Covalency Parameters Research Articles

Covalency parameters for nine-coordinated thorium acylpyrazolone complexes along with their synthesis and crystal features

This study discusses the synthesis and characterization of three thorium complexes with a general composition of [Th(L)4(EtOH)] demonstrated a nine-coordinated geometry in acylpyrazolone chemistry, a novel finding supported by single crystal evidence. A detailed analysis of complex [Th(L2)2(DMF)] was conducted, utilizing single-crystal X-ray diffraction data and Hirshfeld surface area analysis to investigate secondary interactions, exploring the planarity and bonding characteristics of the crystals. Covalency parameters such as the Nephelauxetic ratio, Sinha parameter, bonding parameter, and angular overlap parameter were calculated from electronic spectral data, revealing positive covalency and electron delocalization across the 5f orbital for all complexes. Notably, the presence of solvent bound to the 9th coordination site of the complex suggests potential changes in covalency across different solvents, thereby indirectly impacting chemical characteristics.

Gamma-irradiated fluorophosphate glasses doped with various transition metals: A spectroscopic study

The 20NaF–60P2O5–20Na2O fluorophosphate glass systems doped with 3 wt% of CoO and NiO were manufactured using traditional melting techniques. Optical parameters were investigated for the studied composites before and after irradiation by 20 kGy of gamma rays. For the studied composites, the presence of defects within the glass network can explain the decrease of the Urbach energy (Eu) due to gamma irradiation or the increase in it due to the addition of the transition metals (nickel oxide and cobalt oxide) to the base composite. After gamma irradiation, a red shift was seen in the spectrum of the dissipation factor (tan δ). According to the calculated values of volume energy loss function (VELF), and surface energy loss function (SELF), the energy lost at the surface of the composites under investigation is larger than the energy lost within the composites' constituent materials. All investigated composites demonstrated an insulating property by obtaining the values of the covalency parameter (M) less than unity. All of the nonlinear optical parameters were increased after irradiation of the studied composites, whereas the highest values were recorded for the irradiated composite doped by CoO. Following the intrinsic and extrinsic defects produced by the former oxide itself and by added modified oxide dopants inside the glassy network was important to explain changes inside the network by ESR spectra for prepared fluorophosphate composites. Moreover; defects induced inside the glass network by 20 kGy of γ-ray have been followed to continue the ongoing study of the nature of the prepared glassy network.

Neodymium based acylpyrazolone complexes: Synthesis and physicochemical characterizations

The electronic spectra of three neodymium acylpyrazolone complexes with the compositions [Nd(DMBPMP)3(H2O)(EtOH)] (Nd1), [Nd(DMMCPMP)3(H2O)(EtOH)] (Nd2), and [Nd(DMBPTMP)3(H2O)(EtOH)] (Nd3) have been analyzed. Utilizing ESI-mass, FT-IR, thermogravimetric, and single crystal X-ray diffraction methods, the structure of the DMBPTMP ligand and all three complexes were investigated. According to the single crystal analysis of Nd2, the complex is mononuclear and eight-coordinate (NdO8) with a distorted square antiprismatic geometry. A powder XRD pattern confirmed a similar structural arrangement of the other two complexes. The transition 4G5/2 ← 4I9/2, which is close to the centre of the visible spectrum (∼17,500 cm−1), exhibits hypersensitivity, which stands out in stark contrast to the behaviour of many other typically weak and reliably unchanging, typical 4f-4f transitions. Through a comparative analysis of calculated oscillator strength, Judd-Ofelt parameters, and covalency parameters in various solvents, hypersensitivity, symmetry characteristics, and covalency have been thoroughly investigated. The promotion of 4f-4f electric-dipole intensity has been found to be particularly successful with DMF, DMSO, pyridine and ethanol. Utilizing Judd-Ofelt parameter Ω4 values and Hirshfeld analysis, long-range secondary π⋯π stacking or H-bonding interactions were investigated. Using solid-state emission spectra, intensity of emission spectra and antenna effect energy diagram was examined.

Structural Features, Emission Analysis, and Covalency Comparison of Neodymium Acylpyrazolone Complexes using Oscillator Strengths, Covalency and Judd‐Ofelt Parameters**

AbstractThree distorted square antiprismatic eight coordinated neodymium acylpyrazolone complexes were synthesized having the compositions [Nd(L1)3(H2O)(EtOH)] (NdL1), [Nd(L2)3(H2O)(EtOH)] (NdL2), and [Nd(L3)3(H2O)(EtOH)] (NdL3). The structure of all three complexes was examined using ESI‐mass, FT‐IR, and thermogravimetric methods. According to the single crystal analysis of NdL1, the complex was found eight‐coordinated (NdO8) with a distorted square antiprismatic geometry. A powder XRD pattern confirmed a similar structural arrangement of the other two complexes. In electronic absorption spectra, the transition 4G5/2←4I9/2, which is close to the centre of the visible spectrum (~17,500 cm−1), exhibits hypersensitivity, which stands out in stark contrast to the behaviour of many other typically weak and reliably unchanging, typical 4f–4f transitions. Through a comparative analysis of calculated oscillator strength, Judd‐Ofelt parameters, root mean square deviation, radiative lifetime and covalency parameters in various solvents, hypersensitivity, symmetry characteristics, and covalency have been thoroughly investigated. The promotion of 4f–4f electric‐dipole intensity has been found to be particularly successful with ethanol, pyridine, DMF, and DMSO. Utilizing Judd‐Ofelt Ω4 values and Hirshfeld analysis, long‐range secondary π⋅⋅⋅π stacking or H‐bonding interactions were investigated. The intensity of emission spectra, quantum yield, stokes shift, and antenna effect energy diagram was examined using solid‐state emission spectra.

Uranyl(VI) Mixed-ligand complex synthesis and characterization using 4-acylhydrazone-5-pyrazolone and 4-acylpyrazolone: Covalency, crystal assay, DFT study and Hirshfeld analysis

Newly prepared bidentate HLA and tridentate Bz-HLA ligands were used to synthesize the novel uranyl mixed ligand [UO2(HLA)(Bz-HLA)] complex with pentagonal bipyramidal geometry. HLA ligand was prepared via the common acylation method, and the Bz-HLA ligand was prepared using the Schiff base reaction of HLA with a benzohydrazide molecule. FTIR, 1H and 13C NMR, SCXRD, molar conductance, and TG-DTA were mainly implemented to examine the structure of produced compounds. The combined covalency effect of complex due to both ligands has been studied, which was discovered to be influenced by the average bond length values on the pentagonal plane, uranyl axial bond lengths, ligand coordination, and donor ability of various atoms. To demonstrate that solvents have no impact on the covalency of the synthesised complex, Sinha's covalency parameters were computed using UV–vis data. DFT calculations were performed in order to validate experimental findings in comparison to theoretical findings, and theoretical bond characteristics were also investigated through the recognition of global index values. Hirshfeld surface analysis was used to examine the crystal strength, energy characteristics and non-covalent surface interactions. Analysis using cyclic voltammetry(CV) shows that the complex is irreversibly reducing. Understanding the Schiff base of acylpyrazolones and their covalency in uranyl complexes allow for the investigation of a wide range of chemical properties and applications.

Synthesis, covalency parameters, energy calculations and crystal features of acylpyrazolone derived pentavalent Uranyl complex along with DFT and Hirshfeld analysis

A σ-donating acylpyrazolone DMBPMP (4-(3,5-dimethyl benzoyl) 1-phenyl 3-methyl 5-pyrazolone) ligand and its Uranyl acylpyrazolone complex [UO2(DMBPMP)2(EtOH)] were synthesized to analyze the nature of covalency, reactivity, and redox properties. The structure, pentavalent bipyramidal geometry, and complex composition are mainly scrutinized through their single-crystal x-ray crystal data, molar conductivity, gravimetric estimation, FTIR significant vibrations, δ-values of 1H NMR, 13C NMR and TG-DTA plots. The covalency of the Uranyl complex mainly depends on average bond length values on the pentagonal equatorial plane, Uranyl axial bond lengths, stretching frequency values, coordinated solvent on the fifth coordination site, and different aryl group substitution on the first position of the pyrazolone ring; and it can be confirmed through FTIR, single-crystal, and electronic UV–Vis spectral characterization methods. The UV–Vis data was also valuable for identifying n → π*, π → π*, and LMCT transitions and calculating Sinha’s covalency parameters, which shows that the complex can show maximum covalent character in DMSO solvent and covalency decreases in DMSO > DMF > Ethyl acetate > Ethanol > CHCl3 order. DFT calculations were performed to get an excellent correlation and comparison with all experimental values. This correlation and comparision is helpful to identify global index parameters to get an idea of the physical as well as chemical properties of such systems and to confirm the characteristics theoretically by HOMO-LUMO energy gap, theoretical vibrations, natural electronic configuration, and NBO charges. The Hirshfeld surface analysis was also carried out to identify the crystal strength through interaction energies and energy frameworks in the ligand and intermolecular non-covalent surface interactions with fingerprint plot details in both ligand and complex. Electro-chemical analysis in CV-DPV plots provides information on the redox properties of uranyl moiety.

A theoretical study of concentration-dependent xCaF2-20TeO2-(79‒x)Na2B4O7-CuO glass: Local distortions, EPR parameters and optical properties

The electron paramagnetic resonance parameters (EPR) and local structure properties of the Cu2+ center in xCaF2–20TeO2-(79-x)Na2B4O7-CuO glasses are theoretically studied based on the high-order perturbation formulae of a 3d9 ion in a tetragonally elongated octahedron. Determined from the best fitted piecewise linear function (the reverse point at 40 mol%), the corresponding overall varying tendencies and fluctuations of local distortions, EPR parameters and optical properties are reproduced, which can be ascribed to the generated non-bridging oxygen's. The microscopic mechanisms of the above concentration dependences for these quantities are illustrated from the transformation of BO3 and TeO3 units. Meanwhile, the electronic properties are obtained through the covalence parameters N and the decrease optical basicity, which both mean the decreasing covalency of the whole glass systems and strong ionicity around Cu2+.

Synthesis, Covalency Parameters, Energy Calculations and Crystal Features of Acyl Pyrazolone Derived Pentavalent Uranyl Complex Along with Dft and Hirshfeld Analysis

Synthesis, Covalency Parameters, Energy Calculations and Crystal Features of Acyl Pyrazolone Derived Pentavalent Uranyl Complex Along with Dft and Hirshfeld Analysis

Comparative 4f-4f Spectral Analysis of Simultaneous Complexation of Pr(III) with L-Tryptophan in Presence and Absence of Ca2+ and Zn2+ Ions in Aqueous Medium: Energy, Intensity and Kinetic Studies

The spectral analysis of the complexation of praseodymium (Pr3+) with L-tryptophan in various aqueous solvent applying a quantitative probe of 4f-4f transition spectra. The study is carried out by calculating various energy interaction parameters such as the nephelauxetic effect (β), percent covalency (δ), bonding parameter (b1/2), Slater-Condon (Fk) and intensity parameters like oscillator strength (P) and intensity of Judd-Ofelt parameters Tλ (λ = 2, 4, 6). The paramagnetic behaviour of Pr3+ shows 3H4→1D2, 3H4→3P0, 3H4→3P1, 3H4→3P2 types of specific 4f-4f absorption bands and are observed at the visible reason of 427-610 nm. The intensities of 4f-4f transition bands rise on the addition of Ca2+ and Zn2+ ions toward the complexation of praseodymium (Pr3+):Try and extended result in the case of Ca2+ ion compared to the Zn2+ ion due to increase in the interaction between ligand and 4f orbital of metal ions. These bands on immediate minor’s coordination change around praseodymium (Pr3+) found to be highly sensitive due to the formation of heterobimetallic complex between L-tryptophan (Try) with Pr3+ in the existence of Zn2+ and Ca2+ ions. The complexation of Try with Pr3+ in the presence of Zn2+ and Ca2+ ions are monitors simultaneously from the sensitivity of the bands using energy parameters and oscillator strength. The rate of heterobimetallic complexation of both Zn2+ and Ca2+ ions was calculated from the 4f-4f transition at different temperatures. The thermodynamic parameters and activation energy calculated from the rate constants from different temperatures are more favourable in case of Try form complex with Pr3+ in the presence of Ca2+ ion as compared to Zn2+ ion.

Experimental and Computational Study of a Tetraazamacrocycle Bis(aryloxide) Uranyl Complex and of the Analogues {E═U═NR}2+ (E = O and NR).

The reaction of [U(κ6-{(t-Bu2ArO)2Me2-cyclam})I][I] (H2{(t-Bu2ArO)2Me2-cyclam} = 1,8-bis(2-hydroxy-3,5-di-tert-butyl)-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane) with 2 equiv of NaNO2 in acetonitrile results in the isolation of the uranyl complex [UO2{(t-Bu2ArO)2Me2-cyclam}] (3) in 31% yield, which was fully characterized, including by single-crystal X-ray diffraction. Density functional theory (DFT) computations were performed to evaluate and compare the level of covalency within the U═E bonds in 3 and in the analogous trans-bis(imido) [U(κ4-{(t-Bu2ArO)2Me2-cyclam})(NPh)2] (1) and trans-oxido-imido [U(κ4-{(t-Bu2ArO)2Me2-cyclam})(O)(NPh)] (2) complexes. Natural bond orbital (NBO) analysis allowed us to determine the mixing covalency parameter λ, showing that in 2, where both U-Ooxido and U-Nimido bonds are present, the U-Nimido bond registers more covalency with regard to 1, and the opposite is seen for U-Ooxido with respect to 3. However, the covalency driven by orbital overlap in the U-Nimido bond is slightly higher in 1 than in 2. The 15N-labeled complexes [U(κ4-{(t-Bu2ArO)2Me2-cyclam})(15NPh)2] (1-15N) and [U(κ4-{(t-Bu2ArO)2Me2-cyclam})(O)(15NPh)] (2-15N) were prepared and analyzed by solution 15N NMR spectroscopy. The calculated and experimental 15N chemical shifts are in good agreement, displaying the same trend of δN (1-15N) > δN (2-15N) and reveal that the 15N chemical shift may serve as a probe for the covalency of the U═NR bond.

Topological analysis and glass kinetics of Se-Te-Ag lone pair semiconductors

The physical properties of Ag doped Se based ternary glassy alloys have been examined theoretically. (Se 70 Te 30 )100−x Ag x (0.0 ≤ x ≤ 8.0) chalcogenide alloys have been prepared by quenching method. The results show that the system is in floppy mode having constant average coordination number 2. The estimated density shows an increase with the Ag content. The mean bond energy and glass transition temperature vary in a similar fashion with an increment in Ag atomic % in the Se-Te system. The value of cohesive energy (1.91 eV mol−1 to 1.97 eV mol−1) and average bond strength (24.19 kcal mol−1 to 25 kcal mol−1) has shown increasing trend in the system. From the results of the investigated samples, the covalency parameter > 90%. So, it can be assumed that compositions are stable glass formers and may be used in the infrared system.

Covalency and Racah parameters of Fe3+ in Mn–Zn–Cr nanoferrites

This study presents the covalency and Racah parameter (B) of Fe3+ in Mn–Zn–Cr nanoferrites, which prepared by citrate–nitrate combustion method. Racah parameter was determined from the spectral data. The bands in the range of interest in optical absorbance are wide and asymmetric; a deconvolution (deconvolution to their component bands) of the experimental spectra becomes compulsory. Further, these spectra were employed to obtain Racah parameter. Racah parameter was decreased, with further Fe addition, from 540 to 441 cm-1. Also, nephelauxetic ratio (β) was decreased from 0.532 to 0.435. This denotes that the bonds of Fe3+ and its surroundings become more covalent (the covalency is increased).

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF HETEROMETALLIC COMPLEXES OF Pr(III) WITH Zn(II), CO(II) BASED ON ETHYLENEDIAMINETETRAACETIC AND ETHYLENEDIAMINEDISUCCINIC ACIDS

New heterometallic f-d-complexes of Pr (III), Co(II), Zn(II) with aminopolycarboxylic acids (ethylenediaminetetraacetic, ethylenediaminedisuccinic acids) have been synthesized and spectroscopically characterized. It was found that complexes with a molar ratio of Pr:M3d: EDTA=1:2:2 are formed for ethylenediaminetetraacetic compounds, and that in the case of complexes based on EDDS, heteronuclear compounds of the equimolar composition Pr: M3d: EDDS = 1: 1: 1 are formed. It is shown that it is expedient to carry out the synthesis of heterometallic complexes on the basis of mono­nuclear polycarboxylates of 3d metals, which act as a «building block» for the preparation of a heterobinuclear compound by the exo coordination of additional metal ions. The complexes are characterized by the method of electron absorption spectroscopy. It is shown that independent of 3d-metal, for both heterometallic systems based on EDDS, a hypsochromic shift of the absorption maxima relative to νmax is observed for the homonuclear praseodymium complex. For ethylenediaminetetraacetate systems, the absorption maxima undergo both low- and high-frequency shift, which indicates the different nature of the ligand field effect, which is caused primarily by differences in the structure of the corresponding heteronuclearaminopolycarboxylates due to the presence of a chiral carbon atom in the EDDS molecule. For the supersensitive transitions Pr(III)) 3H4 →3P2 and 3H4 → 1D2 , the covalence parameters of the Ln-O bond have been calculated: osci­llator power (P), nepheloxetic parameter (β), covalence parameter (b1/2), Sinha parameter (δ). Analysis of the spectroscopic parameters indicates a decrease in the covalence of the lanthanide-ligand bond in the transition from mono- to heteronuclear complex, and a decrease in the local symmetry of the lanthanide ion occurs in the order Ln (III) aqua ion <hete­rometallic complex <monometallic complex. Heteronuclear complexes are several orders of magnitude more stable than mononuclear ones due to the formation of additional bonds or metallacycles with donor ligand atoms. It is noted that the stability of complexes with EDDS is lower than that of the corresponding complexes with EDTA due to the different size and number of chelated metallacycles. The obtained heteronuclear complexes belong to folded complexes, in which the ligand-complexone realizes the maximum denticity to the lanthanide ion, and the coordination sphere of the 3d-cation is formed by carboxyl groups EDTA / EDDS and inner-sphere water molecules. In this case, the ions of 3d-metals are in a distorted octahedral environment, and the coordination number of Pr(III) is 8.

Synthesis and theoretical characterization of ternary Cux(Ge30Se70)100−x glasses

The Cux(Ge30Se70)100−x (0 ≤ x ≤ 12 at.%) chalcogenide alloys have been synthesized by the conventional melt quenching technique. The physical properties such as the mean coordination number, density, molar volume, compactness, overall bond energy, and cohesive energy were estimated for the Cu doped Ge-Se glassy alloys. The chemical bond approach (CBA) was used to predict the type and proportion of the formed bonds in the studied glasses. Subsequently, 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 2.6 to 2.77. The density and glass compactness show an increase with the Cu content, whereas the main atomic volume decreases. The cohesive energy and the heat of atomization show a similar behavior trend with the enhancement of Cu % in the Ge-Se binary glasses. The optical band gap was estimated theoretically compared with the previously published experimental values for the Cux(Ge30Se70)100−x (0 ≤ x ≤ 12 at.%) thin films. The covalency parameter >91% for the studied glasses so that the compositions may be used as a stable glass former. Furthermore, the mechanical properties as the elastic bulk modulus, Poisson’s ratio, Young’s modulus, micro-hardness, and Debye temperature were investigated as a function of the Cu content.

Computation of energy interaction and intensity parameters for the complexation of Pr(III) with glutathione at different pH in the presence/absence of Mg2+: 4f-4f transition spectra as a probe

Free and complexed Pr3+ ion with reduced glutathione (GSH) have been studied in DMF and acetonitrile medium at different pH values (2, 4 and 6) in the presence and absence of Mg2+ ions through FTIR, comparative absorption spectroscopic analysis involving 4f-4f transition spectra. The interaction between the metal and ligand has been analyzed based on the computed values of different parameters, such as the Slater-Condon (Fk) parameter, Racah (Ek) factor, Lande (ξ4f) parameter, Nephelauxetic effect (β), bonding parameter (b1/2) percent covalency parameter (δ), oscillator strength (P) and Judd-Ofelt parameters (Tλ, λ = 2,4,6).

Neodymium (III) and erbium (III) complexes with new unsaturated β-diketones

In this work, the new coordination compounds of Nd(III) and Er (III) with b-diketonate ligands containing an unsaturated substituent at the a-position of the chelate ring (dimethylheptendione and dimethyloctendione) were synthesized. The composition and structure of the synthesized compounds were studied using physicochemical methods of analysis such as the elemental, NMR, IR and electron spectroscopy and thermogravimetric analysis. Using IR spectroscopy, it was established that ligands are bidentate-cyclically coordinated to metals. The results of thermogravimetric analysis indicate that the complexes are nonvolatile and decompose to oxides of the corresponding metals, and their coordination sphere is supplemented with water molecules. From the shape and position of the bands in the electronic absorption spectra and diffuse reflection spectra, it was determined that for the complexes Ln (b-dik)3.nH2O (Ln =Nd, Er, b-dik = dmhpd, dmod, n = 2-3) the tetragonal symmetry of the nearest coordination environment; coordination polyhedron is a square antiprism. When comparing the diffuse reflectance spectra of dimethylheptendionate and dimethyloktendionate complexes among themselves and with the previously studied complexes with methacrylacetophenone, it was noted that the shape of the spectra and the spectral splitting of the bands for the corresponding metals are not significantly different. This allows to conclude, that the coordination environment of the studied b-diketonate compounds is close.Based on the band shifts in the electronic spectra, the covalence parameters of the Ln–O bond and the oscillator strength were calculated, from which it was also shown that the nature of the substituent affects the covalence parameters, but does not affect the symmetry and structure of the coordination polyhedron. Based on the studies conducted, the monomeric structure of the synthesized complexes was definitely confirmed. Accordingly, they can be used in further work as monomers in polymerization reactions and the preparation of precursors of luminescent materials.

Defining of the Covalence Parameters in Cs2NaYCl6:Eu3+ and Cs2NaEuCl6 by the Optical Spectra

Defining of the Covalence Parameters in Cs₂NaYCl₆:Eu³⁺ and Cs₂NaEuCl₆ by the Optical Spectra

Spectroscopic investigations on La3+, Pr3+, Nd3+ and Gd3+ complexes with a multidentate ligating system: Luminescence properties and biological activities

A series of eight complexes of Ln chlorides and perchlorates (Ln = La3+, Pr3+, Nd3+ and Gd3+) with the ligand, L2− (H2L = 2,2′-iminobis [N-(3-hydroxypropyl)acetamide]), are prepared and characterized by spectral (FTIR, FAB mass, and UV–Visible, 1D and 2D NMR), thermal, electrochemical and density functional theory (DFT) studies. The analytical and spectral data confirmed the composition to be [LnLCl(H2O)2]·2H2O {La3+(1), Pr3+(2), Nd3+(3) and Gd3+(4)} and [LnLClO4(H2O)2]·H2O {La3+(5), Pr3+(6), Nd3+(7) and Gd3+(8)}. The spectral data ascertained a hepta-coordinate geometry of the complexes, which was further supported from DFT studies. Analytical and thermal data supported the stoichiometry of the complexes. The oscillator strengths and the covalency parameters (β, b1/2 and δ) were evaluated from electronic (UV–Vis) spectral studies. The complexes exhibited moderate emission in the luminescence spectra of Pr3+ and Nd3+. Cyclic voltammetric studies confirm the formation of quasi-reversible (PrIII/IV and GdIII/IV) redox couples in solution. Complexes and the free ligand were tested for antibacterial and antifungal properties. Molecular docking results ascertain the comparable binding affinity of the neutral ligand (H2L), complex (4) and complex (8) with B-DNA.

Computation of Energy, Intensity and Thermodynamic Parameters for the Interaction of Ln(III) with Nucleic Acid: Analysis of Structural Conformations, Chemical Kinetics and Thermodynamic Behaviour through 4f-4f Transition Spectra as Probe

Nucleosides and Nucleotides are polydentate ligands, offering potential binding sites for metal ions. Energy interaction parameters: Slater Condon Fk (cm-1), Spin Orbit interaction ξ4f (cm-1), Nephelauxetic Ratio (β), Bonding (b1/2) and Covalency (δ) parameter for the interaction of Pr(III) with Nucleoside and Nucleotide are evaluated to study the mode of binding of the Nucleic Acid Components (Guanosine and Guanosine Triphosphate) with Pr(III). Further Intensity Parameters like Oscillation Strength and Judd Ofelt Parameter (T2, T4, T6) have been evaluated to investigate degree of inner or outer sphere co-ordination of Pr(III) with Nucliec Acid ligands. Comperative Absorption Spectra in different solvents substantiate the informations, gathered from the evaluated values of both energy interaction and intensity parameters. Further evaluation of Thermodynamic parameters (ΔG, ΔH and ΔS) through Kinetic studies enable to provide the detailed information about the reaction pathways and thermodynamic behavour of the complexation process of neucleosides and nucleotides with Pr(III) and Ca2+.

Ho3+-Yb3+ codoped tellurite based glasses in visible lasers and optical devices: Judd-Ofelt analysis and frequency upconversion

The optical absorption and frequency upconversion emission in the Ho3+/Yb3+ codoped TeO2-ZnO (TZ), TeO2-ZnO-WO3 (TZW) and TeO2-ZnO-WO3-TiO2 (TZWTi) glasses prepared by melting and quenching method has been studied. Judd-Ofelt theory has been used to calculate the Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6), transition probabilities, radiative lifetimes, absorption cross sections and the branching ratios. Upconversion (UC) emission bands centered at ∼ 549 nm, ∼658 nm and ∼754 nm are observed upon 980 nm excitation. On codoping with the Yb3+ ions at 3.0 mol% the upconversion emission intensity enhancement of about ∼57 times, ∼342 times and ∼480 times for the green band whereas for the red band arising from the Ho3+ ions it is about ∼71 times, ∼438 times and ∼707 times respectively have been observed. The enhancement observed in the UC emission intensity is explained on the basis of efficient energy transfer from Yb3+ to Ho3+, larger absorption cross section, larger oscillator strengths and increase in the local field corrections factor. The spectroscopic quality factor Ω4/Ω6 has been calculated to get the information about the developed materials for laser applications. The upconversion emission cross section determined on the basis of Judd-Ofelt analysis is found to be maximum for Ho-Yb-TZWTi glass. The nephelauxetic ratio, bonding and covalency parameters have been calculated to know the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The high color purity 83.8% has been reported in the codoped glasses at ∼81.2 W/cm2 pump power density.