Defect Structure of Crystalline Quartz. I. Radiation-Induced Optical Absorption

Abstract

Low-temperature bombardment (77\ifmmode^\circ\else\textdegree\fi{}K) of synthetic crystalline quartz with fast electrons induces optical absorption ($C$ band) near 220 m\ensuremath{\mu}. For 40\ifmmode^\circ\else\textdegree\fi{}C neutron irradiations the absorption maximum is near 210 m\ensuremath{\mu}. The absorption has an orientation dependence when produced by electron irradiation. This dependence is exhibited by a shift in the position of maximum absorption from 220 m\ensuremath{\mu} for samples cut perpendicular to the $c$ axis ($Z$ cut) to 217 m\ensuremath{\mu} for samples cut parallel to the $c$ axis ($Y$ cut). The absorption in the $Z$-cut samples is about twice that of the $Y$-cut samples for equal integrated flux. In neutron-irradiated material no such dependence is noted. The defect giving rise to the $C$-band absorption anneals near 225\ifmmode^\circ\else\textdegree\fi{}C. The electron or hole occupying the defect, however, is relased below room temperature, removing the optical absorption. After heating to temperatures below 225\ifmmode^\circ\else\textdegree\fi{}C, the original absorption obtained after electron irradiation at 77\ifmmode^\circ\else\textdegree\fi{}K can be regained by a brief re-irradiation at 77\ifmmode^\circ\else\textdegree\fi{}K (0.01 of the original integrated flux). A similar electron exposure at low temperature augments the absorption induced by fast neutrons at 40\ifmmode^\circ\else\textdegree\fi{}C and introduces a strong absorption at 230 m\ensuremath{\mu} which was not previously discernible. The magnitude of the $C$-band absorption in electron-irradiated material is strongly dependent on the crystal growth rate, increasing by a factor of about 17 for a growth rate increase of 4.5. The increase for the band produced by neutron bombardment [5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ nvt (fast)] is only about 25%. The comparison of electron irradiation and x-ray bombardments, and noncorrelation of absorption with impurity content, indicate that the defect responsible for the $C$-band absorption is produced by direct Coulomb encounters with lattice constituents.