Electron Paramagnetic Resonance Spectra Of Cr3 Research Articles

EPR, optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses

Antimony phosphate glasses (SbPO) doped with 3 and 6mol% of Cr3+ were studied by Electron Paramagnetic Resonance (EPR), UV–VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr3+-doped glasses showed two principal resonance signals with effective g values at g=5.11 and g=1.97. UV–VIS optical absorption spectra of SbPO:Cr3+ presented four characteristics bands at 457, 641, 675, and 705nm related to the transitions from 4A2(F) to 4T1(F), 4T2(F), 2T1(G), and 2E(G), respectively, of Cr3+ ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr3+ allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B=2.48 indicates that Cr3+ ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr3+ were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr3+-doped glasses excited with 350nm revealed weak emission bands from 400 to 600nm due to the 3P1→1S0 electronic transition from Sb3+ ions. Cr3+-doped glasses excited with 415nm presented Cr3+ characteristic luminescence spectra composed by two broad bands, one band centered at 645nm (2E→4A2) and another intense band from 700 to 850nm (4T2→4A2).

Phase transitions in K1− x Rb x Sc(MoO4)2 solid solutions

K1− x Rb x Sc(MoO4)2 single crystals doped with Cr3+ were studied by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy and optical microscopy. It has been found that the EPR spectra in solid solutions for x ≤ 0.2 are inhomogeneously broadened due to the random occupation of the next nearest-neighbour cation sites K+ and Rb+. The spin-Hamiltonian parameters describing the room-temperature EPR spectra of Cr3+ in K1− x Rb x Sc(MoO4)2 are calculated. The behaviour of the EPR spectra versus temperature reveals the existence of structural phase transitions in these crystals. The results show that a substitution of K+ by Rb+ suppresses the transition temperatures. The optical investigations carried out under the polarizing microscope have shown a ferroelastic nature of these transformations.

EPR and optical absorption of Cr3+ ions in ternary K2SO4-Na2SO4-ZnSO4 glasses

Electron paramagnetic resonance (EPR) spectrum of Cr3+ ions doped ternary K2SO4-Na2SO4-ZnSO4 glasses has been studied at different temperatures. The low field spectral resonance lines of the EPR spectra of Cr3+ ions in K2SO4-Na2SO4-ZnSO4 glasses are attributed to isolated Cr3+ ions whereas the high field spectral resonance line is attributed to exchange-coupled pairs of Cr3+ ions. The optical absorption spectrum of Cr3+ ions doped glass shows two broad bands characteristic of Cr3+ ions in octahedral symmetry. From the optical spectrum, the crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have been evaluated. From the EPR and optical spectral data, it is concluded that the site symmetry arround Cr3+ ions is octahedral and the nature of bonding is predominantly covalent in nature.

Off-axis extra lines in powder pattern electron paramagnetic resonance of Cr3+ in YAlO3

Powder sample electron paramagnetic resonance (EPR) spectrum of Cr3+ ions in YAlO3 crystals contains off-axis extra lines, which do not belong to the principal X, Y,and Z components of the fine structure. Orientation dependence of the EPR spectrum of Cr3+ doped YAlO3 single crystal confirms the existence of extra turning points corresponding to directions lying off the X, Y, and Z axes, consistent with theoretical predictions. This results in five EPR lines due to the transition between the central Kramers doublet in the powder system. The observed powder pattern EPR has been used in identification of Cr3+ as an impurity ion in undoped YAlO3 crystals.

Electron paramagnetic resonance and optical spectra of Cr3+-doped YAlO3

This paper reports electron paramagnetic resonance (EPR) measurements of Cr3+ ions in YAlO3 (YAP) at 1.6 K and room temperature along with their optical absorption and luminescence spectra The polarization of the excitation spectrum of the Cr3+ luminescence has also been measured. The EPR spectrum is ascribed to substitutional Cr3+ ions at Al3+ sites. The spin-Hamiltonian parameters determined from the EPR spectrum of Cr3+ ions in nearly orthorhombic sites in YAP are gx = 1.981, gy = 1.981, gz = 1.981, b20 = +445 * 10-4 cm-1 and b22 = -278 * 10-4 cm-1. The anisotropy of the Cl3+ EPR spectrum is discussed in terms of the electrostatic potential of the surrounding O2- and Y3+ ions in YAP crystals and is compared with that of Ti3+ ions in the same host crystal.