Knowledge Bank

The $3\mu$ absorption spectra of $\alpha$-quartz crystals at $\sim 77\circ K$ exhibit sharp bands which are known to be due to OH in various types of site. The extinction coefficients of these bands vary from sample to sample and are affected by such treatments as electrolysis in vacuum and in air, annealing, electrodiffusion, and x- and $\gamma$-irradiation. Bonded OH causes a broad background absorption on which the sharp bands are superimposed. When alkali ions are present in natural quartz, certain sets of sharp absorption bands are seen. It is known that each set is characteristic of an OH group associated with an alkali ion. If $Li+$ is electrodiffused into synthetic quartz, we find that the resonator properties indicate its presence. The fact that, in this case, the absorption spectrum does not show the alkali'' bands indicates that here there are no $Li^{+}$ ions associated with OH. On the other hand, if $Li^{+}$ is in-incorporated during the growth of synthetic quartz, it apparently enters other sites because alkali'' bands appear in the spectrum. The spectra of several samples from different regions of a crystal which had been fast grown in a $Li+$ doped solution indicate more bonded OH near the seed and more alkali near the surface of the crystal. This agrees reasonably well with color center studies.