Estimation of aluminum and growth-defect content in cultured quartz by using infrared absorption

The performance of quartz resonators and sensors is often limited by defects in the quartz. Of these defects, the substitutional aluminum with its charge-compensating ion and the OH-related containing growth defects are the most important. Quartz is grown in an alkali-rich environment and lithium (or sodium) are trapped interstitially next to the substitutional aluminum. Irradiation converts the Al-Li centers into a mixture of Al-OH and Al-hole centers. The Al-OH center is infrared active. Its bands can be used to determine the amount of Al-OH present after irradiation. Sweeping completely converts the Al-Li centers into Al-OH centers; again the infrared absorption can be used to determine the Al-OH content. We have calibrated the strength of the Al-OH absorption as measured at 80 K with the aluminum content. The aluminum concentration in swept quartz is found to go as 3.3 times the absorption coefficient of the 3367 cm^-1 Al-OH band. The OH-growth defects produce absorption bands at 3350, 3400, 3437, and 3581 cm^-1 , all four bands increase at the same rate with the crystal growth rate and decrease together when the sample is irradiated. Consequently, they arise from very closely related defects. They supply the hydrogen that is transferred to the Al-site during irradiation. We have some samples that have considerably fewer OH-growth defects than aluminum. In these samples all of the growth-defect hydrogen is transferred to the aluminum site. Thus, the resulting Al-OH absorption gives the initial OH-growth defect concentration. We have used these samples to obtain a calibration of the OH-growth defect concentration versus the 3581 absorption band. The OH-growth defect concentration is found to go as 8.3 times the absorption coefficient of the 3581 cm^-1 band