Electron Spin Resonance and Optical Absorption in GeO2

Abstract

Paramagnetic states of GeO₂ in the glass and in the powdered crystalline hexagonal and tetragonal phases have been investigated by the means of electron spin resonance after irradiation with γ rays and electrons. Three of the resonances observed in the glass were identified as intrinsic paramagnetic states on the basis of concentration, g values, and the shapes of the resonances. The g values of these lines were 1.9957, 2.0060, and 2.0080. The g=1.9957 line had a shape which was invariant with temperature (300°, 78°, and 2°K) and with magnetic field. The shape was a characteristic powder pattern for a center with S=½ and an approximately axially symmetric g tensor, where g_‖=2.0016 and g_⊥=1.9957. This line was characteristic of all glass and hexagonal crystal‐phase specimens for all irradiations at temperatures∼300°K. The spin concentration after an irradiation of ∼10¹⁷ (1.5 meV) electrons cm⁻² was ∼3×10¹⁸ cm⁻³ with no indication of saturation. Tentative correlation of this paramagnetic center with optical absorption in the region of 4.5 eV was established by a series of irradiations and subsequent heat treatments. The data on the g=1.9957 line was sufficient for the proposal of a model in which an electron is trapped at an oxygen vacancy. The g=2.0080 line was observed in all electron‐irradiated glass specimens and the g=2.0060 line was found in all γ‐ray irradiated glass specimens along with the g=2.0080 line. Other lines were observed at lower g values in β and γ irradiated glass and were tentatively assumed to be due to impurities. Irradiation of the glass with ⁶⁰Co γ rays at 78°K and measurements without intervening warmup showed only one resonance with g=1.9957 but with a shape quite different from the g=1.9957 line found after irradiation with the same dose of ⁶⁰Co γ rays at approximately 40°C. This line was assumed to be another intrinsic center. Resonances observed in the tetragonal‐phase powder bore no relation to the resonances in the glass and hexagonal‐phase powder.