Ions In Octahedral Symmetry Research Articles

Spectral studies on Mn 2+ ions doped in sodium–lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption, and luminescence spectral studies of Mn 2+ ions doped in (30− x) (NaPO 3) 6+30PbO+40B 2O 3+ xMnO 2 ( x=1.0, 2.0, 3.0, 4.0, and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g value at g eff≈2.02 with six line hyperfine structure. A weak resonance signal with effective g value at g eff ≈4.3 is also observed for higher concentrations of Mn 2+ ions. The EPR spectra of x =3.0 mol% of Mn 2+ in sodium–lead borophosphate glass sample have been studied at various temperatures. It is observed that the resonance signal intensity decreases with increase in temperature. The optical absorption spectrum exhibits bands characteristic of Mn 2+ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibits single broad band in the green region.

Spectral studies on Cr 3+ ions doped in sodium–lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and emission spectra of Cr 3+ ions doped in (30− x) (NaPO 3) 6+30PbO+40B 2O 3+ xCr 2O 3 ( x=0.5, 2.0, 3.0, 4.0 and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g values at g≈4.55 and g≈1.97. The EPR spectra of x=3.0 mol% of Cr 2O 3 in sodium–lead borophosphate glass sample were studied at various temperatures (295–123 K). The intensity of the resonance signals increases with decrease in temperature. The optical absorption spectrum exhibits four bands characteristic of Cr 3+ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibit one broad band characteristic of Cr 3+ ions in octahedral symmetry. This band has been assigned to the transition 4T 2g (F)→ 4A 2g (F). Correlating EPR and optical data, the molecular bonding coefficient ( α) has been evaluated.

EPR and photoluminescence properties of combustion-synthesized ZnAl2O4:Cr3+ phosphors

An efficient red emitting ZnAl2O4:Cr3+ powder phosphor material was prepared at furnace temperatures as low as 500 °C by using the combustion method. The prepared powders were analyzed by X-ray diffraction and scanning electron microscopy techniques. The optical properties were studied using photoluminescence technique. The EPR spectra exhibit an intense resonance signal at g = 3.74 which is attributed to Cr3+–Cr3+ pairs, and the weak resonance signal of at g = 1.97 is attributed to Cr3+ single ion transition. The spin population (N) has been evaluated as a function of temperature. The excitation spectrum exhibits two broad bands in the visible region which are characteristic of Cr3+ ions in octahedral symmetry and the emission spectrum exhibits zero-phonon line frequencies along with vibronic frequencies. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.

EPR and optical absorption studies of Fe 3+ ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe 3+ ions doped sodium borophosphate glasses (NaH 2PO 4–B 2O 3–Fe 2O 3). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe 3+ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe 3+ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123–295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility ( χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature ( θ p ) have been evaluated from the 1/ χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe 3+ ions in octahedral symmetry. The crystal field parameter ( Dq) and the Racah interelectronic repulsion parameters ( B and C) have also been evaluated and discussed.

EPR, optical, photoluminescence studies of Cr 3+ ions in Li 2O–Cs 2O–B 2O 3 glasses – An evidence of mixed alkali effect

This paper reports the results on mixed alkali effect (MAE) in xLi 2O–(30– x)Cs 2O–69.25B 2O 3 (5 ⩽ x ⩽ 25) glasses doped with 0.75 mol% of Cr 3+ ions studied by Electron Paramagnetic Resonance (EPR), optical absorption and luminescence techniques. The EPR spectra exhibit two resonance signals with effective g values at g ≈ 4.82 and g ≈ 1.99. These two resonance signals are attributed to isolated Cr 3+ ions and exchange coupled Cr 3+ pairs respectively. In addition to this, two more resonance signals with effective g values at g ≈ 4.12 and g ≈ 1.97 are also observed. The resonance signal at g ≈ 4.12 is due to Fe 3+ ions impurity and the resonance signal at g ≈ 1.97 is due to Cr 5+ ions. The population of spin levels ( N) for the resonance signal at g ≈ 1.99 has been calculated at room temperature. It is interesting to observe that N exhibits a non-linear behavior with change in composition showing the mixed alkali effect. The magnetic susceptibility ( χ) was calculated from the EPR data at various temperatures. The exchange coupling constant J between Cr 3+ ions is calculated from relative intensities of g ≈ 1.99 resonance line. The optical absorption spectrum exhibits three bands characteristic of Cr 3+ ions in octahedral symmetry. From the optical absorption spectral data, the crystal field (Dq) and Racah parameters ( B and C) have been evaluated. From ultraviolet absorption edges, the optical band gap and Urbach energies have been calculated. The luminescence spectrum exhibits a red emission peak observed at 640 nm which is assigned to a transition 2 E g → 4 A 2g of Cr 3+ ions.

EPR, optical absorption and photoluminescence properties of Cr 3+ ions in lithium borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence studies of Cr 3+ ions in lithium borophosphate glasses have been studied. The EPR spectra exhibit two resonance signals with effective g values at g = 4.56 and g = 1.96. These resonance signals are attributed to isolated Cr 3+ ions and exchange coupled Cr 3+ pairs, respectively. The EPR spectra have also been studied at various low temperatures. The population of spin levels ( N) participating at resonance signal g = 1.96 has been calculated as a function of temperature. The spin-population ( N) is found to be increasing with decrease in temperature. The magnetic susceptibility ( χ) was calculated from the EPR data. It is observed that as temperature decreases, χ increases in accordance with Curie–Weiss law. The exchange coupling constant J between Cr 3+ ions is calculated from the relative intensities of g = 1.96 resonance line at various temperatures. The optical absorption spectrum exhibits four bands characteristic of Cr 3+ ions in octahedral symmetry. From the optical absorption spectral data, the crystal field (Dq) and Racah parameters ( B and C) have been evaluated. The luminescence spectrum exhibits a red emission peak, which is assigned to a transition from the upper 4T 2g (F) → 4A 2g (F) ground state of Cr 3+ ions. The optical band gap is evaluated from the ultraviolet absorption edges.

EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses

Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 ≤ x ≤ 15 mol%. The EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.

Electron paramagnetic resonance studies on clinochlore from Longitudinal Valley area, northeastern Taiwan

A natural sample of clinochlore from the Longitudinal Valley area of northeastern Taiwan has been characterized by using the powder X-ray diffraction (XRD), differential thermal analysis and electron paramagnetic resonance (EPR) spectroscopic techniques. The lattice parameters of the monoclinic (IIb) clinochlore with the composition (Mg2.988 Al1.196 Fe1.6845 Mn0.026)5.8945 (Si2.559 Al1.441)4 O10 (OH)8 have been calculated from the powder XRD data and are found to be a = 5.347 A, b = 9.223 A, c = 14.250 A, β = 97.2° and Z = 2. The thermal behaviour of the sample showed the typical behaviour of clinochlore with a hydroxyl content of 12.5 wt%. The EPR spectrum at room temperature exhibits two resonance signals centred at g ≈ 2.0 and g ≈ 8.0. The signal at g ≈ 2.0 shows a six-line hyperfine structure which is a characteristic of Mn2+ ions in octahedral symmetry. The resonance signal at g ≈ 8.0 is a characteristic of Fe3+ ions. The EPR spectra have also been recorded at different temperatures (123–295 K). The population of spin levels (N) has been calculated for g ≈ 2.0 and g ≈ 8.0 resonance signals. It is observed that N increases with decreasing temperature. From EPR spectra, the spin-Hamiltonian parameters have been evaluated. The zero-field splitting parameter (D) is found to be temperature dependent. The peak-to-peak width of the g ≈ 8.0 resonance signal is found to increase with decrease in temperature.

Studies on red-emitting Cr 3+ doped barium aluminate phosphor obtained by combustion process

Red-emitting BaAl 2O 4:Cr 3+ phosphor material is prepared by urea combustion route in 5 min. Powder X-ray (XRD) diffraction, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area measurements are used to characterize the as-prepared combustion products. Electron Paramagnetic Resonance (EPR) studies have been carried out on Cr 3+ ions in BaAl 2O 4 phosphors at room temperature and at 110 K. The number of spins participating in resonance ( N) and its paramagnetic susceptibilities ( χ) have also been evaluated. The excitation spectra shows two broad and intense bands corresponding to Cr 3+ ion in octahedral symmetry. The red emission peak observed at 705 nm is identified as due to 2E g → 4A 2g transition from Cr 3+ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr 3+ ion in this phosphor is attributed to a distorted octahedron.

Photoluminescence and EPR studies of Cr-doped hibonite (CaAl 12O 19) phosphors

CaAl 12O 19:Cr powder phosphors have been prepared at 500 °C in less than 5 min by a combustion method and characterized by XRD, FT-IR, SEM, EPR and photoluminescence techniques. The g values evaluated from EPR spectroscopy indicate that the site symmetry around Cr 3+ ions is distorted octahedral as Cr 3+ ions substitute for Al 3+ sites. The number of spins ( N) participating in the resonance for g = 1.97 is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility ( χ) is calculated from the EPR data at various temperatures. From the plot 1/ χ versus T, the Curie constant ( C) and Curie paramagnetic temperature ( θ P) have been evaluated. The exchange coupling constant J between Cr 3+ ions has also been evaluated. The excitation spectrum exhibits two broad bands characteristic of Cr 3+ ions in octahedral symmetry. The crystal field and Racah parameters have been evaluated and discussed.

THE STUDY OF COPPER-DOPED B2O3·Bi2O3 GLASS MATRIX BY SPECTROSCOPIC METHODS

Glasses of x CuO · (100-x)[ B 2 O 3 · Bi 2 O 3] systems with 0≤x≤50 mol% were prepared and investigated by means of FT-IR, Raman and optical absorption spectroscopies. Complex network structures mainly built by BiO 3, BiO 6, BO 3 and BO 4 units were revealed for these glasses by means of FT-IR measurements. Similar structures were evidenced by means of Raman spectroscopy and additional new structural groups were detected in the glass structures, i.e. pyroborate, chain and ring type metaborate groups. The influence of copper-ion content (x) on the short-range order structure evolution was investigated. The optical absorption spectra for all glass samples present a single asymmetric band which corresponds to a 2 B 1g→2 B 2g transition of the of Cu 2+ ions in octahedral symmetry with an elongated tetragonal distortion.

Mixed alkali effect in Li 2O–Na 2O–B 2O 3 glasses containing Fe 2O 3—An EPR and optical absorption study

This paper reports the interesting results on mixed alkali effect (MAE) in xLi 2O–(30- x)Na 2O–69.5B 2O 3 (5 ≤ x ≤ 28) glasses containing Fe 2O 3 studied by electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra in these glasses exhibit three resonance signals at g = 7.60, 4.20 and 2.02. The resonance signal at g = 7.60 has been attributed to Fe 3+ ions in axial symmetry sites whereas the resonance signal at g = 4.20 is due to isolated Fe 3+ ions in rhombic symmetry site. The resonance signal at g = 2.02 is due to Fe 3+ ions coupled by exchange interaction. It is interesting to observe that the number of spins participating in resonance ( N) and its paramagnetic susceptibility ( χ) exhibits the mixed alkali effect with composition. The present study also gives an indication that the size of alkali ions we choose in mixed alkali glasses is also an important contributing factor in showing the mixed alkali effect. It is observed that the variation of N with temperature obeys Boltzmann law. A linear relationship is observed between 1/ χ and T in accordance with Curie–Weiss law. The paramagnetic Curie temperature ( θ p) is negative for the investigated sample, which suggests that the iron ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. The optical absorption spectra exhibit only one weak band corresponding to the transition 6A 1g(S) → 4A 1g(G); 4E g(G) at 446 nm which is a characteristic of Fe 3+ ions in octahedral symmetry.

Theoretical Study of the Spin Hamiltonian Parameters of Vanadium Ions V2+ in CsMgX3 (X = Cl, Br, I)

The spin Hamiltonian g factors and the hyperfine structure constants for V2+ in CsMgX3 (X = Cl, Br, I) are theoretically studied by using the perturbation formulas of these parameters for a 3d3 ion in octahedral symmetry, based on the cluster approach. In such formulas, the contributions from the s-orbitals of the ligands were usually neglected. Here they are taken into account. The theoretical results (particularly the g factor for CsMgI3) show a significant improvement compared with those in absence of the ligand s-orbital contributions in the previous studies.

Spectroscopic investigations of Mn2+ ions doped polyvinylalcohol films

Electron paramagnetic resonance (EPR), luminescence and infrared spectral studies have been carried out on Mn2+ ions doped in polyvinylalcohol (PVA) films. The EPR spectra at room temperature exhibit sextet hyperfine structure (HFS), centered at geff≈2.0 characteristic of Mn2+ ions in octahedral symmetry. The zero-field splitting parameter (D) at room temperature has been evaluated from the intensities of allowed hyperfine lines. The EPR spectra exhibit a marked concentration dependence. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy (Ea) is calculated. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures. From the plot of 1/χ versus T, the Curie constant and Curie temperature have been evaluated. The emission spectrum of Mn2+ ions doped PVA film exhibits three bands centered at 390, 448 and 465 nm. The band at 448 nm is attributed to 4T1g→6A1g transition of Mn2+ ions. The bands at 390 and 465 nm are attributed to the recombination of free charge carriers. The excitation spectrum exhibits two bands at 250 and 216 nm, which are attributed to host lattice absorption bands. The FT-IR spectrum exhibits few bands, which are attributed to O–H, C–H, CC and C–O groups of stretching and bending vibrations.

A new layered organically templated iron(II) phosphite, (C 2H 10N 2)[Fe 3(HPO 3) 4]. Hydrothermal synthesis, crystal structure and spectroscopic and magnetic properties

The (C 2H 10N 2)[Fe 3(HPO 3) 4] compound has been synthesized by using mild hydrothermal conditions under autogeneous pressure and the ethylenediamine molecule as templating agent. The compound crystallizes in the triclinic P 1 ̄ space group with unit-cell parameters a=5.416(1), b=5.416(1), c=13.977(2) Å, α=80.64(2), β=85.25(1), γ=60.03(1)° and Z=1. The final R-factors were R 1=0.053 [w R 2=0.092]. The crystal structure is constructed of layers stacked along the c-axis. The sheets contain FeO 6 octahedra linked by (HPO 3) 2− phosphite oxoanions to give rise to Fe 3O 12 trimeric units sharing faces. The IR spectrum shows the characteristic bands of the phosphite and ethylenediammonium ions. From the diffuse reflectance spectrum, the Dq parameter of 805 cm −1 has been calculated for the iron(II) cation in slightly distorted octahedral geometry. The Mössbauer spectrum exhibits two doublets characteristic of two crystallographically independent iron(II) ions in octahedral symmetry. Magnetic measurements indicate the existence of antiferromagnetic interactions.

A Study of Electron Paramagnetic Resonance and Optical Absorption Spectra of VO2+ Ions in Alkali Barium Phosphate Glasses

The electron paramagnetic resonance and optical absorption spectra of VO 2+ ions in different alkali barium phosphate glasses have been studied and the results have been analysed using C4v symmetry. The EPR spectrum shows eight hyperfine lines characteristic of VO 2+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters, Fermi contact interaction parameter k, dipolar hyperfine coupling parameter P have been evaluated. The EPR spectra exhibit a marked concentration dependence. The EPR spectra were also recorded at different temperatures. The number of spins participating in resonance is found to be increasing with decreasing temperature. The paramagnetic susceptibility χ is calculated from the EPR data. As the temperature decreases, χ increases in accordance with Curie's law. The optical absorption spectrum exhibits two bands corresponding to the transitions 2B2g → 2B1g and 2B2g → 2Eg , characteristic of VO 2+ ions in octahedral symmetry with tetragonal distortion. From the ultraviolet edges of these optical absorption spectra, the optical band gap energies (Eopt) of the glass samples have been calculated. The optical band gap energy varies with alkali content. By correlating EPR and optical absorption data, the molecular orbital coefficients have been evaluated. The theoretical values of optical basicity of the glasses have also been evaluated.

EPR AND OPTICAL ABSORPTION STUDIES OF Mn2+ IONS IN ALKALI BOROTELLURITE GLASSES

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in alkali borotellurite glass systems have been studied. The EPR spectra of all the glass samples exhibit three resonance signals at g ≈ 2.0, g ≈ 3.3 and g ≈ 4.3. A six line hyperfine structure has also been observed at g ≈ 2.0. The concentration and temperature dependence of EPR signals were studied for Mn2+ ions in potassium borotellurite glass samples. The zero-field splitting parameter D has been calculated for different alkali borotellurite glass samples from the intensities of the allowed hyperfine lines. The paramagnetic susceptibility was calculated from the EPR data at various temperatures and the Curie constant was calculated from the 1/χ versus T graph. The optical absorption spectrum exhibits a single broad band near 498 nm and this has been attributed to the spin-allowed 5Eg → 5T2g transition of Mn3+ ions in octahedral symmetry. The optical band gap energy (E opt ) and Urbach energy (Δ E) were calculated from their ultraviolet edges. The optical band gap energy varies between 3.38 and 3.61 eV and increases from Li to K glasses.

Characterisation by EPR spectroscopy

The fresh and used EUROCAT II V 2O 5–WO 3/TiO 2 catalysts have been studied by electron paramagnetic resonance. For both samples, V 4+ in clusterlike arrangement and two sites corresponding to VO 2+ ions in octahedral symmetry axially distorted were found. It has been shown that the TiO 2 phase transformation (anatase → rutile) occurs at lower temperature (1073 K) for the EUROCAT II catalysts than the WO 3/TiO 2 support. Impurities of Fe 3+ ions were detected both on the catalysts and on the WO 3/TiO 2 support. Q-band measurements have allowed a difference in the environment of the Fe 3+ ions caused by the SCR process to be observed. Finally, traces of Ti 3+ ions in the anatase phase have been detected.

Luminescence of In+ in Ce3+ and Tb3+-doped elpasolite-type fluoroindates

This work deals with the identification of In+ ions in octahedral symmetry and the study of their optical properties in crystalline Rb2KInF6:Ce3+ and Rb2KInF6:Tb3+. The presence of In+ ions in the sites of In3+ has been confirmed exciting the Ce3+-doped sample at 41 600 and 32 360 cm−1 and exciting the Tb3+-doped sample at 41 600 cm−1. An hypothesis based on the In3+–Ce3+ and In3+–Tb3+ redox couples for the Ce3+- and Tb3+-doped elpasolite-type fluoroindates has been proposed in order to explain the presence of In+ at the mentioned excitation energies. This redox process is more efficient for the In3+–Ce3+ couple than for the In3+–Tb3+ one. Emission spectra and luminescence decays of In+ have been investigated at 5–300 K in both samples under the above mentioned excitations. Our experimental results have been compared to those obtained for In+-type ions as In+, Ga+, and Tl+ in alkali halides in literature. The transitions between the 5s5p excited configuration and the 5s2 configuration of In+ ions modified by the elpasolite matrix in Oh symmetry explain the optical data, if we take into account the spin-orbit coupling and Jahn–Teller effect (JTE). Finally, an additional fluorescence has been found in the Tb3+-doped sample; it has been assigned to In+ ions in potassium sites.

Structural investigations of Mn 2+ ions in alkali barium borophosphate glasses by EPR and optical absorption techniques

Results are reported for electron paramagnetic resonance (EPR) and optical absorption structural investigations of Mn 2+ ions in alkali barium borophosphate glasses at room temperature. The Mn 2+ EPR hyperfine sextet centered at g = 2 was observed in all the glasses for 1 mol% Mn 2O 3. The absorption spectra of Mn 2+ ions in these glasses showed broad absorption bands characteristic of Mn 2+ ions in octahedral symmetry. From the EPR and optical results, it is concluded that the site symmetry around Mn 2+ ions is octahedral, and the nature of the bonding character is dominantly ionic.