Interionic Distance Research Articles

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium (Eu3+) doped glasses of chemical compositions (55−x)B2O3:10SiO2:25Y2O3:10CaO:xEu2O3, where x denotes mol% and ranges 0 ≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique. Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu2O3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence, X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt (JO) intensity parameters (Ωλ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability (AR), branching ratio (βR), stimulated cross section emission (σ) and radiative lifetime (τR) for 5D0 → 7FJ (J = 0,1,2,3 and 4) transitions. The decay rate of 5D0 fluorescent level for all the glass samples was single exponential. Lifetimes of the 5D0 level were decreased with increasing concentrations of Eu3+ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates (x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu3+ doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.

An analysis of the fluctuation potential in the modified Poisson-Boltzmann theory for restricted primitive model electrolytes

An approximate analytical solution to the fluctuation potential problem in the modified Poisson-Boltzmann theory of electrolyte solutions in the restricted primitive model is presented. The solution is valid for all inter-ionic distances, including contact values. The fluctuation potential solution is implemented in the theory to describe the structure of the electrolyte in terms of the radial distribution functions, and to calculate some aspects of thermodynamics, viz., configurational reduced energies, and osmotic coefficients. The calculations have been made for symmetric valence 1:1 systems at the physical parameters of ionic diameter $4.25 \times 10^{-10}$ m, relative permittivity 78.5, absolute temperature 298 K, and molar concentrations 0.1038, 0.425, 1.00, and 1.968. Radial distribution functions are compared with the corresponding results from the symmetric Poisson-Boltzmann, and the conventional and modified Poisson-Boltzmann theories. Comparisons have also been done for the contact values of the radial distributions, reduced configurational energies, and osmotic coefficients as functions of electrolyte concentration. Some Monte Carlo simulation data from the literature are also included in the assessment of the thermodynamic predictions. Results show a very good agreement with the Monte Carlo results and some improvement for osmotic coefficients and radial distribution functions contact values relative to these theories. The reduced energy curve shows excellent agreement with Monte Carlo data for molarities up to 1 mol/dm$^{3}$.

Mean force potential of interaction between Na+ and Cl− ions in planar nanopores in contact with water under pressure

The mean force potential (MFP) of interaction between counterions Na+ and Cl− in a planar nanopore with structureless hydrophobic walls is calculated via computer simulation under the condition that the nanopore is in contact with water at an external pressure that exceeds the saturation pressure but remains insufficient to fill the nanopore with water. For a nanopore with a liquid phase, the MFP dependence on the interionic distance indicates the dissociation of an ion pair into two hydrated ions in a nanopore that is not completely filled with water. Fluctuations in the number of water molecules drawn into the interionic space decisively influence the dissociation. The attraction between counterions, averaged over thermal fluctuations, depends largely on the pore width and grows as the shielding of the ions’ electric field by water molecules in a narrow pore diminishes. The contributions from energy and entropy to the free energy of hydration are analyzed.

Network structure analysis of modifier CdO doped sodium borate glass using FTIR and Raman spectroscopy

Ternary oxide glass system of chemical composition of 80B2O3–(20-x)Na2O–xCdO (where x=0, 2, 4, 6, 8, 10, 12, 14mol%) have been prepared by conventional melting and quenching method. The micro structural and morphological investigation of synthesized glass samples were carried out by using XRD, FE-SEM. The supporting physical and composition dependent properties such as experimental and theoretical density, molar volume, oxygen packing density, ionic concentration, interionic distance and polaron radius were determined. Density of glass samples increases, while molar volume decreases with the increasing cadmium oxide concentration from 0 to 14mol%. X-ray diffraction profiles and FE-SEM images confirmed amorphous nature of investigated glass samples. Elemental analysis and information about the chemical composition of glass matrices have been ascertained by using EDS spectra. The interpretation of functional groups [BO3] and [BO4] units present in the oxide glass was simulated by using deconvoluted Raman spectra and FTIR spectroscopy. BO stretching, metal cation active vibrational modes and bending vibrations of BOB linkage in borate glass network are cross verified by using FTIR and Raman spectroscopy.

Modulated single band red upconversion luminescence from Ho3+ doped nanoparticles with two-wavelength excitation

Single band red upconversion luminescence has the potential applications from science to engineering, however, suffered from low luminescence efficiency. Single band enhanced red upconversion luminescence from NaYF4: Ho nanoparticles has been realized with the modulation of two-wavelength excitation and the administration of cross relaxation between 5F4, 5S2 → 5F5 and 5I7 → 5I6 of Ho3+. Compared to the sum intensities with single-wavelength excitation at 975 nm and 1150 nm, the upconversion intensity for red and green luminescence is enhanced by the factors of 13.04 and 0.46 respectively with two-wavelength excitation. The red/green ratio of upconversion luminescence intensity is modulated from 15.46 to 115.03 by controlling the interionic distance and cross relaxation between Ho3+ ions. The microscopy mechanism of single band enhanced red upconversion luminescence with two-wavelength excitation at 1150 nm and 975 nm is ascribed to the ground state absorption of 1150 nm and excited state absorption of 975 nm, which was explored by power depended upconversion luminescence intensities, excitation spectra, and absorption spectrum. Besides, single band red upconversion luminescence from NaYF4: 10%Ho nanoparticles with the two-wavelength excitation shows the comparable intensity with that from NaYF4: 20%Yb, 2%Ho nanoparticles excited by 975 nm. Our results might provide a new method for the single band red upconversion luminescence with the applications in biology and three-dimensional displays.

Electronic polarizability, optical basicity and interaction parameter for Nd2O3 doped lithium–zinc–phosphate glasses

The Nd3+-doped lithium–zinc–phosphate glasses were prepared by means of conventional melt quenching method. X-ray diffraction results confirmed the glassy nature of the studied glasses. The physical parameters such as the density, molar volume, ion concentration, polaron radius, inter-ionic distance, field strength and oxygen packing density were calculated using different formulae. The transmittance and reflectance spectra of glasses were recorded in the wavelength range 190–1200 nm. The values of optical band gap and Urbach energy were determined based on Mott–Davis model. The refractive indices for the studied glasses were evaluated from optical band gap values using different methods. The average electronic polarizability of the oxide ions, optical basicity and an interaction parameter were investigated from the calculated values of the refractive index and the optical band gap for the studied glasses. The variations in the different physical and optical properties of glasses with Nd2O3 content were discussed in terms of different parameters such as non-bridging oxygen and different concentrations of Nd cation in glass system.

Ca2+ -Cl- Association in Water Revisited: the Role of Cation Hydration.

We investigate the dissociation of a Ca2+ -Cl- pair in water using classical molecular dynamics simulations with a polarizable interaction potential, parameterized from ab initio calculations. By computing the potential of mean force as a function not only of the interionic distance but also of the coordination numbers by water molecules, we show that it is necessary to use a collective variable describing the cation hydration in order to capture the dissociation mechanism. In the contact ion pair, the Ca2+ cation has a first coordination sphere containing 5 or 6 water molecules. The minimum free-energy path for dissociation involves a two-step process: First one or two additional water molecules enter the cation coordination shell, increasing the coordination number up to 7 with an almost fixed interionic distance. Then the dissociation of the ionic pair occurs at this fixed coordination number.

Determination of inter-ionic and intra-ionic interactions in a monofluorinated imidazolium ionic liquid by a combination of X-ray crystallography and NOE NMR spectroscopy.

We report the very first application of a Transient 1D 1 H{19 F} NOE NMR experiment in neat ionic liquids. In comparison with classical 2D HOESY NMR spectroscopy, a substantial reduction in measurement time is gained with comparable quality and information content of the spectra. In combination with classical X-ray crystallography, we have applied this technique for the determination of inter-ionic distances (i.e. probabilities of presence) utilizing an ionic liquid containing a monofluorinated imidazolium cation. Copyright © 2017 John Wiley & Sons, Ltd.

Physical and optical properties for Nd2O3 doped lithium-zinc-phosphate glasses

The Nd3+-doped lithium-zinc-phosphate glasses were prepared by means of conventional melt quenching method. X-ray Diffraction results were confirmed the glassy nature of the studied glasses. The physical parameters such as the density, molar volume, ion concentration, polaron radius, inter-ionic distance and field strength were calculated using different formulae. The absorption, transmittance and reflectance spectra of glasses were recorded in the wavelength range 190–1200nm. Bonding of Nd3+ ions with surrounding ligands is found to be covalent. Dispersion parameters such as: single oscillator energy, dispersion energy, the ratio of carrier concentration to the electron effective mass and the lattice dielectric constant are determined. Electronic polarizability of the oxide ion and optical basicity of these glasses are calculated from the values of optical band gap. Effects of doping Nd2O3 on these properties are investigated and interpreted.

Mechanisms for ion retention in molecular water clusters in a planar nanopore against the background of thermal fluctuations

The Monte Carlo method has been used to calculate the potential of mean force for Na+ and Cl− ions interacting in model planar nanopores with structureless walls under the conditions of the material contact with water vapor at room temperature and above water boiling point. The interactions have been described using a detailed many-body model calibrated with respect to experimental data on the free energy of attachment reactions and the results of quantum-chemical calculations. Dissociation becomes possible when the vapor density increases as a sufficient number of molecules are pulled into the field of the ions. The dissociation proceeds sooner under the conditions of the nanopore than in bulk water vapor. Hydration decreases the energy of the dissociated state; however, the entropy component of the free energy partly compensates for the decrease in the internal energy, thereby increasing the stability of a contact ion pair. After the dissociation of a contact ion pair (CIP), ions are retained within a cluster in the state of a solvent-separated ion pair (SSIP). Fluctuations in the number of pulled-in vapor molecules, which are correlated with fluctuations in the interionic distance, stabilize the SSIP states with respect to recombination, while a decrease in the screening of the field of ions under the conditions of the nanopore stabilize the SSIP states with respect to cluster decay. The conditions of the nanopore stimulate the passage of an ion pair from the CIP to the SSIP state due to the rearrangement of the statistical weights in favor of molecules being located in the interionic gap. Thus, under the conditions of the nanopore, the stability of the SSIP states increases with respect to both the recombination of the ions and the decay of the ion-molecular associate.

Effect of Co2+ ions on the ligand field, optical, and structural properties of ZnLiB glasses

Glass systems with composition x CoO-(25-x) ZnO-75 Li2B4O7, (where x=0, 0.5, 1, 2 and 3mol%) were prepared by conventional melt-quenching technique. The density and molar volume of the glass systems were determined in order to study their structures. The physical parameters such as ionic concentration, interionic distance, polaron radius, field strength, molar refractivity, and metallization were estimated. The decrease in the optical basicity Ʌth suggests that the covalence of the glass increases. The crystal field (10Dq) and interelectronic repulsion (B, C) parameters were evaluated. FT-IR spectra of the glasses showed vibration modes corresponding to stretching of BO3 and BO4 units. It was found that N4 decreases with increasing the CoO content. This is due to the increased intensity of the vibrational bands associated to BO3 units at the expense of the BO4 units, which led to an increased number of NBOs.

A Novel Barium Borate Glasses for Optical Applications

Optical properties of xBaO–5ZnO–5MgO–14Na2O–1Li2O–(75x)B2O3 glasses (where x = 0, 10, 20, 30, 40, and 50 mol %) were performed using a UV-Visible spectrophotometer in the spectral range 190–1100 nm. Various optical parameters such as optical band gap, Urbach energy, refractive index, electronic polarizability and optical basicity were deduced. The glassy phase of the samples was checked using X-ray diffraction. The density was measured at room temperature by the conventional Archimedes principle. Additionally, many structural parameters like, molar volume, inter-ionic distance, barium ion concentration and oxygen packing density were calculated based on the density results. Fourier Transform Infrared Spectroscopy (FTIR) in the wavenumber range 1600–400 cm −1 was carried out to identify the spectral contribution of each component on the structure and to point out the role of the barium ions as a modifier of the glass network. The results reflected that addition of BaO in ZnO–MgO–Na2O–Li2O–B2 O 3 glasses creates of non-bridging oxygen in the glass network. The present glasses possess high refractive index and high electronic polarizability. Hence, the reported glasses can find applications in the areas of optical materials.

Stabilization of ultra-small [Ag2]2+ and [Agm]n+ nano-clusters through negatively charged tetrahedrons in oxyfluoride glass networks: To largely enhance the luminescence quantum yields.

Herein, three different silver species were stably formed in SiO2-Al2O3-B2O3-Na2O-ZnF2-CaF2 glasses and were identified by their characteristic luminescence bands: violet blue luminescence (Ag+: 4d95s1 → 4d10), green white molecular fluorescence (molecule-like [Agm]n+, named ML-Ag) and orange molecular fluorescence ([Ag2]2+ pairs). Due to the relatively low aggregation degrees of [Agm]n+ and [Ag2]2+, non-radiative transitions were highly suppressed, and the PL quantum yields (QYs) of ML-Ag and [Ag2]2+ pairs reached 73.7% and 89.7%, respectively. The substitution of 0.5B2O3-0.5Na2O with SiO2 promoted the partial reduction of Ag+ to Ag0 and the subsequent aggregation of Ag+ and Ag0 to form [Agm]n+ (ML-Ag). The absence of Na2O also resulted in an increasing amount of Ag+-Ag+ pairs with closing interionic distance to form [Ag2]2+ in glass. According to the X-ray photoelectron spectra (XPS) and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra, a solubility strategy and a charge compensation model were proposed to describe the transformations between different silver species. The formation of ML-Ag was further controlled via the solubility of Ag+ in glass, whereas [Ag2]2+ centers could be effectively produced by lowering the total amount of other competitive charge compensators, such as Na+, or by introducing negatively charged [BO4]-, [AlO4]-, and [ZnO4]2- tetrahedrons into the glass matrix.

Synthesis of transparent Er-doped fluorotellurite glass–ceramics through controlled crystallization

This work presents a detailed study of the preparation and microstructure of transparent glass–ceramics obtained from a TeO2−ZnO−ZnF2 fluorotellurite glass doped with ErF3. The determination of nucleation and crystal growth rate-like curves allows establishing a narrow temperature range (340–350 °C) for a controlled crystallization. Thereafter, a crystalline phase was grown through a two-step heat treatment: 10–20 h at a temperature slightly above the glass transition temperature, followed by a 2.5–3 h treatment at 340 °C. Structural analysis showed the nucleation of ErF3 nanocrystals (NCs) with a typical size of ≈50 nm that were homogeneously distributed in the glass matrix. The resulting glass–ceramic material remains highly transparent, with a small crystalline to amorphous ratio; yet the presence of ErF3 NCs has a large impact on the photoluminescence response of Er3+ ions. Upconverted visible emission is analyzed under 980 nm excitation: red emission from the 4F9/2 level is dramatically enhanced with respect to green 2H11/2, 4S3/2 → 4I15/2 hypersensitive transitions. The observed behaviour is attributed to the presence of Er3+ ions in the NCs, which are sites with lower phonon energy than the glass matrix. Moreover, the shorter inter-ionic distance between Er3+ ions in the NCs eases energy transfer between them.

Sintering effect on structural, magnetic and optical properties of Ni0.5Zn0.5Fe2O4 ferrite nano particles

Ni0.5Zn0.5Fe2O4 nano ferrite particles have been prepared by mechanical alloying via high energy ball milling and sintered at different temperatures from 700°C to 1000°C. Spinel structure is confirmed from the analysis of XRD data. Rietveld refinement method is employed to refine the XRD powder data and the structural parameters are calculated from the refinement. Small amount of hematite phase is found in all samples. The SEM, EDAX and XRF analysis reveals respectively the morphology, stoichiometric composition and purity of the powder samples. Using Maximum Entropy Method (MEM) the values of the bond strength between various sites interactions in ferrites are evaluated and compared with theoretical predictions of strengthening/weakening of various sites interactions from the values of interionic distances and interionic bond angles. Ferromagnetic nature of the samples is confirmed from the vibrating sample magnetometer study. The obtained low saturation magnetization values are attributed to presence of second phase. The optical band gap energy of the samples was determined by using UV–VIS techniques.

Enhancement in Curie Temperature with Magnesium Substituted in Sintered Mg<sub>x</sub>Mn<sub>1-x</sub>Fe<sub>2</sub>O<sub>4</sub> Pellets of Nanopowders

Ferrites nanopowder of spinel MgxMn1-xFe2O4 (with x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) synthesized by the coprecipitation method and pellets of nanopowder sintered at temperature 1250 °C. The X-ray diffraction results confirmed the single phase formation of the samples. The lattice constant and interionic distances decreased with increase in magnesium content that can be originated by strengthening of A–B interaction. The substitution effect of nonmagnetic Mg2+ ions was studied on Curie temperature of sintered pellets. Curie temperature measurements exhibit increasing trend with increase in magnesium content. Enhancement in Curie temperature can be explained on the basis of strengthening of A–B interaction and Neel’s two sub-lattice models.

Water vapor nucleation on ion pairs under the conditions of a planar nanopore

Computer simulation has been employed to study the effect of a confined space of a planar model pore with structureless hydrophobic walls on the hydration of Na+Cl– ion pairs in water vapor at room temperature. A detailed many-body model of intermolecular interactions has been used. The model has been calibrated relative to experimental data on the free energy and enthalpy of the initial reactions of water molecule attachment to ions and the results of quantum-chemical calculations of the geometry and energy of Na+Cl– (H2O) N clusters in stable configurations, as well as spectroscopic data on Na+Cl– dimer vibration frequencies. The free energy and work of hydration, as well as the adsorption curve, have been calculated from the first principles by the bicanonical statistical ensemble method. The dependence of hydration shell size on interionic distance has been calculated by the method of compensation potential. The transition between the states of a contact (CIP) and a solvent-separated ion pair (SSIP) has been reproduced under the conditions of a nanopore. The influence of the pore increases with the hydration shell size and leads to the stabilization of the SSIP states, which are only conditionally stable in bulk water vapor.

Tuning Mn4+ Red Photoluminescence in (K,Rb)2Ge4O9:Mn4+ Solid Solutions by Partial Alkali Substitution

We report on intense photoluminescence from materials of the (Rb,K)2Ge4O9:Mn4+ solid solution as a novel class of red‐emitting oxide phosphors. In these compounds, luminescence originates from a virtually ideal substitution of Mn4+ for Ge4+ on octahedral lattice sites which are well‐isolated from each other within the unit cell by intermediate GeO4 species. Complete isostructural substitution of K for Rb is possible across the join. The associated slight shrinkage of the unit cell has only little effect on the apparent Mn4+ interionic distance, but enables tuning of the absorption cross section and of the band structure, hence, of the emission lifetime, of the excitation band shape, and of emission quantum yield. Partial substitution was also found to reduce thermal quenching of the Mn4+‐related emission, apparently due to the lower polarizability of the K+ ion. In addition, random substitution of Rb by K enables modulation of the interaction of Mn4+ with its surrounding field at lower symmetry, leading to increasing emission bandwidth, i.e., 595 cm−1 in K1.5Rb0.5Ge4O9:Mn4+ vs 558 or 578 cm−1 in Rb2Ge4O9:Mn4+ or K2Ge4O9:Mn4+ respectively.

Preparation and thermophysical properties of Sm2YbTaO7 and Sm2YTaO7

Sm2YbTaO7 and Sm2YTaO7 ceramics were synthesized by solid reaction method at 1600°C for 10h. Crystal phases have been identified by X-ray diffraction, and their thermal conductivities and thermal expansion coefficients were measured using a laser flash method and the pushing-rod technology, respectively. Results indicate that Sm2YbTaO7 and Sm2YTaO7 exhibit a typical defect fluorite-type crystal structure. Compared to Sm2YTaO7, Sm2YbTaO7 has lower thermal conductivity due to the higher atomic weight difference between the substituted and substituting atoms. The thermal expansion coefficient of Sm2YbTaO7 is greater than that of Sm2YTaO7 due to its elongated average interionic distance. Their thermal conductivities are much lower than that of YSZ, and their thermal expansion coefficients are very close to that of YSZ. The synthesized ceramics also exhibit excellent phase stability in the temperature range from ambient to 1200°C.

Absorption Spectroscopy Analysis of Calcium-Phosphate Glasses Highly Doped with Monovalent Copper.

CaO-P2 O5 glasses with high concentrations of monovalent copper ions were prepared by a simple melt-quench method through CuO and SnO co-doping. Spectroscopic characterization was carried out by optical absorption with the aim of analyzing the effects of Cu(+) ions on the optical band-gap energies, which were estimated on the basis of indirect-allowed transitions. The copper(I) content is estimated in the CuO/SnO-containing glasses after the assessment of the concentration dependence of Cu(2+) absorption in the visible region for CuO singly doped glasses. An exponential dependence of the change in optical band gaps (relative to the host) with Cu(+) concentration is inferred up to about 10 mol %. However, the entire range is divided into two distinct linear regions that are characterized by different rates of change with respect to concentration: 1) below 5 mol %, where the linear dependence presents a relatively high magnitude of the slope; and 2) from 5-10 mol %, where a lower magnitude of the slope is manifested. With increasing concentration, the mean Cu(+) -Cu(+) interionic distance decreases, thereby decreasing the sensitivity of monovalent copper for light absorption. The decrease in optical band-gap energies is ultimately shown to follow a linear dependence with the interionic distance, suggesting the potential of the approach to gauge the concentration of monovalent copper straightforwardly in amorphous hosts.