Dysprosium doped alkali fluoroborate glasses—Thermal, structural and optical investigations

Thermal, structural and optical properties of Dy³⁺-doped alkali fluoroborate glasses with composition (in mol%), 49B₂O₃+25XO+25NaF+1Dy₂O₃ (where X=Li₂, Na₂, K₂, Mg and Ca), have been investigated. Thermal analysis revealed the homogeneous formation of the glasses. The FTIR spectra reveal that the glasses contain BO₃, BO₄ non-bridging oxygen atoms and strong OH⁻ bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross-section () and branching ratios (β_R) for the excited levels of Dy³⁺ ions in alkali fluoroborate glasses. The dependence of the spectral characteristics of Dy³⁺ ions due to compositional changes has been examined and reported.     

Optical absorption spectra of tripositive erbium ion in certain nitrate complexes

Optical absorption of Er³⁺ ion in Er(NO₃)₃·5H₂O, NH₄NO₃, Mg(NO₃)₂·6H₂O, KNO₃ and NaNO₃ complexes has been studied. The second derivative spectra of these Er³⁺ complexes exhibited splittings in the⁴ I _9/2,⁴ F _9/2,⁴ F _7/2,⁴ F _5/2 and² H _9/2 levels. These splittings have been tentatively explained as due to a cubic crystalline field. The partial derivatives for Er³⁺ ion have been calculated in terms of Racah (E ^k ) parameters. The results of a least squares fit of the energy levels and oscillator strengths of the bands are reported in terms of interaction parameters and Judd-Ofelt parameters. Radiative transition probabilities for various fluorescence levels are theoretically estimated. The lifetime of the⁴ G _11/2 level is found to be lowest in all nitrate complexes.     

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Yb³⁺ and M⁺ monovalent alkali ions (M⁺ = Li⁺, Na⁺, K⁺)-co-doped CaF₂ cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF₄ atmosphere. Structural and spectroscopic characterizations of Yb³⁺ in substitution of Ca²⁺ (absorption, emission and decay curves) were carried out to study the effect of M⁺ ions as charge compensators.     

An improved method for selective catalytic reduction of nitrogen oxides in exhaust gases

The selective catalytic reduction (SCR) of nitrogen dioxide in an air flow modeling the exhaust gas from an internal combustion engine is studied. Granulated V₂O₅ (13.5%)–MnO₂ (0.7–1.0%)/Al₂O₃ powder (AVK-10M catalyst) and ammonia injected into a SCR catalytic cell are used as a heterogeneous catalyst of NO₂ reduction and a reducing agent, respectively. If the efficiency of NO₂ removal is high enough and satisfies the requirements of the State Sanitary Standards for the maximum permissible concentrations of substances emitted into the atmosphere (\(MP{C_{N{O_2}}}\) = 0.085 mg/m³), the reducing agent (ammonia) is not completely consumed during SCR, so a considerable amount of NH₃ can be released into the atmosphere. Therefore, a strict control of both NO₂ and unreacted ammonia emissions is needed. The dependences of the concentrations of [NH₃] and [NO₂] on the [NH₃]/[NO₂] ratio for the model air flow passed through the AVK-10M granular heterogeneous catalyst are measured. It is found that the maximum degree of removal of NO₂ from the air takes place at [NH₃]/[NO₂] = 1.3. In the conventional process, the concentration of [NO₂] drop from 530.00 to 0.07 mg/m³, i.e., below the \(MP{C_{N{O_2}}}\). At the same time, the ammonia concentration increases to [NH₃] = 3.4 mg/m³, which becomes 85 times the \(MP{C_{N{O_2}}}\), 0.04 mg/m³. To remove unreacted ammonia from air flows, we developed [P–(SO₃ ^-)₂ · Me²⁺] sulfocationites, where Me are the Cu and/or Ca ions, P is a styrene–divinylbenzene copolymer. It is shown that the concentration of ammonia passed through the adsorption cell filled with a freshly sulfocationite drops below \(MP{C_{N{H_3}}}\) = 0.04 mg/m³. The dependences of the dynamic exchange capacity (DEC) before ammonia breakthrough for the [P–(SO₃ ^-)₂ · Cu²⁺] delta-sulfocationite on the air flow rate, [NH₃] concentration, and humidity are measured. The maximum value of the DEC, δ = 59.5 mg/cm³, is observed at an air flow velocity of 2.171 m/s, [NH₃] = 0.0035 mg/L, and 75% humidity. To illustrate practical applications of the proposed improved SCR method, it is shown that a 3-L replaceable [P–(SO₃ ^-)₂ · Cu²⁺] sorbent cartridge in a SCR exhaust gas purifier for a car internal combustion engine does not need replacement more frequently than every 50000 km.     

The determination of hopping rates and carrier concentrations in ionic conductors by a new analysis of ac conductivity

The a.c. conductivity σ(ω) of ionic materials takes the form, σ(ω) = σ(0) + Aωⁿ. The carrier hopping rate, ω_p, is obtained from the new expression σ(0) = A ω_pⁿ and the carrier concentration is estimated from σ(0). The contribution of creation and migration terms to the activation energy for conduction may be determined from the thermal activation of σ(0) and ω_p and the corresponding entropy terms quantified. Data have been analyzed for four widely different ionic materials: single crystal Na β-alumina, polycrystalline Li₄SiO₄, Ag₇l₄AsO₄ glass and Ca(NO₃)₂/KNO₃ glass and melt. For each, the carrier concentration and hopping rates have been obtained.     

Optical absorption and emission properties of Pr and Er in lithium cesium mixed alkali borate glasses

This article presents the optical absorption and emission properties of Pr³⁺ and Er³⁺ in mixed alkali borate glasses of the type 68B₂O₃·xLi₂O·(32-x)Cs₂O (where x=8, 12, 16, 20 and 24). The variation of Judd-Ofelt intensity parameters (Ω_λ), the peak wavelength of the hypersensitive transitions, radiative transition probabilities (A_rad) and peak emission cross-sections (σ_p) with x in the glass matrix have been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes (τ_R) of certain excited states of both Pr³⁺ and Er³⁺ in lithium cesium mixed alkali borate glasses are reported. Branching ratios (β) and integrated absorption cross-sections (Σ) for certain important transitions are presented. Peak stimulated emission cross-sections (σ_p) are calculated for the observed emission peaks of Pr³⁺ and Er³⁺ ions in this glass matrix.     

Structure and phase transformation of alkali silicate melts analysed by Raman spectroscopy

Raman spectra of binary alkali silicates were measured at various temperatures from 1300°C to room temperature to investigate the relation between structural change and phase transformation phenomena. Distribution of structural units of Q ⁿ was estimated at each temperature by the deconvolution of spectra based on the equilibrium 2Q³ ? Q² + Q⁴. The Q ⁿ distributions of sodium and potassium silicate systems strongly depend on temperature and the equilibrium shifts to the left-hand side with decreasing temperature, but those of lithium silicate system were less sensitive to the temperature variation. In alkali disilicates (33?mol%?R₂O–67?mol%?SiO₂, where R=Li, Na or K), the Q ⁿ distributions near the melting point were independent of alkali ion species, and they held the relation [Q²]?=?[Q⁴]?≈?[Q³]/4. This means that two of 6Q³ units (six-memberd ring) in crystals are transformed into a pair of Q² and Q⁴ in the melting process. Below the melting point, the Q ⁿ distribution in lithium disilicate melt remained while, in sodium and potassium disilicate melts, [Q³] increased with decreasing temperature. Crystallization of the alkali disilicate melts is discussed considering the configuration entropy of Q ⁿ units. In 25?mol%?Li₂O–75?mol%?SiO₂, which is in the range of the immiscibility dome, the Q ⁿ distribution was maintained even when phase separation occurs in the cooling process.     

Absorption and emission properties of Nd in lithium cesium mixed alkali borate glasses

Lithium cesium mixed alkali borate glasses of the composition 67B₂O₃·xLi₂O·(32−x)Cs₂O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd₂O₃ were prepared by melt quenching. The absorption spectra of Nd³⁺ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (A_T), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd³⁺ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τ_R) are estimated for certain excited states of Nd³⁺ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σ_p) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses.     

Magneto-electrogyration in cubic Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2

The simultaneous application of electric and magnetic fields on single crystals of Sr-, Ba-and Pb-dinitrate yields an additional term to the pure electrogyration and Faraday effect. The symmetric part of the fourth-rank tensor of this magneto-electrogyration has been completely determined with the aid of a high-resolution computer-aided polarimetric device. In Pb(NO₃)₂ a maximum magneto-electrogyration of about 10% of the magnitude of electrogyration is observed when a magnetic field of 1000 kA/m (1.2 Tesla) is applied along [111]. The effects in Sr(NO₃)₂ and Ba(NO₃)₂ are much smaller. Index of refraction, electrogyration, Faraday effect, and the new magneto-electrogyration obey the same sequence: Pb(NO₃)₂ > Ba(NO₃)₂ > Sr(NO₃)₂.     

Comparitive study of structure changes with temperature in univalent and divalent ionic nitrate crystals

The temperature dependence of the d.c. resistivity and dielectric constant of polycrystalline samples of Pb(NO₃)₂, Ba(NO₃)₂ and Sr(NO₃)₂ were found to show anomalies in the high temperature region. In addition, sharp peaks were obtained in both differential thermal analysis (DTA) and thermomechanical analysis (TMA) curves in the same temperature range. The observed anomalies were attributed to orientational disorder of the nitrate group leading to an order-disorder phase transition which is reported here for the first time. A comparison is made between the role of NO₃^?ions in both the divalent and univalent nitrates, taking NaNO₃ as representative. The TMA curve for Sr(NO₃)₂ showed a pronounced peak at 325°C. This peak was related to a sudden increase in the expansion coefficient associated with the rotation of the NO₃^? group leading to a solid state phase transformation. Energy diagrams describing the conduction mechanism and showing a fractionization of energy barriers in the case of divalent nitrates are introduced.     

Drift study of the products formed by radiolysis and photolysis of alkaline nitrates

The products of the radiolysis and photolysis of crystalline sodium, potassium, rubidium, cesium nitrates have been investigated by the diffuse reflectance infrared Fourier transform spectroscopy. The bands in the 1260-1220 and 804-809 cm^?1 regions observed after the n -irradiation and photolysis by a light with the wave length 253.7 nm of crystalline alkali nitrates were identified as the vibrational modes of NO^? ₂ x ₃ and x ₂, respectively. The frequency of the x ₃ oscillation of nitrite ions decreases from 1260 cm^?1 up to 1220 cm^?1 with the increase of the atomic weight or polarizability of a cation. The detection limit of the nitrite ions (1 ‐ 10^?7 mol g^?1) for the diffuse reflection method has been determined. The bands observed in KNO₃, RbNO₃ and CsNO₃ spectra in the 947-940 and 722-737 cm^?1 regions appearing only after photolysis are due to stretch oscillations of the peroxide bond O-O and wagging oscillations of the -ON=O group of peroxynitrite accordingly.     

89Yttrium nuclear magnetic resonance studies

With a Fourier-transform spectrometer, especially developed for nuclei with weak NMR signals, the lines of⁸⁹Y have been investigated in aqueous solutions of Y(NO₃)₃, YCl₃, and Y(ClO₄)₃. The concentration dependence of the chemical shifts of the⁸⁹Y resonance frequencies in these solutions were measured. Using this dependence, the Larmor frequency of the⁸⁹Y³⁺ ion solely surrounded by water was determined by extrapolation. The Larmor frequency of⁸⁹Y was referred to those of²H,³⁹K, and⁷³Ge with high accuracy. The magnetic moment of the⁸⁹Y³⁺ ion purely surrounded by H₂O molecules is μ(⁸⁹Y³⁺) = ?0.1368523(4) μ_N. The concentration dependence of Y(NO₃)₃ solutions in D₂O yields the solvent isotope effect δ(⁸⁹Y³⁺ in D₂O)?δ(⁸⁹Y³⁺ in H₂O)= ?(4.3±0.5)ppm. The⁸⁹Y relaxation times T₁ and T₂ of a 3 molal aqueous Y(NO₃)₃ solution were determined in the pH range ?0.5...+1.25. T₁ 190...90 s is nearly constant in this range, whereas the transverse relaxation rate T₂ ^?1 increases strongly with increasing pH; this effect seems to be due to the chemical exchange of the hydrated Y³⁺ ion between a monomer and a polymer site.     

New sonochemiluminescence involving solvated electron in Ce(III)/Ce(IV) solutions

The moving single-bubble sonoluminescence of Ce³⁺ in water and ethylene glycol solutions of CeCl₃ and (NH₄)₂Ce(NO₃)₆ was studied. As found, a significant part of intensity of the luminescence (100% with cerium concentration less than 10^–4 M) is due to the sonochemiluminescence. A key reaction of sonochemiluminescence is the Ce⁴⁺ reduction by a solvated (or hydrated in water) electron: Ce⁴⁺ + e_s (e_aq) → *Ce³⁺. Solvated electrons are formed in a solution via electrons ejection from a low-temperature plasma periodically generated in deformable moving bubble at acoustic vibrations. Reactions of heterolytic dissociation of solvents make up the source of electrons in the plasma. In aqueous CeCl₃ solutions, the Ce⁴⁺ ion is formed at the oxidation of Ce³⁺ by OH radical. The latter species originates from homolytic dissociation of water in the plasma of the bubble, also penetrating from the moving bubble into the solution. The sonochemiluminescence in cerium trichloride solutions are quenched by the Br⁻ (acceptor of OH) and H⁺ ions (acceptor of e_aq). In water and ethylene glycol solutions of (NH₄)₂Ce(NO₃)₆, the sonochemiluminescence also quenched by the H⁺ ion. The sonochemiluminescence in CeCl₃ solutions is registered at [Ce³⁺] ≥ 10^–5 M. Then the sonochemiluminescence intensity increases with the cerium ion concentration and reaches the saturation plateau at 10^–2 M. It was shown that sonophotoluminescence (re-emission of light of bubble plasma emitters by cerium ions) also contributes to the luminescence of Ce³⁺ in solutions with [Ce³⁺] ≥ 10^–4 M. If the cerium concentration is more than 10^–2 M, a third source contributes to luminescence, viz., the collisional excitation of Ce³⁺ ions penetrating into the moving bubble.     

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M₃[Fe(C₃H₂O₄)₃].4H₂O(M=Li, Na, K, NH₄) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, NH₄ ⁺). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.     

New aspects on the dielectric properties of the alkali halides with divalent impurities

Dielectric losses were measured in the following crystals NaCl+ (Mg²⁺, Co²⁺, Ni²⁺, Sr²⁺, Ca²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Ba²⁺, Pb²⁺), KCl + (Ca²⁺, Sr²⁺, Ba²⁺, ²⁺, Pb²⁺) and KBr + (Sr²⁺, Ba²⁺) in the frequency region 5–500 kHz. It was found that when the divalent cation impurity has an electronic configuration similar to the inert gases (1) no observable deviation from simple Debye theory exists (2) the activation energy Φ increases linearly with the ionic radius of the impurity.The above observations (1) and (2) do not hold when the divalent cation impurity has d-electrons in the outer subshell.     

RAMAN STUDY ON (Pb) CENTERS IN SINGLE CRYSTALS OF ALKALI HALIDES DOPED WITH LEAD

Low frequency modes were observed in a series of alkali halides doped with lead after X-irradiation at 77K. The peak positions of the Raman signals are at 34cm^-1 for NaCl:Pb²⁺, 30cm^-1 for KCl:Pb²⁺,28cm^-1 for RbCl:Pb²⁺ and 22cm^-1 for KBr:Pb²⁺. They are assigned to the inelastic light scattering caused by the local vibration of X^-_i (Pb⁺) center, which consists of an interstitial halogen ion stabilized by a substitutional ion Pb⁺ . Polarized Raman measurements and Behavior Typer(BT) analysis show that the symmetry of the X^-_i (Pb⁺) center belongs to the point group C_3v A structure model of the X^-_i (Pb⁺) center is proposed based on the Raman data and the result of BT analysis.     

High and low frequency Jonscher behaviour of an ionically conducting glass

The ac conductivity of an ionically conducting glass, 0.4Ca(NO₃)₂:0.6KNO₃, is reexamined. The data is seen to exhibit a Jonscher, power-law dependence on frequency; however, two power-law expressions are required to describe the ac response σ=G₀+A₁ω^n₁+A₂ω^n₂. An explanation is advanced involving the formation of clusters within the glass on cooling.     

Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO₃)₂(CH₃OH)](NO₃) and [NdL(NO₃)₂(CH₃OH)](NO₃) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV-vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol⁻¹, ΔS=56.54 J mol⁻¹ K⁻¹ for [PrL(NO₃)₂(CH₃OH)](NO₃) and ΔH=−24.63 kJ mol⁻¹, ΔS=22.07 J mol⁻¹ K⁻¹ for [NdL(NO₃)₂(CH₃OH)](NO₃)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes-BSA system. The binding average distance between complexes and BSA was obtained on the basis of Förster's theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.     

New alkali antimonate glasses

Glass formation has been investigated in ternary systems Sb₂O₃-PbO-M₂O in which M is alkali Li, Na and K and antimony oxide is the glass former. Alkali elements were introduced as carbonates. The size of the glass forming region is enlarged as alkali ionic radius increases. Binary Sb₂O₃-M₂O glasses were obtained: (100−x) Sb₂O₃-xLi₂O, (10<x<30), (100−x) Sb₂O₃-xNa₂O, (10<x<70), and (100−x) Sb₂O₃-xK₂O, (10<x<90). In ternary systems, PbO content could reach 60 mol%. Temperatures of glass transition, T_g, onset of crystallization, T_x, and maximum of crystallization, T_p, have been measured using differential scanning calorimetry. Depending on composition, glass transition temperature ranges from 240 to 330 °C. The incorporation of alkali oxide increases T_g while lead oxide has the reverse effect. Thermal stability range (T_x-T_g) was usually between 65 and 266 °C, while no crystallization exotherm was observed in some cases. Density and thermal expansion increases as lead concentration increases. Optical transmission has been measured. The UV cut-off depends on alkali content: samples are yellow and turn green for large K and Na content. These glasses have potential applications as low phonon energy glasses for infrared transmission or active devices.     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.