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

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 ${\mathrm{cm}}^{\mathrm{-}1}$, which increased linearly with accumulated radiation dose. Another small band at 3602 ${\mathrm{cm}}^{\mathrm{-}1}$ is observed in a sample grown quickly. A Ge-doped crystal grown under high pressure and a Premium Q crystal did not exhibit either of these bands. While the 300-K irradiation produced the Al-${\mathrm{OH}}^{\mathrm{-}}$ 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 ${\mathrm{cm}}^{\mathrm{-}1}$ 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 ${\mathrm{cm}}^{\mathrm{-}1}$ band in this temperature region. This shows that these two defects centers absorbing at 3602 and 3400 ${\mathrm{cm}}^{\mathrm{-}1}$ arise from an interrelated configuration of hydroxyl point defects. The 3400 ${\mathrm{cm}}^{\mathrm{-}1}$ radiation-induced band represents a Ge-H-Li complex of the form [${\mathrm{Ge}}^{4+}$${\mathit{e}}^{\mathrm{-}}$${\mathit{M}}^{+}$${\mathit{e}}^{\mathrm{-}}$${\mathrm{H}}^{+}$${]}^0$. A comparison of Ge-doped crystals with Sawyer Premium 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.