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 Cr 2O3 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.