Electron Spin Resonance and Optical Absorption Studies of Cr3+ in a Phosphate Glass

Abstract

Optical absorption and electron spin resonance (ESR) spectra of a chromium‐doped phosphate glass have been studied as a function of Cr₂O₃ concentration. While the optical spectrum appears to be independent of chromium‐ion density, the ESR spectrum exhibits a pronounced concentration dependence. The spectra have been attributed to a combination of isolated, octahedrally coordinated Cr³⁺ and antiferromagnetically coupled pairs of Cr³⁺ ions which are individually sixfold coordinated. The measured value of the crystal‐field parameter Δ is 14 500 cm⁻¹. The ESR data are analyzed within the framework of the spin‐Hamiltonian formalism. In the case of the isolated Cr³⁺ it is estimated that the axial field parameter | D | lies in the range 0.15 to 0.5 cm⁻¹. The assumption of a relatively strong isotropic exchange interaction is adequate to describe the gross features of the Cr³⁺ pair spectrum. Speculative models for the glass structure in the neighborhood of an isolated Cr³⁺ ion and a Cr³⁺ pair are presented.