Hydroxyl defects in germanium-doped quartz: Defect dynamics and radiation effects

Abstract

Irradiation effects on near-infrared absorption bands have been studied in a variety of Ge-doped cultured quartz crystals. The irradiation was done at 77, 300, and finally again at 77 K in a sequence. Extended radiation doses upon final irradiation at 77 K exhibited the presence of a defect center absorbing at 3400 cm{sup {minus}1}, which increased linearly with accumulated radiation dose. Another small band at 3602 cm{sup {minus}1} is observed in a sample grown quickly. A Ge-doped crystal grown under high pressure and a Premium {ital Q} crystal did not exhibit either of these bands. While the 300-K irradiation produced the Al-OH{sup {minus}} bands in all samples, their strength was augmented from the as-received condition for the crystal grown under high pressure. Isochronal annealing showed that the low-temperature irradiation-induced band at 3400 cm{sup {minus}1} stayed constant in the 120--180 K temperature region and decayed sharply to nearly 15% of its maximum strength in the 180--200 K temperature range. The depletion of this band matched with the onset of recovery of the conventional growth defect bands in conjunction with the increase of 3602 cm{sup {minus}1} band in this temperature region. This shows that these two defects centers absorbing at 3602 andmore » 3400 cm{sup {minus}1} arise from an interrelated configuration of hydroxyl point defects. The 3400 cm{sup {minus}1} radiation-induced band represents a Ge-H-Li complex of the form [Ge{sup 4+}{ital e}{sup {minus}}{ital M}{sup +}{ital e}{sup {minus}}H{sup +}]{sup 0}. A comparison of Ge-doped crystals with Sawyer Premium {ital Q} quartz has been presented on the radiation response characteristics for the irradiation cycle used and the results are discussed in terms of fundamental considerations governing defect dynamics in crystalline quartz.« less