre amplifier have been compared for 17 Pr 3+ : systems. The effect of compositional changes of the glasses on the optical properties of Pr 3+ ions have been discussed.

High-pressure fluorescence study of Sm3+ : lithium fluoroborate glass

Fluorescence spectra of Sm3+ in 49.5 H3BO3+49.5 LiF+1.0 Sm2O3 glass (L5FBS) have been measured under pressure up to 9GPa at room temperature and also at 2K at ambient pressure. In this pressure range, a red-shift of the order of −5cm−1/GPa is noticed for 4G(4)5/2→6HJ(J=132,112,92,72and52) multiplet transitions. These shifts are explained by the increased interaction of Sm3+ with its surrounding ligands under pressure. The luminescence decay curves of 4G(4)5/2 were studied up to 21GPa and were found to be non-exponential for all pressures studied. This result can be explained either by the existence of two different Sm3+ sites with a slow and a fast fluorescence decay component or by energy transfer processes. The decay time exhibits a strong decrease with increasing pressure. At 21GPa the decay time decreases by a factor of two with respect to the ambient pressure value. The radiative properties (lifetime, branching ratios, etc.) calculated by the Judd–Ofelt theory at ambient conditions are in close agreement with the experimental values.

Optical properties of Sm 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption, excitation, emission spectra and lifetimes are presented for Sm 3+ ions in lithium borate and lithium fluoroborate glasses. Compositional dependence of Judd–Ofelt parameters has been evaluated and these parameters are used to predict radiative lifetimes ( τ R) and branching ratios ( β R) for some excited 4G(4) 7/2, 4G(4) 5/2, 6F 11/2, 6F 9/2, 6F 1/2, 6H 13/2, 6H 11/2 and 6H 9/2 levels. The radiative properties have also been predicted for these excited levels of Sm 3+:borate, oxide, phosphate, fluoride and fluorophosphate glasses and Sm 3+:Y 3Al 5O 12 crystal. The values of electric ( A ed) and magnetic ( A md) dipole transition probabilities, τ R and β Rare presented for the above excited levels. The Judd–Ofelt intensity parameters have been used to predict oscillator strengths which are found to be useful to assign the closely spaced multiplets. The predicted values of τ R and β R are compared with the experimental values for 4G(4) 5/2 level to its lower levels. The stimulated emission cross-sections, σ( λ p), were also evaluated for 4G(4) 5/2→ 6H J transitions. The dependence of the optical properties due to compositional changes of the glasses are discussed and compared with similar results.

Optical spectroscopy of Eu 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption, excitation and emission spectra of Eu 3+ ions in lithium borate and lithium fluoroborate glasses have been investigated. Judd–Ofelt intensity parameters are derived from the integrated absorption spectra and also from the emission spectra under various constraints. The relative merits of thermal correction to the oscillator strengths of the transitions originating from the ground state ( 7 F 0 ) of Eu 3+ ion observed in the absorption spectra have been discussed. The Judd–Ofelt parameters obtained from the emission spectra have been used to calculate the total spontaneous emission probabilities ( A), lifetimes ( τ R) and branching ratios ( β R) for eight excited levels that include, 5 K 6, 3 P 0 , 5 H 3 , 5 L 7 , 5 D 3 , 5 D 2 , 5 D 1 and 5 D 0 . The predicted values of τ R and β R are compared with the measured values for 5 D 0 level. The stimulated emission cross-sections ( σ ( λ p)) are also evaluated for the 5 D 0→ 7 F J and 5 D 1→ 7 F J transitions. The variation of optical properties with compositional changes of lithium oxide and lithium fluoride contents in the glasses are discussed and compared with similar results.

ESR and optical absorption spectra of Ni(II) ions in lithium fluoroborate glasses

The results of the investigation of the structure of Ni(II) ions in x LiF-(100−x) B2O3 glasses with 5⩽x⩽30 mol% using ESR and optical absorption techniques are reported. Electron spin resonance spectra of Ni(II) ions doped glasses exhibit a symmetric line shape centred at g=2.36±0.01 at room temperature. Remarkable changes have been observed in the intensity and line shape with changes in concentration of LiF and when the spectra were recorded in the temperature range 123–453 K. The optical absorption spectra were recorded at room temperature. The observed bands have been interpreted in terms of ligand field theory. From the spectral analysis, the crystal field parameter, Dq, and the Racah interelectronic repulsion parameters, B and C, have been evaluated. By correlating the ESR and optical absorption data, the covalency parameter has been evaluated.

EPR and optical absorption spectra of some paramagnetic ions in lithium fluoroborate glasses

The results of an electron paramagnetic resonance and optical absorption study of lithium fluoroborate glasses separately doped with Ti3+, Mn2+, Co2+, Ni2+, Cu2+ and Gd3+ ions are presented. The results are all consistent with optical absorption measurements and show that the ions are generally in sites with octahedral coordination except for Gd3+, which dictates its own environment and occupies sites surrounded by polyhedra of more or less irregularly distributed ligands with high coordination number (≥ 6).

Analysis of electric relaxation in sodium trisilicate and lithium fluoroborate glasses from 10 2 to 10 9 Hz and 25 to 300°C

It was found that subtraction of effects of an assumed ‘Warburg’ surface impedance, z = z 1(i gw − a , from measured parallel capacitance and conductance yields constants low frequency values with relaxation of both at higher frequencies. After subtraction of dc conductance, the remaining complex, ϵ ∗ , is described quite well by the Cole-Davidson (CD) relaxation function with β ∼ 0.36 plus excess absorption at the highest frequencies. The high frequency conductivity approaches the linear variation with ω proposed by Wong and Angell. It can also be joined smoothly to extrapolated far IR reflectivity measurements of damped cation motion resonances (unpublished results of Burns and Risen). The following unified interpretation is proposed: cation vibrations in local potential minima are precursors of occasional escapes to adjacent sites and ensuing diffusive charge displacements and transport which is ultimately blocked by space charge accumulations near electrodes.

Dielectric and infrared reflectance studies of inorganic oxide glasses

The dielectric properties of several types of ionic oxide glasses, sodium trisilicate and a series of lithium fluoroborate glasses, have been measured in the infrared and far infrared by reflectance methods and analyzed together with those reported earlier which were obtained in the 1 × 10 2 to 2 × 10 9 Hz region at temperatures from 25 to 300 °C by bridge and time domain reflectance (TDR) techniques, Together, these provide nearly continuous data from low frequency through 1.35 × 10 4 Hz, with a gap from about 2 × 10 9 to 7.5 × 10 11 Hz. Interpolation through this range has been addressed by consideration of the behavior of ϵ′(ω) at the limits of the measured ranges. It has been found that the damped harmonic oscillator-modelled ϵ″ (ω) features in the infrared and far infrared lead to ϵ′(ω) curves which extrapolate to those ϵ′(ω) curves measured at lower frequency and provide the interpolation and effectively continuous spectra from low frequency through the infrared.

Behavior of halide ions in borate glass

Infrared absorption, laser Raman scattering as well as X-ray induced ESR spectra have been measured for lithium fluoroborate and chloroborate glasses. For the glasses with an identical Li 2 O/B 2 O 3 ratio, the chloroborate glasses showed vibrational spectra similar to those observed in the halide free borate glasses, while the fluoroborate glasses showed different ones. ESR spectra confirmed that Cl 2 - radical is formed in the chloroborate glasses upon the X-ray irradiation, but F 2 - radical has not been detected for the fluoroborate glasses even at 77 K. It is concluded that F is covalently bonded to B, but Cl is just present in interstitial sites in the borate glass as a free ion.

Far IR spectra and electrical conductivity of Li and Na glasses by laboratory and computer simulation experiments

Admittance bridge measurements in the frequency range 0.1–106 Hz have been combined with Fourier transform interferometric spectral measurements in the range 1012−1013 to yield major portions of the complete a.c. field response function for some highly conducting lithium fluoroborate and sulfoborate glasses. Interpretation of these results has been assisted by studies of the detailed dynamics of ion motion revealed by ion dynamics computer simulation studies of high fictive temperature lithium and sodium silicate glasses, and of some unphysical glasses with (a) massive, slowly vibrating “oxygen ions”, and (b) light Na+ ions of the same mass as the Li ions.