EPR and optical absorption studies of Fe3 ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe3 ions doped sodium borophosphate glasses (NaH2PO4B2O 3Fe2O3). 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 Fe3 ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe3 ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123295 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 (Ï) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θp) have been evaluated from the 1/Ï versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe3 ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed. © 2010 Elsevier Ltd

EPR, optical absorption and photoluminescence properties of Cr3+ ions in lithium borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence studies of Cr3+ 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 Cr3+ ions and exchange coupled Cr3+ 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 (Ï) was calculated from the EPR data. It is observed that as temperature decreases, Ï increases in accordance with Curie-Weiss law. The exchange coupling constant J between Cr3+ 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 Cr3+ 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 4T2g (F) â4A2g (F) ground state of Cr3+ ions. The optical band gap is evaluated from the ultraviolet absorption edges. © 2010 Elsevier B.V. All rights reserved

EPR and photoluminescence studies on lithium-potassium borophosphate glasses doped with Mn2+ ions

The mixed alkali borophosphate xLi2O-(30 - x)K2O-35B2O3-34.5P2O5 (5 â x ⤠25) glasses doped with 0.5 mol of manganese ions have been studied using EPR and photoluminescence techniques. The EPR spectra of all the investigated samples exhibit resonance signals which are characteristic of Mn2+ ions. The resonance signal with effective g value at g = 2.02 exhibits a six line hyperfine structure. The zero-field splitting parameter (D) at room temperature has been evaluated from the intensities of allowed hyperfine lines. The EPR spectra at different temperatures (123-295 K) have also been studied. It is found that the spin concentration (N) exhibits non-linear behaviour with composition showing the mixed alkali effect (MAE). From the EPR data, the paramagnetic susceptibility (Ï) has been calculated at various temperatures. The Curie constant (C) and paramagnetic Curie temperature (θp) have been evaluated from the 1/Ï versus T graph. The photoluminescence (PL) spectrum exhibits a green emission band at 582 nm and this band has been assigned to a transition from the upper 4T1g â6A1g ground state of Mn2+ ions. © 2009 Elsevier B.V. All rights reserved