Effect of mixed transition-metal ions in glasses. Part III: The P2O5–V2O5–MnO system

Electrical and optical properties of phosphate glasses containing vanadium and manganese ions in the xP₂O₅–[(100 − x)(V₂O₅ + MnO)] (PVM) system have been investigated. This is the last article of a III-part series devoted to the electronic properties of phosphate glasses containing a mixture of transition ions. The first article was devoted to the electrical conductivity of glasses having the general composition: xP₂O₅–[(100 − x)(V₂O₅ + Fe₂O₃)] (PVF). Competitive transport of small polarons on V and Fe ion sites was found to contribute to a mixed transition-ion effect (MTE) in PVF glasses. Several features of MTE were found to be similar to the well known mixed alkali effect, observed in glasses containing two alkali ions. In the second article, optical absorption and electronic conduction of xP₂O₅–[(100 − x)(Fe₂O₃ + MnO)] (PFM) glasses were reported. In the absence of competitive transport between the two transition ions (since Mn ions were determined not to contribute to dc conduction), MTE was not observed. The most important feature of PFM glasses was a sharp increase in resistivity at a critical concentration of iron ions, similar to ‘metal–insulator transition’ (MIT). In the present article, we report a resistivity transition in PVM glasses which is similar to that exhibited by the glasses of the PFM series. While Fe ions contributed the carriers in the PFM glasses, V ions serve the same purpose in the PVM compositions. As the concentration of vanadium ions, n_V, is decreased in the composition range 0.82 > n_V > 0.40, resistivity (ρ) increases marginally. For glasses with 0.2 < n_V < 0.40, resistivity and the activation energy for dc conduction (W) increase sharply with decreasing n_V, marking the incidence of an MIT-type transition. As in the PFM glasses, the observation of MIT coincides with the transformation of small polarons to small bipolarons, which is confirmed by the shifting of the small polaron optical absorption band to higher energies with decreasing V concentration.     

Effect of OH− content on emission properties in Er3+-doped tellurite glasses

A series of tellurite glasses of composition, 75TeO₂–20ZnO–(5 ? x)La₂O₃–xEr₂O₃ (x = 0.05, 0.1, 0.3, 0.6, 1.0, 2.0, and 3.0 mol%) with different hydroxl content were prepared. The effect of Er³⁺ and OH^? groups concentration on the emission properties of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses was investigated. The constant K_OH–Er for Er³⁺ in tellurite glasses, which represents the strength of interaction between Er³⁺ and OH^? groups in the case of energy migration, was about 14 × 10^?19 cm⁴ s^?1. The interaction parameter C_Er,Er for the migration rate of Er³⁺: ⁴I_13/2 → ⁴I_13/2 transition in tellurite glass was 46 × 10^?40 cm², which indicates that concentration quenching in Er³⁺-doped modified tellurite glass for a given Er³⁺ concentration is much stronger than in silicate and phosphate glasses.     

Electronic transport properties of mixed transition metal ions doped borophosphate glasses

A series of borophosphate glasses in the composition (B₂O₃)_0.10–(P₂O₅)_0.40–(CuO)_0.50?x–(MoO₃)_x; 0.05 ? x ? 0.50 have been investigated for room temperature density and dc conductivity over the temperature range from 350 to 650 K. The density decreased with increase in MoO₃ over the composition range studied except a slight increase around 0.35 mole fraction. The observed initial decrease in conductivity with the addition of MoO₃ has been attributed to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity in the composition range 0.20 – 0.50 mol% of MoO₃ is ascribed to the mixed transition metal ion effect (MTE). Mott’s small polaron hopping model has been used to analyze the high temperature conductivity data and the activation energy for conduction has been determined. The low temperature conductivity has been analyzed in view of Mott’s and Greaves variable range hopping models. It is for the first time that conduction mechanisms have been explored and MTE detected in mixed transition metal ions doped borophosphate glasses.     

Structural and magnetic investigations of Fe2O3–TeO2 glasses

A series of tellurite glasses containing Fe₂O₃ with the nominal composition x(Fe₂O₃)–(1−x)(TeO₂), where x = 0.05, 0.10, 0.15, and 0.20, have been synthesized and investigated using X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Te 3d core level spectra for all glass samples show symmetrical peaks at essentially the same binding energies as measured for TeO₂ indicating that the chemical environment of the Te atoms in these glasses does not vary significantly with the addition of Fe₂O₃. Furthermore, the full-width at half-maximum (FWHM) of each peak does not vary with increasing Fe₂O₃ content which suggests that the Te ions exist in a single configuration, namely TeO₄ trigonal bipyramid (tbp). The O 1s spectra are narrow and symmetric for all compositions such that oxygen atoms in the Te–O–Te, Fe–O–Fe and Te–O–Fe configurations must have similar binding energies. The analysis of the Fe 3p spectra indicates the presence of Fe³⁺ ions only, which is consistent with the valence state of the Fe ions determined from magnetic susceptibility measurements.     

Optical and thermoluminescence properties of R2O–RF–B2O3 glass systems doped with MnO

Alkali fluoroborate glass systems containing manganese cations have been thoroughly investigated in order to obtain information about the structural role of manganese in such glass hosts. The amorphous phase of the prepared glass samples R₂O–RF–B₂O₃:MnO (with R = Li and Na) was confirmed from their X-ray diffraction. From the infrared spectra of these glass systems it was concluded that the glass structure contains two group of bands; one due to trigonal BO₃ units and the second due to the tetrahedral BO₄ units. As manganese was introduced, replacing lithium or sodium, it acts as a network modifier and the intensity of the second group of bands increases at the expense of the first group of bands. The optical absorption spectra of R₂O–RF–B₂O₃:MnO exhibited two conventional absorption bands; one due to Mn²⁺ ions and the other due to Mn³⁺ ions. The ESR spectra of these glasses showed a six-line hyper-fine structure centered at g = 2.01 (due to Mn²⁺ ions) and another signal at g = 4.3 (due to Mn³⁺ ions). The intensity of optical absorption bands and the ESR signal due to Mn²⁺ ions decreases with increasing MnO concentration indicating the conversion of Mn²⁺ ions into Mn³⁺ ions in the glass network. The thermoluminescence studies on these glass systems showed a quenching of TL output with increase in the concentration of MnO. All the obtained results were discussed on the basis of the glass structure and the conversion of Mn²⁺ into Mn³⁺ ions with increasing concentration of MnO in the glass systems.     

Characterization of B2O3 and/or WO3 containing tellurite glasses

Characterization of B₂O₃ and/or WO₃ containing tellurite glasses was realized in the 0.80TeO₂–(0.20 ? x)WO₃ ? xB₂O₃ system (0 ≤ x ≤ 0.20 in molar ratio) by using differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry techniques. Glasses were prepared with a conventional melt-quenching technique at 750 °C. To recognize the thermal behavior of the glasses, glass transition and crystallization temperatures, glass stability value, glass transition activation energy, fragility parameter were calculated from the thermal analyses. Density, molar volume, oxygen molar volume and oxygen packing density values were determined to investigate the physical properties of glasses. Fourier transform infrared spectra were interpreted in terms of the structural transformations on the glass network, according to the changing B₂O₃ and/or WO₃ content. Crystallization behavior of the glasses was investigated by in situ X-ray diffraction measurements and microstructural characterization was realized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.     

Influence of valence and coordination of manganese ions on spectral and dielectric features of Na2SO4–B2O3–P2O5 glasses

Sodiumsulpho borophosphate glasses with composition (40 ? x)Na₂SO₄–30B₂O₃–30P₂O₅: xMnO with x ranging from 0 to 5.0 mol% were manufactures. Dielectric spectra have been studied over a wide frequency range of 10²–10⁵ Hz and in the temperature range within 30–250 °C. The valance states of manganese ions and their ligand coordination in the glass network have been investigated using optical absorption, luminescence and ESR spectroscopy. The analysis of the these results has indicated that the manganese ions exist both in Mn²⁺ as well as in Mn³⁺ states and occupy prevailingly octahedral positions and serve as modifiers similarly to Na⁺ ions The values of dielectric parameters (dielectric constant, ε′(ω), loss tan δ and ac conductivity, σ_ac) were found to increase with increasing MnO content. They play a role of modifiers similarly to Na⁺ ions, create bonding defects and free ions viz., [SO₄]^2?, [POO_1/2O₂]^2?, [POO_0/2O₃]^3–, Na⁺ and (NaSO₄)^?. The migration of these charge carriers would build up space charge polarization and may be responsible for the enhanced dielectric parameters. The ac conductivity also is enhanced with increasing MnO content. The mechanism responsible for such increase is well explained based on the modifying action of Mn²⁺ ions.     

Influence of manganese ions on spectroscopic and dielectric properties of LiF-SrO-B2O3 glasses

Transparent glasses, obtained through melt quenching technique, with composition 30LiF-10SrO-(60-x)B₂O₃-xMnO, with 0 ≤ x ≤ 3 mol% (x = 0, 1, 1.5, 2, 2.5 and 3), were characterized by X-ray diffraction (XRD) and then they were analyzed for physical, spectroscopic studies (optical absorption, electron spin resonance (ESR) and FTIR) and dielectric properties (dielectric constant ε′, loss tanδ ?and conductivity σ_ac etc.). The results were analyzed and correlated with each other in the light of local environment and oxidation states of manganese ion in the glass network. The increase in the area of optical absorption peak and ESR signal intensity indicate that both Mn²⁺ and Mn³⁺ ions exist in octahedral symmetry are increased with increasing MnO dopant in the glass matrix. The semi conducting nature of the glass network is found to increase due to the considerable increase in BO₃, MnO₆ structural units whenever B₂O₃ in the host glass is gradually replaced by MnO.     

Kerr studies of several tellurite glasses

Estimates of Kerr electrooptical sensitivity of several tellurite glasses are presented. The highest value of Kerr coefficient B ～ 190 × 10^?16 m V^?2 is registered for 0.6TeO₂–0.3TlO_0.5–0.1ZnO glass. This evidences the prospects of thallium–tellurite glass system for electrooptical applications. A gradual decrease of B from 41 × 10^?16 to 26 × 10^?16 m V^?2 in (1 ? x) TeO₂ – xNbO_2.5 system is revealed for x increasing from 0.1 to 0.15. No crystalline phase was found in that system, thus allowing attributing its Kerr sensitivity to the intrinsic properties of the glass matrix. The Kerr coefficient variation from 66 to 81 × 10^?16 m V^?2 was observed for 0.85TeO₂–0.15WO₃ glasses co-doped with small amounts of silver and cerium. The analysis of optical absorption spectra of several silver-containing tellurium–tungsten oxide glasses makes it possible to think that introducing cerium provokes formation of new mid-range orderings.     

EPR and optical studies of Mn2+ ions in Li2O–Na2O–B2O3 glasses – An evidence of mixed alkali effect

EPR and optical absorption spectra of 0.5 mol% MnO₂ doped xLi₂O–(30 − x)Na₂O–69.5B₂O₃ (5 ⩽ x ⩽ 25) glasses have been studied. The EPR spectra exhibit resonance signals characteristic of Mn²⁺ ions. The resonance signal at g ≅ 2.0 is due to Mn²⁺ ions in an environment close to octahedral symmetry, whereas the resonances at g ≅ 4.3 and g ≅ 3.3 are attributed to the rhombic surroundings of the Mn²⁺ ions. The ionic character (A), the number of spins participating in resonance (N), optical band gap energies (E_opt) and Urbach energies (ΔE) show the mixed alkali effect (MAE) with composition. The present study gives an indication that the size of alkalis we choose, is also an important contributing factor in showing the MAE. The variation of N with temperature obeys the Boltzmann law. The optical absorption spectra show a single broad band at ∼21 000 cm⁻¹ corresponding to the transition ⁶A_1g(S) → ⁴T_1g(G) which exhibits a blue shift with x. The theoretical values of optical basicity (Λ_th) have also been evaluated.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.     

High temperature spectroscopy of manganese and chromium doped glasses with the basic composition 16Na2O · 10CaO · 74SiO2

Glasses doped either with chromium or manganese or with both chromium and manganese were melted from the raw materials and studied by UV–vis–NIR spectroscopy. The measurements were carried out at temperatures in the range from 25 to 800 °C. In the glasses doped with only one transition metal oxide, the intensity of the absorption lines decreases and the full width at half maximum increases with increasing temperatures. Simultaneously, the peaks were shifted to larger wave numbers. In glasses doped with both chromium and manganese, the same behaviour was observed up to a temperature of 600 °C. At larger temperatures, the absorption band at 27 500 cm⁻¹ due to Cr⁶⁺ increases again, while the absorption band at 20 300 cm⁻¹ caused by Mn³⁺ decreases more strongly than in glasses solely doped with manganese. The behaviour observed was explained by the redox reaction Cr⁶⁺ + 3Mn²⁺ ⇄ Cr³⁺ + 3Mn³⁺ which is shifted to the left while increasing the temperature.     

White light emission from Eu3 +/Tb3 +/Tm3 + triply-doped aluminoborate glass excited by UV light

The Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses with the composition of CaO―Al₂O₃―B₂O₃―RE₂O₃ (RE = Eu,Tb,Tm) have been synthesized by melt quenching method. The photoluminescence of these Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses (CaAlB:RE^3 +) were studied and the emission spectra combining with blue, green and reddish orange bands were observed. Under 360 nm wavelength excitation the white light emission is achieved when the concentration (x) of Tm^3 + in Ca_0.931 ?xAlB:Eu^3 +_0.038,Tb^3 +_0.031,Tm^3 +_x glass is in the range of 0.0013-0.011 per mol matrix. In addition, the energy transfer (ET) between Tb^3 + and Eu^3 + ions in Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses was validated and the electric dipole–dipole interaction is responsible for the ET process of Tb^3 + → Eu^3 + at low concentrations. Hence, the Eu^3 +/Tb^3 +/Tm^3 + triply-doped aluminoborate glass could be a potential candidate for white LEDs.     

Structural properties of Cr2O3–Fe2O3–P2O5 glasses,Part I

The structural properties of xCr₂O₃–(40 − x)Fe₂O₃–60P₂O₅, 0 ⩽ x ⩽ 10 (mol%) glasses have been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The Raman spectra show that the addition of up to 5.3 mol% Cr₂O₃ does not produce any changes in the glass structure, which consists predominantly of pyrophosphate, Q¹, units. This is in accordance with O/P ≈ 3.5 for these glasses. The increase in glass density and T_g that occurs with increasing Cr₂O₃ suggests the strengthening of glass network. The Mössbauer spectra indicate that the Fe²⁺/Fe_tot ratio increases from 0.13 to 0.28 with increasing Cr₂O₃ content up to 5.3 mol%, which can be related to an increase in the melting temperature from 1423 to 1473 K. After annealing, the 10Cr₂O₃–30Fe₂O₃–60P₂O₅ (mol%) sample was partially crystallized and contained crystalline β-CrPO₄ and Fe₃(P₂O₇)₂. The SEM and AFM micrographs of the partially crystallized sample revealed randomly distributed crystals embedded in a homogeneous glass matrix. EDS analysis indicated that the glass matrix was rich in Fe₂O₃ (39.6 mol%) and P₂O₅ (54.9 mol%), but contained only 5.5 mol% of Cr₂O₃. These results suggest that the maximum solubility of chromium in these iron phosphate melts is 5.5 mol% Cr₂O₃.     

Thermal and optical properties of CuO–BaO–B2O3–P2O5 glasses

CuO-doped barium borophosphate glasses in a series of xCuO–(45 − x)BaO–10B₂O₃–45P₂O₅ in molar ratio with x = 0–15 mol% were prepared by a melt-quenching technique. All the glasses had excellent thermal stability against crystallization. Glass transition temperature, thermal expansion coefficient and molar volume decrease with increasing CuO concentration. The linear relationship between the absorption coefficient and CuO concentration exists for a peak wavelength in the transitions of ²A_1g → ²B_1g, ²B_2g → ²B_1g, ²E_g → ²B_1g. The relationship between the properties and glass structure evaluated by Raman spectroscopy is discussed.     

Microstructural analysis of Ga2S3–2MCl (M = K, Rb, Cs) glasses using Raman scattering

Raman scattering spectra of Ga₂S₃–2MCl (M = K, Rb, Cs) glasses have been conducted at room temperature. Based on the analysis of the local co-ordination surroundings of Cs⁺ ions, the similarities and differences of Raman spectra for the glass Ga₂S₃–2CsCl and the bridged molecular GaCl₃ were explained successfully. Through considering the effect of M⁺ ions on mixed anion units [GaS_4?xCl_x] and bridged units [Ga₂S_6?xCl_x] and the corresponding microstructural model, the Raman spectral evolution of the Ga₂S₃–2MCl (M = K, Rb, Cs) glasses was reasonably elucidated.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Glass composition dependence of luminescence due to Ge2+ center in germanate glasses

Germanate glasses were prepared by the melt-quenching method using an assembled hot-thermocoupler equipped in a sample chamber of a fluorescence spectrometer, and subsequently their luminescence and excitation spectra were measured. In the GeO₂ glass, luminescence bands due to the Ge²⁺ center appeared at the central wavelengths of 300 and 395 nm, their excitation bands being at 250 and 330 nm, respectively. In the (100 − x)GeO₂ − xM_mO_n glasses, for M_mO_n = B₂O₃ (x ≦ 50), SiO₂ (x ≦ 40), and Al₂O₃ (x ≦ 2), the luminescence intensity and therefore the amount of the Ge²⁺ center increased with increasing the content of M_mO_n, where M^(2n/m)+ ions (B³⁺, Si⁴⁺, and Al³⁺) have lower basicities than a Ge⁴⁺ ion. Contrarily, for M_mO_n = Li₂O (x ≦ 30), Na₂O (x ≦ 20), K₂O (x ≦ 20), CaO (x ≦ 20), SrO (x ≦ 3), BaO (x ≦ 15), ZnO (x ≦ 20), Ga₂O₃ (x ≦ 10), Sb₂O₃ (x ≦ 20), Bi₂O₃ (15 ≦ x ≦ 25), TiO₂ (x ≦ 3), and Nb₂O₅ (x ≦ 10), the luminescence intensity and the amount of the Ge²⁺ center rapidly decreased with increasing the amount of additives and disappeared, where M^(2n/m)+ ions (Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Ga³⁺, Sb³⁺, Bi³⁺, Ti⁴⁺, and Nb⁵⁺) have higher basicities than a Ge⁴⁺ ion.     

Redox reactions during temperature change in soda-lime–silicate melts doped with copper and iron or copper and manganese

Glasses with the base composition 16Na₂O · 10CaO · 74SiO₂ doped with copper and iron or copper and manganese were studied by high temperature UV–vis–NIR spectroscopy. The spectra exhibited distinct absorption bands attributed to the respective transition metal ions present (Cu²⁺, Fe²⁺, Fe³⁺, Mn³⁺). In glasses doped with only one polyvalent element, the absorption decreases linearly with increasing temperature, the absorption bands are shifted to smaller wave numbers and get broader. In glasses doped with two types of transition metals, the situation is the same up to a temperature of around 550 °C. At larger temperature, the Cu²⁺-absorption in glasses also co-doped with iron increases again, while in glasses doped with both copper and manganese the absorption is approximately the same as in glasses solely doped with copper. It is shown that this is due to redox reactions between polyvalent species. These reactions are frozen in at temperatures <550 °C.