Interionic Distance Research Articles

Suppressed concentration quenching and tunable photoluminescence in Eu2+-activated Rb3Y(PO4)2 phosphors for full-spectrum lighting

Highly efficient inorganic phosphors are desirable for lighting-emitting diode light sources, and increasing the doping concentration of activators is a common approach for enhancing the photoluminescence quantum yield (PLQY). However, the constraint of concentration quenching poses a great challenge for improving the PLQY. Herein, we propose a fundamental design principle by separating activators and prolonging their distance in Eu2+-activated Rb3Y(PO4)2 phosphors to inhibit concentration quenching, in which different quenching rates are controlled by the Eu distribution at various crystallographic sites. The blue-violet-emitting Rb3Y(PO4)2:xEu (x = 0.1%–15%) phosphors, with the occupation of Rb1, Rb2 and Y sites by Eu2+, exhibit rapid luminescence quenching with optimum external PLQY of 10% due to multi-channel energy migration. Interestingly, as the Eu concentration increases above 20%, Eu2+ prefer to occupy the Rb1 and Y sites with separated polyhedra and large interionic distances, resulting in green emission with suppressed concentration quenching, achieving an improved external PLQY of 41%. Our study provides a unique design perspective for elevating the efficiency of Eu2+-activated phosphors toward high-performance inorganic luminescent materials for full-spectrum lighting.

Surface Tension of Simple Molten Salts: Insight from a Charged Hard Sphere Model.

Surface tension of molten salts is rooted in many important phenomena in physical chemistry. We develop an analytical theory for the surface tension of molten salts, where the molten salt is described by a restricted primitive model electrolyte consisting of charged hard spheres, and surface tension is related to the formation of a cavity in the electrolyte. The integral equation theory is applied to the restricted primitive model electrolyte to derive an analytical formula of the cavity formation energy. The scaling relation of the cavity formation energy is further combined with morphological thermodynamics theory to determine the formula for surface tension. According to our formula, surface tension consists of a positive hard sphere contribution and a negative electrostatic contribution. Using the molar mass, interionic distance, density, and temperature as the input, our theory leads to a good prediction of surface tension of more than 16 molten salts at their melting point without introducing any adjustable parameters.

Exploring the structural, optical and photoluminescence of novel terbium-doped barium borosilicate glasses for high-performance technologies

The production process involved the use of the melt-quenching approach to produce a series of barium borosilicate glasses with the specific chemical formula 55B2O3+(26-x)BaO+12SiO2+7Na2O + xTb4O7, where x = 0, 0.5, 1, 2, and 3 mol%. X-ray diffraction (XRD), Raman spectroscopy, optical absorption, and photoluminescence spectra measurement were used to examine the prepared samples. X-ray diffraction revealed the non-crystalline character of the assembled samples. The Raman spectroscopy revealed that the incorporation of Tb4O7 into borosilicate glasses induced alterations in their structure. As the doping of Tb3+ ions increases, the density and molar volume of the glasses under investigation increase. Furthermore, the ion concentration and field strength increase while the polaron radius and inter-ionic distance decrease. The glass optical absorption spectra showed five peaks in the wavelength range from 300 nm to 2000 nm: 5L10, 5D3, 5D4, 7F(0, 1, 2), and 7F3, attributed to Tb3+ ion electronic transitions. In addition, optical parameters like optical energy gap, Urbach energy, refractive index, molar refractive index, reflection loss, electronic polarizability, and optical transmission coefficient were computed. Terbium-doped borosilicate glasses had a decreased optical energy gap and an improved refractive index. Photoluminescence spectra were excited at 325 nm and showed five peaks in the range of 400–750 nm. Photoluminescence (PL) emission spectra exhibit distinct peaks in the visible range.

Novel Tb3+ doped borophosphate glass scintillator for X-ray imaging

In this study, we introduce an efficient green-emitting material made from Tb3+ doped borophosphate scintillating glass for X-ray imaging. An influence of Tb2O3 concentration on the physical, optical, luminescent, and scintillation properties of glasses were investigated. The glass density and refractive index increase, while the molar volume and Tb3+ inter-ionic distance decreases with Tb2O3 addition. These glasses absorb the photons in range of UV, Vis, and NIR. The excitations by UV and X-ray on glasses causes the strong green emission centered around 545 nm by the 5D4 → 7F5 transition of Tb3+. The energy transfer from Gd3+ to Tb3+ was occurred in this emission. The glass doped with 4 mol% of Tb2O3 demonstrates the highest emission intensity at 545 nm due to the concentration quenching. The decay time of glasses are in few milliseconds. The integral X-ray scintillation efficiency of 4 mol% doped glass is 52% compared to that of BGO crystal. Additionally, this glass was proceeded in the X-ray imaging and yielded the image with satisfied resolution, characteristics and MTF values, compared to that obtained from YAG:Ce crystal. The developed glass has a potential for X-ray imaging applications, especially in the medical imaging, flaw detection, and security inspection.

Equal Rights for Activators – Ytterbium to Terbium Cooperative Sensitization in Molecular Upconversion

AbstractMolecular scaffolds are ideal for investigating upconversion (UC) at the highest spatial resolution and to create precisely controllable luminescent materials. Such control may be the key to overcoming the limitations of brightness and reproducibility found in UC micro‐ and nanoparticles. Cooperative UC can significantly increase luminescence brightness and bulk studies showed that highest efficiencies can be obtained by sensitizer‐to‐activator ion ratios ≥ 2, that is, via high probabilities of sensitizing the emitting lanthanide ion. Using nonanuclear molecular complexes, the authors demonstrate both experimentally and theoretically that interion distances are more relevant and that the highest UC efficiencies are actually attained for sensitizer‐to‐activator ion ratios around 1. By modeling accretive and cooperative sensitization UC, energy migration, and fitting experimental data, it is revealed that cooperative sensitization is predominant for the determination of UC luminescence intensities, whereas energy migration defines UC luminescence kinetics. The implementation of interion distances and different energy transfer mechanisms into advanced modeling of experimental UC data will be paramount for designing brighter and better UC materials.

Physical Properties Study of Sodium Doped Boro-Tellurite (Na<sub>2</sub>O: TeO<sub>2</sub>-B<sub>2</sub>O<sub>3</sub>-ZnO) Glasses

Five boro-tellurite glasses with chemical formula 55TeO2-(12-x)B2O3-32ZnO-(1+x)Na2O (TZBN), (x= 0; 1; 2; 3; 4; mole%) were successfully synthesized by conventional melt-quenching technique. The physical properties of the glass was studied to understand effect of partial substitution between B2O3 and Na2O. The density was measured using pycnometer based on Archimedes law. The other physical properties can be obtained by assisted some mathematical equation. Refer to the measurement, the density was found decreased by 4.905 to 4.590 gr/cm3 because the molecular weight difference between B2O3 and Na2O. Meanwhile the molar volume increased by 25.05 to 27.11 cm3/mole due to higher atomic radii of Na rather than B which raise NBO inside the glass network. Meanwhile, OPD, Vo, polaron radius, inter-ionic distance, packing density,and number of bond per unit volume consequently have been decreased. While the Field strength has increase due to stronger Na-O bonds. Reflects from the results the TZBN glasses could be used as active material for laser.

The effect of nickel additive and ion irradiation on the structural and optical properties of lithium borate glasses

The study investigates the impact of nickel oxide (NiO) doping (0%, 0.1%, 0.2%, and 0.3% wt%) on the glass composition 85B2O3-15Li2O using the melt quenching technique. Both X-ray diffraction (XRD) and FTIR confirm the amorphous nature and functional groups. Density, molar volume, average boron separation, ion concentration, interionic distance, polaron radius,. UV-visible absorption (200–1100 nm) was also recorded before and after nitrogen ion beam irradiation (fluence: 8x1017 and 16x1017 ion/cm2). Results indicate a decrease in the optical energy gap (Eoptical gap) and an increase in Urbach’s energy (EU) with higher NiO content, especially post-irradiation. Nitrogen ion irradiation at higher doses (16x1017 ion/cm2) induces more significant effects, attributed to increased non-bridging oxygen species (NBOs) formation and finally dielectric parameters were measured from 100 Hz to 100 kHz. Overall, the ability to tailor borate glass properties via nitrogen ion irradiation holds promise for diverse technological applications in optoelectronics, photonics, sensors, and radiationdetection

Mechanical and thermal response of XFe2O4 (X = Zn, Ag and Co) spinel ferrites via IR-spectroscopy and first-principles calculations

The lack of comprehensive literature on the all-important aspect of the elasticity of spinel ferrites led to the hydrothermal synthesis of different (Co, Zn, Ag) spinel ferrites. IR spectroscopy revealed the characteristic absorption bands of metal-oxygen in all three compositions. The shifting of tetrahedral and octahedral bending vibrations towards higher frequencies owes to changes in inter-atomic and inter-ionic distances. Elastic parameters, wave velocities, and Debye temperature have been calculated using IR spectroscopy data. Elastic parameters have been higher for Co ferrites than Zn and Ag ferrites. The Poisson ratio seems to be consistent for different spinel ferrites. Shear wave velocity has been found to be higher than longitudinal wave velocity because perpendicular particle vibrations take higher energy than parallel vibrations. Wave velocities have been found to be higher in Ag ferrites than in the other two compositions. Debye temperature follows the same trend as elastic parameters. Additionally, we have confirmed the mechanical stability of the Co, Zn, and Ag ferrites using the first-principles calculations in the density functional theory (DFT) approach framework. Interestingly, the Co/Zn/Ag ferrites exhibit semiconducting nature with a band gap of 3.96/3.66/0.71 ev. Our study could pave the way for next-generation spintronic devices.

Quaternary layered Cr‐doped modified NCMFe cathode material for Lithium‐Ion Batteries

AbstractA series of cathode materials, Li[Ni0.6Co0.12Mn0.2Fe0.08]1‐xCrxO2 (x=0, 0.02, 0.04, 0.06), are synthesized via the co‐precipitation method. Structural characterization shows that Cr3+ ions are successfully incorporated into the material structure and evenly dispersed on the surface of crystal particles with other metal elements. The Cr‐doped material shows a well‐defined hexagonal layered structure with less cation mixing, and the increase in interionic and interlayer distances is beneficial for the transport of lithium ions. Compared to the pure NCMFe phase, the cyclic and rate performances of the Cr‐doped quaternary materials have been significantly improved. Among them, the 4Cr material exhibits the best electrochemical performance. The capacity retention rate after 50 charge‐discharge cycles at 0.1 C was increased from 74.83 % to 87.32 %. The rate performance has also increased from 87.6 % to 92.69 %. The Cr‐doped cathode can reduce the charge transfer resistance and enhance the stability of the layered structure, which results in outstanding electrochemical performance of the Cr‐doped cathode. CV and EIS tests were conducted on materials with various Cr doping levels, further confirming that Cr doping can reduce the degree of polarization in electrode materials, enhance charge and discharge reversibility, and reduce the charge transfer resistance of materials.

Effective Ion Charges in Ion Exchangers and Electrolyte Solutions

Structures, effective numbers of charges and molecular orbitals of ion pairs and representative fragments of a sulfocation exchanger in various ionic forms were calculated by the non-empirical quantum chemical method of LCAO MO. The effective charges of ions in accordance with the principles of the molecular orbital method were fractional values. For contact ion pairs, where the effective ion charges were experimentally measured by X-ray absorption spectroscopy, we obtained full agreement with the calculated values. The charge numbers of cations and anions differed in both hydrate-separated and ion-exchange systems due to the fact that the oxygen atoms of hydrated water molecules influenced the formation of molecular orbitals. According to the obtained values of the numbers of charges and interionic distances, the energies of the electrostatic interaction of ions were calculated using the integral form of Coulomb's law. Experimental values of the energies of chemical bonds of counterions and fixed ions were obtained using the conductometric contact-difference method when measuring the specific electrical conductivity of MK-40 cation exchange membranes in the range of 20-50oC and according to the Arrhenius equation. The coordination of experimental and calculated chemical bond energies in the ion exchanger was achieved after the addition of hydrogen bond energy to the electrostatic interaction energy. In order to be able to completely nonempirically calculate the energies of chemical bonds in an ion exchanger, we took the value of the hydrogen bond energy as the excitation energy of the first energy level of deformation vibrations of water molecules having a value of 19.4 kJ/mol. A comparison of the contribution of the electrostatic interaction to the total binding energy of alkali metal cations with a fixed ion showed its small role in ion exchange and membrane transport, so that in the first approximation we can say that the transfer of alkali metal cations is determined by the breaking of the hydrogen bond. For cations of a larger charge (calcium), the electrostatic energy already makes a significant contribution, and for trivalent ions, the energies of the Coulomb interaction and hydrogen bonding are close to each other. The soliton mechanism of translation of the energy of deformation vibrations along a chain of water molecules is considered, which allows explaining the decrease in energy when several hydrogen bonds are broken.

Electrocaloric, thermal and structural properties of Ba1−xLixTi0.975V0.025O3±δ (0 ≤ x ≤ 0.05) ceramics

The present work reveals the electrocaloric, structural, thermal, and other physical properties of Ba1−xLixTi0.975V0.025O3±δ (0 < x ≤ 0.05) ceramics synthesized via the solid-state chemical reaction method. X-ray studies reveal the presence of BaTiO3 phase in all the samples, wherein the phase fraction of BaTiO3 decreases with increasing Li content. Besides this, the replacement of lighter weight Li-atoms in place of Ba-atoms increases porosity and consequently decreases the density of the samples. However, the molar volume increases while inter-ionic distance decreases due to the small size of Li-atoms as compared with Ba-atoms. In this series, the sample with x = 0.05 exhibited a maximum change in entropy i.e., ΔS = 0.728 JK−1 kg−1 and the largest change in temperature i.e., ΔT = 0.422 K at 90 °C with the application of a 20 kV/cm electric field. Moreover, the x = 0.05 ceramic has the largest value of specific heat i.e., 626.59 JK−1 kg−1 as discovered during DSC investigations. In the present study, Li- and V- are attributing to good sintering and Li- in place of Ba- is enhancing electrocaloric properties in BaTiO3 ceramic.

New analytical results in solid state physics using the Lambert W function

Analytical solutions in physics are always preferred for the sake of mathematical completeness. For this, using the Lambert W function, I derive closed-form analytical expressions for the equilibrium interionic distance in an ionic crystal, the formation energy of a vacancy in a crystal, the zero-temperature energy gap of a clean-limit superconductor and the critical Kosterlitz–Thouless temperature for the phase transition in 2D-XY model. Besides their theoretical interest, some of the present results suggest alternative experimental determinations of the relevant physical quantities. In addition, I similarly derive an explicit analytical formula based on the Lambert W function for a determination of the Boltzmann constant. This formula is proposed here as a theoretical basis for an experimental method to measure this constant. This method is suitable for undergraduate physics students.

Molecular Design of Organic Ionic Plastic Crystals Consisting of Tetracyanoborate with Ultralow Phase Transition Temperature.

Organic ionic plastic crystals (OIPCs) are a ductile soft material where the composing ions are in isotropic free rotation, while their positions are aligned in order. The rotational motion in its plastic phase promotes ion conduction by decreasing the activation energy. Here, we report novel OIPCs comprised of tetracyanoborate ([TCB]-) and various organic cations. In particular, the OIPC composed of [TCB]- and spiro-(1,1')-bipyrrolidinium ([spiropyr]+) cations can transform into its plastic phase at ultralow temperature (Tp = -55 °C) while maintaining a high melting point (Tm = 242 °C). Replacement of the cation with either tetraalkylammonium or phosphonium and comparing their phase behavior, the high Tm was attributed to the relatively small interionic distance between [spiropyr]+ and [TCB]-. At the same time, the low Tp was realized by the restricted vibrational mode of the spirostructure, allowing the initiation of isotropic rotational motion with less thermal energy input.

Physical and Optical Properties of Lead-Tungsten-Tellurite Glasses

By using the melt quenching approach, a number of tellurite-based heavy metal oxide glasses codoped with varied lead oxide (PbO), (80-x)TeO2-20%WO3-xPbO (x = 5, 10, 15 and 20 mol%) compositions, have been created. By using UV-Vis-IR spectroscopy, forbidden energy gap, Urbach energy, and refractive index were calculated and the contribution of PbO to the glasses structure was investigated. Calculations were also made for physical parameters such as density, molar mass, and oxygen packing density, polaron radius, inter-ionic distance, and molar refraction. The direct and indirect optical band gaps is 3.29 to 3.33 eV and 3.2 to 3.3 eV, respectively. The fact that the nonbridging oxygen ion content rises with increasing PbO content and shifts the band edge to lower frequencies, may be the cause of a drop in the values of the energy band gap Eg.

The Role of Stepwise Photoionization in Measurements of the Ionization Potentials in Dense Plasma

The interaction of high-contrast high-intensity laser radiation with solids allows us to create hot or warm plasma of solid or even over-solid density, such as in the case of inertial fusion particularly. The multicharged ions contained in it can no longer be considered isolated. As a result, this leads to a decrease in the ionization potentials and to the disappearance of a number of bound ionic states. To describe the ionization potential depression, two major approaches are now used predominantly, where the key parameter is either average interelectronic or interionic distance. Since neither of the approaches can be substantiated purely theoretically, their applicability can only be established by comparison with experimental results. In recent experiments with X-ray free-electron lasers, it was concluded that the ionization potential depression rather depends on the interelectronic distance. However, when measuring ionization potentials, it was assumed that the main role in ionization processes is played by the direct photoionization of the ion ground state. In the present paper, we show that stepwise photoionization processes should play a significant role in dense plasma, disrupting a straight correspondence between the threshold in direct photoionization by X-ray laser photons and the actual ionization potential of multicharged ions. It means that the measurement results mentioned above are not correct, and the main conclusion about the importance of the interelectronic distance for depression of the ionization potential is not correct.

Structural, physical and optical study of calcium modified bismuth borovanadate glasses: V2O5-B2O3-Bi2O3-CaO

Comprehensive research into quaternary glass systems' structural, physical, and optical characteristics was conducted, specifically for glass series 60V2O5-20B2O3-(20-x)Bi2O3-xCaO, where x = 0-20 mol%. Using X-ray diffraction (XRD), their non-crystalline character was confirmed. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used for morphological study to confirm glass formation. Several techniques were employed to investigate the effects of incorporating CaO on the physical, optical, and structural characteristics of glasses composed of bismuth boro-vanadate. As-prepared glass samples have been analysed to determine how density (ρg), crystalline volume (Vcryst), molar volume (Vm), and oxygen packing density (OPD) changes with composition. Additional determined physical parameters include interionic distance (Ri), Calcium yields field (F), ion concentration of Ca2+ (N), and polaron radius (Rp). DSC thermograms reveal that glass transition temperature (Tg) rises in tandem with the concentration of calcium oxide, demonstrating an improvement in the glass system's thermal stability. FTIR and Raman spectroscopy examination of all glass samples confirmed that V2O5 forms a network with VO5 units. After x = 10 mol%, the proportion of non-bridging oxygens in the glass matrix rises as VO5 units are converted into VO4 units along with the transformation of BO3 units into BO4 units. Bi2O3 is found in glass matrix in BiO6 and BiO3 units. As concentrations of calcium oxide were increased, UV–Visible spectroscopy revealed nonlinear trends in various optical parameters such as optical energy (Eopt), Urbach energy (EU), cut-off wavelength (λC), molar refractivity (RM), metallization criterion, and refractive index (n). The glasses prepared in this study exhibit high-level optical basicity (ranging from 1.164 to 1.238), electronic oxide ion polarizability (3.304–3.869), and metallization criterion (0.249–0.304). These findings point to the possibility that the glasses can be suitable for non-linear optical applications.

Carbonates of alkaline earth metals: Impact of the cation size on strengths of interionic interactions and polymorphic preferences

The energies of all types of pair-wise interionic interactions between atoms of the representative (MCO3)13 clusters sampled from X-ray structures of rhombohedral magnesite (M = Mg) and calcite (M = Ca), on one hand, and orthorhombic aragonite (M = Ca) and cerussite (M = Pb), on the other hand, are evaluated theoretically to ascertain how the size of a divalent metal cation governs the preferable existence of rhombohedral or (and) orthorhombic polymorph (polymorphs) at ambient temperature and pressure. The carbonates studied and their clusters are considered as those consisting of (i) columns of carbonate anions (CAs) separated by trios of cations, (ii) ribbons and layers of CAs, and (iii) rods and layers of cations. For each cluster, coordination energies of six CAs by a cation and six cations by a CA are evaluated. Energies of interactions of C and O atoms of columns and ribbons with cations and energies of inter-anionic C···O, O···O, and C···C interactions in column and ribbons of clusters are compared. Strengths of cation – cation repulsions are also evaluated. Analyses of the interaction energies, interionic distances in the carbonates studied, and thermodynamic properties of carbonates of alkaline earth metals allow one to understand how the size of a particular divalent metal cation affects relative thermodynamic stabilities and the very existence of its rhombohedral or (and) orthorhombic crystalline phase (phases).

Investigations of structural modifications, physical and optical properties of lead boro-tellurite glasses doped with europium trioxide for possible optical switching applications

This manuscript intends to the structural modifications, and physical and optical properties of a set of heavy metal alkali boro-tellurite glasses doped with Eu2O3. These glasses were produced by a conservative melt-quenching method. The existence of non-crystalline properties in the glasses was ascertained by X-ray diffraction analysis. The structural modifications were noticed by MAS-NMR spectroscopic investigation. Physical properties such as density, molar volume, oxygen packing density, average boron-boron separation, interionic distance, and polaron radius have been calculated by a suitable approach. The optical absorption studies were made through UV-visible absorption spectroscopy in the 350 nm to 800 nm wavelength range. The optical properties namely, optical energy bandgap, Urbach energy, optical basicity, electronegativity, and electric susceptibility, were also determined by using appropriate methods. The MAS-NMR spectroscopic experiments reveal that fewer BO4 units are converted to BO3 units and those NBOs are turned into bridging oxygen at a lower rate. The optical refractive index values and optical dielectric constant range from 2.241 to 2.358, and 5.0220 to 5.5601, respectively. The obtained energy band gap values (Eg(d): 3.367 eV to 3.597 eV and Eg(ind) 2.109 eV to 2.863 eV) and other significant optical parameters suggest that the investigated glasses are potential candidates for europium-doped fiber amplifier applications and possible optical switching applications.

Grain boundary segregation of nickel vacancies and space charge zone formation in NiO through interactions among Ni2+, O2−, and Ni3+

Defects like nickel vacancies (VNi″), holes (Ni3+) with different segregation tendencies to grain boundary (GB) can govern the properties of nickel oxide (NiO) – a promising material for energy applications. An atomistic model of non-stoichiometric NiO bicrystal with θ°001100 GB is developed to understand the segregation of VNi″, Ni3+ to GB from various ionic interactions. According to the model lattice positions available for VNi″ in GB possess lower attractive (from Ni2+-O2− interactions) and higher repulsive (from Ni2+-Ni2+ interactions) energies when compared with those in grain interior. This is due to the differences in these inter-ionic distances in GB and grain interior. Hence VNi″ segregate to GB. Contrarily, grain interior is more favorable for formation of Ni3+ in GB. These Ni3+ form a space charge zone adjacent to the GB. The model helps in understanding VNi″ segregation to GB and space charge zone formation.

On a shape of band-to-acceptor luminescence line in semiconductors

A theoretical explanation is proposed for the shape of the long-wavelength edge of the luminescence line, which is caused by the recombination of a free electron and a hole of a neutral acceptor. The formation of complexes, in which a single hole is localized by the field of two attracting ions (\(A_{2}^{ - }\) complexes) and the subsequent recombination of holes in such complexes with electrons of the conduction band are considered. The Coulomb repulsion in the final state after recombination and the dispersion of the complexes in terms of the interionic distance provide an extended long-wavelength tail of the luminescence line, comparable in magnitude to the ionization energy of a single acceptor.