Degree Of Covalency Research Articles

Enhanced luminescence properties and Judd-Ofelt analysis of novel red emitting Sr2LiScB4O10: Eu3+ phosphors for WLED applications

In this work, a new series of red emitting Eu 3+ ions activated Sr 2 LiScB 4 O 10 phosphors were synthesized by a traditional high temperature solid-state reaction technique and their structural and luminescence behavior were studied through analyzing X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy, optical absorption, photoluminescence as well as decay spectral measurements, respectively. XRD pattern showed that the prepared Sr 2 LiScB 4 O 10 :Eu 3+ phosphors crystallized into monoclinic system with the space group of P2 1 /n. FTIR study revealed the presence of different stretching and bending vibrational bands of borate group. Bonding parameter values which obtained from the band positions of the absorption spectra revealed the covalent character which existing between the Eu 3+ ions and its surrounding ligands. Under 395 nm excitation source, the studied phosphors exhibit intense red emissions in the 617 nm wavelength region corresponding to the 5 D 0 → 7 F 2 transition of Eu 3+ ions. Judd-Ofelt (JO) intensity parameters were evaluated from the PL emission spectra in order to facilitate a study of the nature of site symmetry. From the CIE color chromaticity analysis it is evident that the prepared phosphors are found to emit an intense red light with the reasonable color coordinate and color purity under the excitation of blue light and the same may be suggested as an appropriate red component for developing white LEDs. The important radiative parameters were obtained for the emission transitions using JO intensity parameters in order to ensure the suitability of prepared phosphors for display devices and laser applications. • Eu 3+ : Sr 2 LiScB 4 O 10 phosphors were fabricated by solid state reaction method for display device applications. • Eu 3+ activated Sr 2 LiScB 4 O 10 phosphors exhibited red luminescence which was confirmed by CIE chromaticity diagram. • Higher and increasing Ω 2 values contribute to the higher degree of covalency between Eu–O bond. • Bright red light with color purity of 94% was attained in the prepared phosphors excited by 395 nm. • 0.6EuSLSB phosphor exhibit appreciable radiative properties suitable for red laser and white LEDs.

Frontispiece: Covalency in Actinide Compounds

This frontispiece illustrates two ways of achieving a higher degree of covalency in actinide compounds, one employs orbital energy degeneracy and the other—orbital overlap between the 5f and ligand orbitals. For more information see the Concept article by V. V. Klepov, H.-C. zur Loye et al. on page 5835.

Nature of the Hydrogen Bond Enhanced Halogen Bond.

The factors responsible for the enhancement of the halogen bond by an adjacent hydrogen bond have been quantitatively explored by means of state-of-the-art computational methods. It is found that the strength of a halogen bond is enhanced by ca. 3 kcal/mol when the halogen donor simultaneously operates as a halogen bond donor and a hydrogen bond acceptor. This enhancement is the result of both stronger electrostatic and orbital interactions between the XB donor and the XB acceptor, which indicates a significant degree of covalency in these halogen bonds. In addition, the halogen bond strength can be easily tuned by modifying the electron density of the aryl group of the XB donor as well as the acidity of the hydrogen atoms responsible for the hydrogen bond.

Physical and mechanical properties of ternary Ge-Se-Sb glasses for near-infrared applications

Many physical properties such as the average coordination number (CN), the compactness (δ), the overall bond energy (〈E〉), the cohesive energy (CE), the mean bond energy (E s), and the overall electronegativity difference (Δχ) as well as the degrees of ionicity (Ion) and covalency (Cov) were estimated theoretically. The chemical bond approach (CBA) was used to predict the type and proportion of the formed bonds in the studied glasses. Consequently, several structural and physical properties have been estimated. The results show that the studied glasses are rigidly connected, having an average coordination number increase from 2.41 to 2.61. Two approaches have been successfully used to estimate the band gap (E g) theoretically compared with the previously published experimental values for the Ge18Se82−xSbx (5 ≤ x ≤ 25 at. %) glasses. Values of E g decrease from 1.59 to 1.15 eV by an increase of the Sb content from 5 to 25 at. %. i.e. the wavelengths corresponding to E g values lie in the near-infrared range of spectra, which make these glasses candidates for the near-infrared applications. Furthermore, the ultrasonic longitudinal (v L ) and shear wave (v T ) velocities propagating through the glasses have been used to estimate the mechanical parameters such as the elastic bulk modulus, Poisson’s ratio, Young’s modulus, micro-hardness, and temperature of Debye. It was found that a change in slope occurs for various physical, mechanical, and structural properties near the stoichiometric composition (x ≈ 18 at. %) at which the glass structure consists of heteropolar bonds only.

DFT calculations and experimental studies of the electronic structure and optical properties of Tl4PbI6

We present data of an experimental and theoretical study of the electronic band structure of ternary thallium lead iodide, Tl4PbI6. The XPS studies yield high quality of the Tl4PbI6 crystal, its low hygroscopicity, high stability regarding Ar+-ion-irradiation and comparatively strong degrees of covalency of the chemical Tl–I and Pb–I bonds. The latter peculiarity of the crystal under study is confirmed by first-principles calculations that are made within density functional theory (DFT). In the present DFT calculations we consider different models for exchange-correlation potential, and found that the best agreement between experiment and theory is observed when we use modified Becke-Johnson potential as elaborated by Tran-Blaha and involve also the Hubbard correcting parameter U and spin-orbit coupling (SOC) effect (the so-called TB-mBJ + U + SOC model). Employing the TB-mBJ + U + SOC calculations, we examine in detail partial and projected densities of states as well as band dispersions. The TB-mBJ + U + SOC calculations indicate that Tl4PbI6 is a direct gap semiconductor with the energy band gap value of 2.347 eV. This theoretical value is in excellent agreement with that evidenced from experimental measurements of spectral allocation of the absorption coefficient in the range of the fundamental absorption edge yielding Eg = 2.35 eV at room temperature. The present measurements of the second harmonic generation intensity of the Tl4PbI6 crystal feature high prospective of its application in NLO devices for the studied range of the fundamental beam, approximately 1 μm. We have established that the ignoring of the SOC effect in the calculations predicts a nondirect semiconductor nature in Tl4PbI6 being in conflict with the experiment. Based on the TB-mBJ + U + SOC model, we have calculated in detail the main optical constants of Tl4PbI6 allowing to draw a conclusion that it is a good semiconductor for application in optoelectronic devices.

The role of covalent bonding and anionic redox for the performance of sodium cobaltate electrode materials

It is common belief that conventional layered oxide battery cathode materials operate on a cationic redox mechanism, and that oxygen oxidation triggered by charge compensation results in oxygen loss and limited practical capacity. In this work, thin films of sodium cobaltate demonstrate a mixed redox behavior with strong oxygen participation well within the reversible intercalation range. This unexpected behavior is attributed to an increasing degree of covalency of the transition metal-oxygen (TM-O) bonds during deintercalation in combination with a high structural flexibility of the material. These insights are based on electronic structure data obtained using an operando solid state cell, allowing analysis with unpreceded control, and are supported by density functional theory (DFT) calculations. They demonstrate that the spectrum of possible charge compensation mechanisms is broader than commonly believed, and indicate that tuning TM-O covalency is a key factor for increasing the capacity also of conventional layered materials.

Comprehensive Bonding Analysis of Tetravalent f-Element Complexes of the Type [M(salen)2

Key questions for the study of chemical bonding in actinide compounds are the degree of covalency that can be realized in the bonds to different donor atoms and the relative participation of 5f and 6d orbitals. A manifold of theoretical approaches is available to address these questions, but hitherto no comprehensive assessments are available. Here, we present an in-depth analysis of the metal-ligand bond in a series of actinide metal-organic compounds of the [M(salen)2] type (M = Ce, Th, Pa, U, Np, Pu) with the Schiff base N,N'-bis(salicylidene)ethylenediamine (salen). All compounds except the Pa complex (only included in the calculations) have been synthesized and characterized experimentally. The experimental data are then used as a basis to quantify the covalency of bonds to both N- and O-donor atoms using simple electron-density differences and the quantum theory of atoms in molecules (QTAIM) with interacting quantum atoms. In addition, the orbital origin of any covalent contributions was studied via natural population analysis (NPA). The results clearly show that the bond to the hard, charged O-donor atoms of salen is consistently not only stronger but also more covalent than bonds to the softer N-donor atoms. On the other hand, in a comparison of the metals, Th shows the most ionic bond character even compared to its 4f analogue Ce. A maximum of the covalency is found for Pa or Np by their absolute and relative covalent bond energies, respectively. This trend also correlates with a significant f- and d-orbital occupation for Pa and Np. These results underline that only a comprehensive computational approach is capable of fully characterizing the covalency in actinide complexes.

Structures, energies, and bonding in the microsolvation of Na+

A stochastic search of the potential energy surfaces for the interctions between the sodium cation and up to six explicit water molecules was performed under Møller–Plesset second–order perturbation theory (MP2) with extended basis sets. At these low molecularties, the sodium cation is more likely to occupy the interior of the cluster, energetically favoring a maximum coordination number of four, even when five or six water molecules are available. An energy decomposition analysis reveals a major contribution from electrostatic interactions to cluster stabilization, with non-negligigle induction contributions accounting for ≈20% of the total interaction. Topological analysis of the electron distribution unambiguously describe H2O⋯Na+ ionic interactions. Hydrogen bond networks seem to arrange in order to maximize the stability of Na+ via a clear charge transfer pattern, where electron density is withdrawn from the O–H bonds towards Na+. Because of this reorganization of the electron density, and because of the perturbative effect of the formal charge, all H2O⋯H2O hydrogen bonds are also highly ionic in nature with some degree of covalency.

Phosphate-modified Co-Ni phosphide heterostructure formed by interfacial and electronic tuning for boosted faradaic properties.

Rational structural and compositional modulation endows electrode materials with unique physicochemical characteristics due to their adjustable electronic properties. Herein, a phosphate-modified hierarchical nanoarray consisting of a heterojunction with a well-aligned cobalt phosphide nanowire core and nickel phosphide nanosheet shell on flexible carbon cloth (denoted as CoP@Ni2P-CC) is engineered. The phosphate-modulated heterogeneous phosphide with a tuned electronic structure, additional heterojunction interfaces, and high degree of covalency in the chemical bonds accelerates the reaction kinetics and enhances the energy storage performance. Due to these reasons, the as-obtained phosphide-based heterostructured CoP@Ni2P-CC electrode delivers a capacity of 475.9 C g-1 at 0.5 A g-1 with a satisfying rate capability, which is greatly superior to that of its transition metal counterparts (sulfide, selenide, and oxide). After being assembled into a flexible hybrid supercapacitor (FHSC), a wide operating voltage (1.8 V), high energy/power densities (49.8 W h kg-1/8.6 kW kg-1), and long-term stability (85.1% capacity retention after 10 000 cycles) were achieved. This work may provide a general method from multiple strategies for designing reliable pseudocapacitive materials for flexible electronics.

Influence of Se doping on recently synthesized NaInS2-xSex solid solutions for potential thermo-mechanical applications studied via first-principles method

In the present work, the structural and hitherto unexplored thermal and mechanical properties of NaInS2-xSex (x = 0, 0.5, 1.0, 1.5 and 2.0) compounds have been studied using the density functional theory. Besides, the elastic anisotropy indices and hardnesses of NaInS2-xSex have been investigated as Se content is varied. The mechanical stability of all the compounds under study has been confirmed. The ratio of shear to bulk modulus (G/B) is low suggesting that the NaInS2-xSex (x = 0.5 and 1.5) compounds exhibit damage tolerant (ductility) properties while rest of the compositions are brittle in nature. The predicted hardness (H) values are also influenced with the Se content in the following order: H (NaInSSe) >H (NaInS2) >H (NaInSe2) >H (NaInS1.5Se0.5) >H (NaInS0.5Se1.5). All the anisotropic indices under study indicate that NaInS2-xSex compounds are anisotropic in nature. The Mulliken bond population analysis suggests that the degree of covalency of In-S/Se bonds decreases when S is substituted by Se. The origin of low Debye temperature (ΘD) and low minimum thermal conductivity (Kmin) have been successfully explained by considering the mean atomic weight (M/n) and average bond strength of the compounds. Temperature dependence of heat capacities (Cv, Cp) and linear thermal expansion coefficient (α) are also estimated using the quasi-harmonic Debye model and discussed. The low values of Kmin, ΘD and α and damage tolerant behavior clearly indicate that the NaInS2-xSex (x = 0.5 and 1.5) compounds can be used as promising thermal barrier coating materials for high temperature applications.

METAVALENT CHEMICAL COMPOUNDS OF THE TYPE AIBVCVI2 (AI – Li, Na, K, Rb, Cs; BV – As, Sb, Bi; CVI – Se, Te)

The concept of chemical bonding is one of the key concepts in the modern chemical science. The main types of chemical bonds traditionally distinguished in the scientific literature are ionic, covalent and metallic; whereas hydrogen bonds and intermolecular interaction forces are usually taken as secondary bonds. It should be noted, however, that there are no sharp boundaries for the above types of chemical bonds.In order to predict the type of chemical bond between atomic particles, a special atomic property called the electronegativity [i.e. the ability of a given atom in a molecule to attract electron density (or valent electrons)] is widely used. The concept of electronegativity and the first scale of electronegativities of chemical elements were proposed by L. Pauling in 1932; later, several alternative scales of electronegativities were developed, including those by Mulliken and by Allred–Rochow.Using the difference between the electronegativities of atoms (DEN) and the sum of the electronegativities of atoms (SEN), one can obtain quantitative parameters which characterize the chemical bonds in specific compounds. In particular, the difference in the electronegativities of the A and B atoms characterizes the degree of ionicity for the A–B bond, while the sum of electronegativities indicates either the degree of covalency (at relatively large SEN values) or the degree of metallicity (at low SEN values). The sum of electronegativities can be replaced, if necessary, by the average electronegativity (ENav.) of the compound. Taking the elementary substances Cs and F2 and the binary compound CsF as reference points in the coordinates ENav.–DEN, a diagram triangle was constructed, which conveniently and clearly illustrates the type of chemical bond of different chemical compounds.The analysis of the ternary chalcogenide AIBVCVI2 (AI – Li, Na, K, Rb, Cs; BV – As, Sb, Bi; CVI – Se, Te) compounds (which have been studied for a long time by the researchers of the Uzhhorod National University) by using the aforementioned diagram triangle in the coordinates ENav.–DEN has revealed the fact that the considered compounds are characterized by the combined (so-called "metavalent") chemical bonding recently identified in the specialized scientific literature as a separate bonding type.

Effect of W‒O bonding on gas sensitivity of nanocrystalline Bi2WO6 and WO3

It is known that adsorptive capacity and surface reactivity of metal oxides depends on chemical composition, which influences the characteristics of metal‒oxygen bonds, e.g. degree of covalency, effective atomic charges, bond energy and bond length. Tungsten oxide and bismuth tungstate have perovskite-related structures and close semiconductor properties, but different chemical composition. The presence of bismuth in Bi2WO6 results in distinct W‒O bond length and bond energy, respective to WO3, which may be one of the factors controlling the surface reactivity, as well as the occurrence of bismuth-related surface sites. Tungsten oxide is a renowned material for heterogeneous catalysts, photocatalysts, and sensors. Bismuth tungstate has been extensively studied as a photocatalytic material, and an interest in sensor applications of this compound emerged recently. Yet, there is a lack of comparative and systematic studies of the electronic structure and sensing properties of tungsten oxide and bismuth tungstate. Such a study would be promising for the elucidation of the role of W‒O bonds in controlling the sensing behavior to different analyte gases. In this work, the comparative study of electronic and sensing properties of Bi2WO6 and WO3 was performed. Band structures, charge distribution and metal-oxygen bonds energies were calculated by first principles quantum chemical approach. Nanocrystalline Bi2WO6, WO3 and composite Bi2WO6 + WO3 were synthesized. Bismuth tungstate showed an improved sensitivity to volatile organic compounds (ethanol, formaldehyde, acetone, benzene) and poor sensitivity to nitrogen dioxide, in contrast to WO3. Based on the experimental and computational data, the effects of W‒O bond energy and charge distribution on the sensitivity to target gases of bismuth tungstate and tungsten oxide were rationalized.

Topological Analysis of Hydroxyquinoline Derivatives Interacting with Aluminum Cations or with an Al(111) Surface

The reactivity of hydroxyquinoline derivatives (native molecules (Hq) and modified species (HqX, X = Br, SO3H, or SO3-)) is investigated either (i) with aluminum cations for the formation of chelates or (ii) with aluminum surfaces for their adsorption properties, in the framework of the dispersion-corrected Density Functional Theory (DFT-D). It is shown that the substituent X has no influence on the complexation to the aluminum cation of the deprotonated active form, i.e., the one exhibiting a phenolate moiety and referred to as q- for the native Hq and qXn- (n = 1 or 2) for its derivatives. The formation energies of the Alq3 and Al(qX)3 complexes, taking values of -60.87 ± 3.10 eV in vacuum and -24.30 ± 0.29 eV in water, are indicative of a strong chelating affinity of the q- and qXn- (n = 1 or 2) anions for the aluminum cations. ELF and QTAIM topological analyses on these complexes evidence that the bonding of the deprotonated species with the Al3+ ion is ionic with a very weak covalence degree. The para or ortho substituent X of the phenolate moiety of the qXn- (n = 1 or 2) derivatives modifies the electronic structure only locally and thus does not influence their O- or N-coordinating properties. The adsorption properties of the latter on an Al(111) surface have also been studied within periodic DFT-D calculations. The adsorbed species are strongly interacting with the Al(111) surface, as shown by the value of the adsorption energy of -3.69 ± 0.21 eV for the most stable geometries. Various adsorption modes of the q- and qXn- (n = 1 or 2) derivatives are characterized on the Al surface, depending on stabilizing or destabilizing interactions with the substituents X. On the basis of QTAIM descriptors, the bonding of the hydroxyquinoline species on the aluminum surface is characterized as ionic with a weak covalent character.

Bonding Trends in Tetravalent Th-Pu Monosalen Complexes.

The synthesis of three complex series of the form [AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N‐donor molecules. Structure determination by single‐crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An−Cl and An−N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An−O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An−N and An−Cl bonds, as well as the highest degree of covalency of the An−O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties.

Structural Characteristics and Microwave Dielectric Properties of CaW1−x(Mo1/2Te1/2)xO4 (0.01 ≤ x ≤ 0.17) Ceramics with (Mo1/2Te1/2)6+ Substitution

Microwave dielectric properties of CaW1−x(Mo1/2Te1/2)xO4 (0.01 ≤ x ≤ 0.17) ceramics with (Mo1/2Te1/2)6+ substitution were investigated. For the specimens sintered at 825–950 °C for 3 h, a single phase of a scheelite structure was observed up to x = 0.13, while secondary phases were detected above x = 0.17. The relative densities of the specimens were higher than 95%, and the grain morphologies were uniform and clean for the entire range of compositions. The quality factor (Qf) depended on the intrinsic factors such as the W-site bond characteristics of CaWO4 evaluated by the bond valence and degree of covalency, and confirmed by the full width at half maximum of the internal mode peak of Raman spectroscopy. However, Qf was also affected by the extrinsic factors, such as the formation of the secondary phases, which showed the maximum Qf value (167,800 GHz) at x = 0.13 and then decreased. The dielectric constant (K) increased with (Mo1/2Te1/2)6+ substitution, which was affected by the dielectric polarizabilities of constituent ions. As the (Mo1/2Te1/2)6+ content increased, the temperature coefficient of resonant frequency (TCF) decreased, which was associated with an increase of oxygen bond valence.

The X-ray constrained wavefunction of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex: a theoretical and experimental study of dihalogen bonds and other noncovalent interactions.

The synthesis and X-ray structure determination of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex (1) are described. The C-Br...Br dihalogen bond present in 1 has been characterized by means of topological studies of the electron density. Both the quantum theory of atoms in molecules and the electron localization function approaches have been applied to several theoretically calculated wavefunctions as well as to an X-ray constrained wavefunction. In addition, a number of theoretical techniques, such as the source function, the reduced density gradient method and the interacting quantum atoms approach, among others, have been used to analyse the dihalogen bond as well as several intramolecular interactions of the type C-H...Br-C which have also been detected in 1. The results show clearly that while bonding in the latter interactions are dominated by electrostatic components, the former has a high degree of covalency.

Tris[N,N-bis-(3,5-di-tert-butyl-benz-yl)di-thio-carbamato-κ2 S,S']-μ3-sulfido-tris-μ2-disulfido-triangulo-trimolybdenum(IV) iodide.

The title compound, [Mo3(C31H46NS2)3S7]I, crystallizes on a threefold rotational axis in P31c (space group No. 159). The [Mo3S7(S2CN(CH2C6H3-3,5- t Bu2)2)3]+ cations are arrayed in sheets in the ab plane with inter-ligand hydro-phobic inter-actions between tert-butyl groups guiding the packing arrangement. These cations form stacks parallel to the c axis with a separating distance of 10.9815 (6) Å (the c axis length) between the Mo3 centroids. On the underside of the cluster, opposite the μ3-S2- ligand, the iodide counteranion forms close contacts of 3.166 (2) Å with the sulfur atoms of the μ2-S2 2- ligands. These contacts are less than the sum of the van der Waals radii of the atoms (1.8 and 2.1 Å for S and I, respectively), thus indicating an appreciable degree of covalency to the [Mo3S7(S2CN(CH2C6H3-3,5- t Bu2)2)3]+⋯I- inter-actions.

Compression of curium pyrrolidine-dithiocarbamate enhances covalency.

Curium is unique in the actinide series because its half-filled 5f 7 shell has lower energy than other 5f n configurations, rendering it both redox-inactive and resistant to forming chemical bonds that engage the 5f shell1-3. This is even more pronounced in gadolinium, curium's lanthanide analogue, owing to the contraction of the 4f orbitals with respect to the 5f orbitals4. However, at high pressures metallic curium undergoes a transition from localized to itinerant 5f electrons5. This transition is accompanied by a crystal structure dictated by the magnetic interactions between curium atoms5,6. Therefore, the question arises of whether the frontier metal orbitals in curium(III)-ligand interactions can also be modified by applying pressure, and thus be induced to form metal-ligand bonds with a degree of covalency. Here we report experimental and computational evidence for changes in the relative roles of the 5f/6d orbitals in curium-sulfur bonds in [Cm(pydtc)4]- (pydtc,pyrrolidinedithiocarbamate) at high pressures (up to 11 gigapascals). We compare these results to the spectra of [Nd(pydtc)4]- and of a Cm(III) mellitate that possesses only curium-oxygen bonds. Compared with the changes observed in the [Cm(pydtc)4]- spectra, we observe smaller changes in the f-f transitions in the [Nd(pydtc)4]- absorption spectrum and in the f-f emission spectrum of the Cm(III) mellitate upon pressurization, which are related to the smaller perturbation of the nature of their bonds. These results reveal that the metal orbital contributions to the curium-sulfur bonds are considerably enhanced at high pressures and that the 5f orbital involvement doubles between 0 and 11 gigapascal. Our work implies that covalency in actinides is complex even when dealing with the same ion, but it could guide the selection of ligands to study the effect of pressure on actinide compounds.

Microstructural comparison between PMMA-SiO2 and PMMA-TiO2 hybrid systems using Eu3+ as ion-probe luminescence

Organic-inorganic Eu3+-doped PMMA-SiO2 and PMMA-TiO2 hybrid systems were synthesized by sol-gel. The doping ions were used as ion-probe luminescence to analyze the differences in the microstructure of the hybrid matrices. The local symmetry environment of the Eu3+ ions in the hybrid matrices was described by the asymmetry parameter (R), defined as the intensity ratio of the 5D0 → 7F2/5D0 → 7F1 transitions. The photoluminescence of PMMA-SiO2 with quenched emission and lower R is consistent with a symmetric, hydrated environment surrounding the Eu3+ ions. Meanwhile, the higher value of R and the higher emission intensity, observed for PMMA-TiO2, reveal a lower symmetric environment of the Eu3+ ions. Furthermore, the emission and excitation bands of the 5D0−7F0 transition shows a red shift in the PMMA-TiO2 spectra, indicating higher Eu-O covalence degree. The calculated values of the Judd-Ofelt parameters are in agreement with the higher Eu-O covalence degree in this hybrid material.

Judd−Ofelt calculations for spectroscopic characteristics of Dy3+-activated strontium magnesium borate glass

Some new type of strontium magnesium borate glass system doped with Dy3+ (various contents 0.1, 0.3, 0.5, 0.7 and 1.0 mol%) were produced using the conventional melt-quenching. Obtained glasses were thermally stable, highly transparent, and moisture resistant. As-prepared samples were characterized to determine their spectroscopic traits. The Judd-Ofelt (J-O) intensity Ωλ (λ = 2, 4, 6) and radiative parameters were calculated to validate the experimental results on the optical characteristics. The XRD pattern of the as-quenched samples verified their glassy nature, FESEM images showed uniform textures and EDX analyses detected the presence of appropriate constituents in the host matrix. Glass containing 0.7 mol% of Dy3+ revealed the optimum optical traits where the luminescence emission intensity was attenuated beyond this content. The optical gain for two intense emission transitions (4F9/2→6H15/2 and 4F9/2→6H13/2) was evaluated. The values of Ωλ (λ = 2, 4, 6) determined the ionic nature of the bonding and symmetry environment of the Dy―ligand matrix based on the viscosity and rigidity of the host glass. The 6H15/2→6F11/2 transition was hypersensitive. The ratio of the yellow to blue (Y/B) emission intensity less than unity indicated the lower degree of covalence between Dy3+ and O2− ions thereby makes these glasses effective for the near UV―LEDs. The higher values of the branching ratio (≥ 50 %) and stimulated emission cross-section enabled the proposed glass composition potential for the optical amplifiers and fibres fabrication. The resonant energy transfer and cross-relaxation processes in the Dy3+ were attributed to be responsible for the improved optical features.