ESR, optical absorption, and luminescence studies of the peroxy-radical defect in topaz

Abstract

Fast-neutron irradiation of natural topaz crystals produces a single paramagnetic radiation damage center in high concentration. ESR of this center shows a holelike spectrum with S=1/2 and a strongly anisotropic g tensor: ${\mathit{g}}_{\mathit{x}\mathit{x}}$=2.0027, ${\mathit{g}}_{\mathit{y}\mathit{y}}$=2.0055, and ${\mathit{g}}_{\mathit{z}\mathit{z}}$=2.0407. We identify this defect as an intrinsic ${\mathrm{O}}_{2}^{\mathrm{\ensuremath{-}}}$ center in the form of a peroxy radical. The orientation of the g tensor helps confirm this assignment, as does the extraordinary thermal stability; annealing temperatures near 800 \ifmmode^\circ\else\textdegree\fi{}C are required for complete removal. Two uv absorption bands are associated with the peroxy radical, each with oscillator strength near 0.09. Pumping in the higher energy band leads to a polarization-sensitive 2.5-eV luminescence; the other uv band apparently relaxes nonradiatively.