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Optically Induced Conversion of Ge Centers in Quartz

An electron spin resonance (ESR) study of natural single crystalline quartz was performed to clarify the effect of ultraviolet rays (UV) exposure on electron traps at germanium impurities. ESR spectra of artificially γ-irradiated single crystalline samples from two different natural sites mainly showed a common Ge center, [Ge(C)e-/Li+], which is an electron trapped center at a Si-substituting Ge ion with a charge compensator of Li+. UV light exposure using a low-pressure mercury lamp converted [Ge(C)e-/Li+] into a different paramagnetic center. The observed ESR parameters of this center did not coincide with those of other known centers. This signal gradually decayed at room temperature and simultaneously produced a third center, Ge E2', which is a germanium dangling bond neighboring an oxygen vacancy with the form ≡Si–H •Ge≡. The experimental results indicated a two-step conversion of Ge centers, which was caused by UV exposure and aging. The total spin concentration was kept constant throughout the experiments.