Diborate Units Research Articles

Enhanced near-infrared luminescence at 1.07 μm of Nd3+ doped PbCl2–Li2B4O7 glasses for solid state laser and optical fiber amplifier applications

Abstract Nd3+ doped PbCl2–Li2B4O7 glasses have been synthesized using melt quenching technique. XRD spectra reveals the signature of non-crystalline behavior of synthesized glasses. DSC studies reveal glass transition temperature and thermal stability parameter (ΔT) exhibit composition dependent trends and ΔT is as high as 114 °C. UV–Vis spectra contain eleven well-defined absorption peaks with five intense absorption bands centered at 527, 586, 750, 806 and 876 nm which are assigned to transitions from 4I9/2 → 4G7/2, [4G5/2,2G7/2], [4F7/2, 4S3/2], [4F5/2, 2H9/2] and 4F3/2 respectively. The maximum absorption cross section 1 . 139 × 10 − 20 cm2 of 806 nm pump level transition 4I9/2 → [4F5/2, 2H9/2] is comparable with maximum absorption cross section 1 . 149 × 10 − 20 cm2 of 586 nm hypersensitive transition 4I9/2 → [4G5/2, 2G7/2]. Near infrared emission spectra exhibit very high emission intensity at 1070 nm for 4F3/2 → 4I11/2 transition along with two dominant emission bands at 904 and 1340 nm corresponding to 4F3/2 → 4I9/2 and 4F3/2 → 4I13/2 transitions. This high absorption and emission intensities are attributed to high degree of covalent environment of ligands surrounding Nd3+ ions. Bonding parameter, δ increase with Nd2O3 content which suggests dominance of covalency between Nd3+ ion and ligands. 11B MAS NMR studies reveal that, the addition of Nd2O3 to Li2B4O7 converts diborate units into chain-like network structures such as charged trigonal borate units which is further supported by FTIR study. Two photon absorption coefficient shows linear relationship with optical band gap energy. Hence Nd3+ doped PbCl2–Li2B4O7 glasses with superior absorption and emission properties are found to be potential candidates for near-infrared solid state laser and optical fiber amplifier applications.

Optical Properties and Structural Studies on Nd<sup>3+ </sup>Doped Borate Glasses Containing Heavy Metal Oxide

Abstract. Neodymium doped sodium bismuth borate (Na2O-Bi2O3-B2O3) glasses were prepared by melt quenching method. Amorphous nature of the glass is confirmed through the X-ray diffraction study. Density of the investigated glasses increases systematically with Bi2O3 concentration. Glass transition temperature decrease slightly with increase of Bi2O3 content and could be due to increase in the number of weaker Bi-O linkages by stronger Nd-O linkages. Fourier Transform - Infrared (FTIR) spectroscopy has been carried out. The IR spectra of the glasses reveal that the strong network consisting of diborate units and is unaffected by the variation of Nd3+ concentration. UV-Visible absorption studies have been performed on these glasses to examine the optical spectra and the optical band gap energy has been calculated. The intensity of the absorption band increases with the increase of Nd3+ concentration. This is due to the formation of non-bridging oxygens (NBO’s) in the structure.

The role of lead oxide on structural and physical properties of lithium diborate glasses

Pseudo-binary (100−x)Li2B4O7–xPb3O4, with x=0–70mol% PbO have been prepared and their properties investigated. The glass transition temperature, density and molar volume have been determined as a function of composition. The values of Tg and the molar volume decrease non-linearly while the density increases as the Pb3O4 content is raised. Infrared spectra of the glasses reveal that a strong network consisting of diborate units breaks up by the addition of Pb3O4. The absorption bands below 620cm−1 show that PbO is one of the network formers of the glasses 70⩾Pb3O4⩾10; as they can be associated with vibrations of (PbO4)2− grouping. PbO plays a dual role in the glass network. The calculated values of N4 [the fraction of borons which are tetrahedral] slightly decrease with PbO content up to 30mol% and then increase with Pb3O4 content up to 50mol%, then followed by a decrease as the Pb3O4 content rises further. The Vickers hardness of the glasses varies as a function of the PbO content in the same manner as the variation of N4. The dc conductivity decreases with the Pb3O4 concentration up to about 30mol% and then increases thereafter.

Spectroscopic investigations and physical properties of Mn 2+ doped mixed alkali zinc borate glasses

Spectroscopic investigations on Mn 2+ doped 20ZnO + xLi 2O + (30− x)Na 2O + 50B 2O 3 (5 ≤ x ≤ 25) (ZLNB) glasses reveal the non-linear behavior in their physical and structural properties. FT-IR spectra of ZLNB glasses reveal diborate units in the borate network. EPR spectra exhibit characteristic resonance signals of Mn 2+ ions. A well resolved six line hyperfine structure around g = 2.02 corresponds to the sites of Type II, and a weak broad shoulder around g = 2.7 followed by an unresolved intense signal at g = 4.25 corresponding to sites of Type I are observed for their respective transitions. A large value of zero-field splitting parameter ( D) is observed and it behaves non-linearly, reaches a maximum at x = 15 mol% with increase in Li 2O content. Δ g values reveal the ionic nature of glass systems. Optical absorption spectra suggest the distorted octahedral site symmetry of Mn 2+ ions in the host. Mixed alkali effect is evident in bandgap and Urbach energies.

Correlation between physical and structural properties of Co2+ doped mixed alkali zinc borate glasses

The physical and structural properties of Co2+ doped 20ZnO+xLi2O+(30−x)Na2O+50B2O3 (5≤×≤25) (ZLNB) glasses have been studied and correlated. The physical and structural parameters of all the glasses are evaluated and a non-linear behavior is observed. No sharp peaks are observed in XRD patterns of the glass samples which confirm the amorphous nature. FT-IR spectra of ZLNB glasses reveal diborate units in borate network. The optical absorption spectra suggest the site symmetry of Co2+ in the glasses is near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibit the mixed alkali effect. All the samples are found to be strong and stable in structure with low values of Urbach energy which lie between 0.027eV and 0.039eV. The correlation between densities and Urbach energies of Co2+ doped ZLNB glasses with respect to Li2O content suggest a changeover conduction mechanism from electronic to ionic, with a diffusivity crossover point at x=15mol%.

Structural studies of some phospho-borate glasses using ultrasonic pulse–echo technique, DSC and IR spectroscopy

Glasses in the system (95− x ) [0.25 Na 2 O–0.75 B 2 O 3 ]– x P 2 O 5 –5 Fe 2 O 3 (0⩽ x ⩽15 mol%), have been prepared by the melt quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of P 2 O 5 on the structure of the glass system. Elastic properties Poisson's ratio, micro-hardness and Debye temperature have been investigated using sound wave velocity measurements at 4 MHz (both longitudinal and shear) at room temperature. The results showed that the density and the molar volume increase as both sound velocities and the determined glass transition temperatures decrease with increasing the contents of P 2 O 5 . Infrared spectra of the glasses reveal that the borate network consists of diborate units and is affected by the increase in the concentration of P 2 O 5 content as a second network former. These results are interpreted in terms of the replacement of the diborate units with B–O–B bridges by phosphate units with non-bridging oxygens (NBOs). Therefore, the elastic moduli are observed to decrease with the increase in P 2 O 5 content.

The investigation of the influence of lead oxide on the formation and on the structure of lithium diborate glasses

Pseudo-binary (100 − x) Li 2B 4O 7· xPbO, where x = 0, 5, 15, 25, 35, 45, 55 and 65 mol%. PbO have been investigated. The glass transition temperatures, density and molar volume have been determined. Both T g's values and molar volume decreased non-linearly while the density increased by increase the PbO content. Infrared spectra of the glasses reveal that the strong network consisting of diborate units is break open by PbO. The absorption bands below 620 cm −1 show that PbO is one of the network former of glasses 65 ≥ PbO ≥ 5 which can be associated with vibrations due to [PbO 4] 2− type of grouping are become sharp and high intensities by increase PbO content. PbO plays the dual role in the glass network. The calculated values of N 4 slightly decreased by increase PbO content up to 25 mol% and then increased up to 45 mol% PbO, then decreases above it. Proving that three-coordinated boron atoms are predominant in these glass samples. The Vicker's hardness values of the glasses vary as a function of the PbO content in a manner that N 4 varied. The dc conductivity decreased by increase PbO concentration up to about 25 mol% and then increased by increase the concentration of lead oxide.

Physical and structural properties of some bismuth borate glasses

Glasses in the system ( x/2)Bi 2O 3–( x/2)Nb 2O 5–(1 − x)Na 2B 4O 7, 0 ≤ x ≤ 0.3, have been prepared by the melt quenching technique. Elastic properties and Debye temperature ( θ D) have been investigated using sound velocity measurements at 4 MHz. The ultrasonic parameters along with the IR spectroscopic studies have been employed to study the role of Bi 2O 3, and Nb 2O 5 on the structure of Na 2B 4O 7 glass. The density, the molar volume, the sound velocities, and the glass transition temperatures of these samples have been found to be compositional dependent. The results indicate that Bi 2O 3, and Nb 2O 5 act as a network modifier in the range 0 ≤ x ≤ 0.15, while beyond x = 0.15, Nb 2O 5 acts as a network former which affects the diborate units that mainly consist the strong borate network. These results are interpreted in terms of the transformation of NbO 6 into NbO 4, the increase in the number of non-bridging oxygen atoms, and the substitution of longer bond lengths of Bi–O, and Nb–O in place of shorter B–O bond. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of Bi 2O 3, and Nb 2O 5 on the Boron-coordination number of the glass structure and to the relatively large electron–phonon anharmonic interactions.

Elastic properties and structural studies on some zinc-borate glasses derived from ultrasonic, FT-IR and X-ray techniques

Glasses in the system (1 − x) [29Na 2O− 4Al 2O 3− 67B 2O 3]− xZnO (0 ≤ x ≤ 35 mol%), have been prepared by the melt quenching technique. Elastic properties, X-ray and FT-IR spectroscopic studies have been employed to study the role of ZnO on the structure of the investigated glass system. Elastic properties and Debye temperature have been investigated using sound wave velocity measurements at 4 MHz at room temperature. The results showed that the density increases and the molar volume decreases while both sound velocities and the determined glass transition temperatures decrease with increase in x. X-ray and infrared spectra of the glasses reveal that the borate network consists of diborate units and is affected by the increase in the concentration of ZnO content. These results are interpreted in terms of the decrease in the N 4 values (fraction of tetrahedral coordinated boron atoms), and substitution of longer bond lengths of Zn–O in place of shorter B–O bond. The results indicate that Zinc ions have been substituted for boron ions as tetrahedral network former ions. The elastic moduli are observed to increase with the increase of ZnO content.

Structural and acoustical studies of lead sodium borate glasses

Abstract Glasses in the system Na2−2xB4−4xPbxO7−6x, 0 ≤ x ≤ 0.8, have been prepared by the melt quenching technique. Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The ultrasonic parameters along with the IR spectroscopic studies have been employed to study the role of PbO on the structure of Na2B4O7 glass. The density, the molar volume, and the ultrasonic parameters of these samples have been found to be compositional dependent. The results indicate that PbO acts as a network modifier in the range 0 ≤ x ≤ 0.4, while beyound x = 0.4, PbO acts as a network former which affects the diborate units that mainly consist the strong borate network. These results are interpreted in terms of the IR analysis that indicates the transformation of the structural units BO3 into BO4, the increase in the number of non-bridging oxygen atoms, and the substitution of longer Pb O bond length, in place of shorter B O bond. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of PbO on the boron-coordination number of the glass structure and to the relatively large electron–phonon anharmonic interactions. A good correlation was observed between the experimentally determined elastic moduli and those computed according to Makishima–Mackenzie model.

Synthesis and several features of the Na2O-B2O3-Bi2O3-MoO3 glasses

Glasses in the system Na2−2xB4−4xBixMo0.5xO7−4x, 0 ≤ x ≤ 0.4, have been prepared by the melt quenching technique. Elastic properties and IR spectroscopic studies have been employed to study the role of Bi2O3 and MoO3 on the structure of Na2B4O7 glass. Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The results showed that the density and the molar volume increase while both sound velocities and the determined glass transition temperatures decrease with increase in x. Infrared spectra of the glasses reveal that the strong borate network consists of diborate units and is affected by the increase in the concentration of Bi2O3, and MoO3. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of longer bond lengths of Bi–O, and Mo–O in place of shorter B–O bond and the change in Na+ ion concentration. The results indicate that bismuth and molybdenum ions have been substituted for boron ions as network modifier ions. The elastic moduli are observed to increase with the increase in Bi2O3 and MoO3 content. This contradiction in the elastic moduli–molar volume relation is attributed to the role of the respective bonds.

Structural investigations of sodium diborate glasses containing PbO, Bi2O3 and TeO2: Elastic property measurements and spectroscopic studies

Pseudo-binary sodium borate glasses containing (1−y)Na2B4O7–yMaOb (where MaOb=PbO, Bi2O3 and TeO2) (y=0.25, 0.5, 0.67 and 0.79) have been investigated. Sound velocities (longitudinal and shear) have been measured at 10MHz frequency using quartz transducers. Density increases with increase of y and the molar volume decreases. Sound velocities also decrease with increasing y till y≈0.66 above which it increases slightly. Steeper decrease in velocities has been observed in TeO2 containing glasses. Elastic moduli, Poisson’s ratio and Debye temperature have been calculated. Glass transition temperatures have also been determined and it decreases with increase of y. Tg also exhibits a dependence on the cationic charge in MaOb. Infrared spectra of the glasses reveal that the strong network consisting of diborate units is affected only by PbO and only very marginally by Bi2O3 and TeO2. Only glasses with high concentrations of Bi2O3 and TeO2 reveal the presence of mixed bridges such as Bi–O–B and Te–O–B. Consistent with the IR spectral observations, the N4 values of 11B MAS-NMR remain close to the ideal value of 0.5 of the diborate composition in most of the glasses. A structural model based on the observation that the diborate network is unaffected by Bi2O3 and TeO2 where as PbO opens up and breaks the diborate units is shown to be consistent with all of the experimental observations including mechanical properties.

Analysis of the structure of lead borosilicate glasses using laser ionization time of flight mass spectroscopy

We report on high resolution laser ionization time-of-flight mass spectroscopy (LITOF-MS) measurements of lead borosilicate and sodium-doped lead borosilicate glasses. This technique permits the observation of intermediate range mesounits, and provides new insights into the glass network structure. In lead borosilicates we observed strong mixing of borate and silicate groupings, a likely absence of diborate units, and the formation of boroxol rings with one lead cation (PbB 3O 6) at borate-rich compositions. The spectra also suggest the growth of a limited lead oxide subnetwork at high Pb contents. In the sodium-doped glasses we see a preference of the sodium for boron units, and the simultaneous appearance of sodium-containing silicate units between 10 and 24 mol% Na 2O, though borate association remains predominant. The reedmergnerite unit (BSi 4O 10) is seen in very small amounts in both glass families.

Determination of the mesostructure of lead borate glasses using laser photoionization mass spectroscopy

We have investigated the structure of lead borate glasses up to high lead contents using a high-resolution reflectron time-of-flight mass spectrometer. The glasses showed the repeatable presence of intermediate-range units, which varied in relative abundance depending on composition. This direct measurement of the network showed a high abundance of (B3O5) and (PbB3O6) groups, which are likely to arise from metaborate rings, as well as the rise of ortho- and pyroborate units. Smaller quantities of entire diborate units (B4O9, with added lead and boron atoms for charge compensation) were also observed.

The structure of Ag- and Li-borate glasses of the composition (Ag 2O·2B 2O 3) 1- x(AgI) x and (Li 2O·2B 2O 3)

In both Li- and Ag-diborate glasses, the interpenetrating systems of diborate chains characteristics of the crystalline structure are completely destroyed. The Li-diborate glass is a disordered mixture of all possible borate-like configurations characterized by an ordering distance of about 4.5 Å for trigonal and of about 4 Å for tetrahedral borate units. In the Ag-diborate glass, the main features of the neutron scattering diagram can be simulated for small amounts of AgI ( x = 0.1) by an ordering of diborate units (cages) at a separation of 6.7 Å. For a greater amount of AgI ( x = 0.6), an appropriate number of diborate units have a separation of about 8.8 Å and the AgI phase forms clusters with a maximum diameter of about 8 Å.

Raman study of lead borate glasses

Glasses in the system xPbO: (100 − x)B 2O 3 (22 ≦ x ≦ 85 mol%) have been studied by Raman spectroscopy with a view to understand the effect of PbO on the borate network. The conversion of three-fold to four-fold coordinated boron takes place primarily by incorporation of BO 4 into boroxol rings in the form of pentaborate and diborate units. For high lead content back conversion of four to three coordination of borons occurs and the network consists primarily of pyroborate, orthoborate and metaborate groups.

11 B NMR spectra and structure of boric oxide and alkali borate glasses

High-resolution 11 B magic-angle-spinning (MAS) NMR investigations of boric oxide and alkali borate glasses have been carried out. The chemical shift of the trigonal boron shows anomalous behaviour around 10 mol. % alkali oxide. In an attempt to explain this unusual feature, we have carefully examined the structural model for B 2 O 3 glass. The study suggests that around 66% of the boron atoms is likely to be present in the boroxol units, the rest being present in loose BO 3/2 units. This model is not only consistent with the earlier literature but also shows that stringent topochemical factors are involved in the formation of the tetraborate and the diborate units in alkali borate glasses. It seems plausible that the remarkable tendency of B 2 O 3 to vitrify may itself have a structural origin.

IR investigation of amorphous BaO-Fe 2O 3-B 2O 3 glasses prepared using 1 mol% TiO 2

An infrared (IR) investigation of 35BaO-25Fe 2O 3-40B 2O 3glasses prepared by rapidly quenching the melts containing 1 mol% of TiO 2 at room temperature (25°C) is reported. The system is composed of BO 3 and BO 4 groups in the form of boroxol ring with tetraborate and diborate units forming the network structure. The iron oxide (Fe 3+) possesses the positions in the network to occupying tetrahedral coordination sites. The TiO 2 (Ti 4+) added by 1 mol% in the system probably maintain a tetrahedral (TiO 4) structure in the quenched glass, and thus induces growth of FeO 4 and BO 4 structural groups in the network. The network with latter groupings enhances the thermal stability as long as the sample does not crystallise significantly by given thermal treatments at temperatures upto 1000°C. A correlation with IR data has been made to account for the factors inhibiting the crystallisation of a system on addition of TiO 2.

B 11 nuclear magnetic resonance studies of Li 2OB 2O 3 glasses of high Li 2O content

A B 11 NMR study has been made of lithium borate glasses spanning the composition region from 37.5–65 mol% Li 2O. Values were obtained as a function of R = mol% Li 2O/mol% B 2O 3 for the fraction of boron in BO 4 units ( N 4), the fraction of symmetric BO 3 units ( N 3S) which have either zero or three non-bridging oxygens (NBO's), and the fractions of BO 3 units with one ( N 3A1) NBO's. A structural model is presented for the region 1 ⩽ R ⩽ 2.13 which involves the destruction of metaborate and loose BO 4 units as Li 2O is added. This extends an earlier model for the region 0.5 ⩽ R ⩽ 1 involving the destruction of diborate units to form metaborate and loose BO 4 units. The data are in generally good agreement with model predictions in the entire range (0 ⩽ R ⩽ 1.86) for which glasses can be made.