Radiation effects in natural quartz crystals

Optically clear, as visually observed, natural quartz crystals of Brazilian and Arkansas origins, which exhibit Al–OH–-centers in their as-received conditions,have been measured for their low temperature ESR spectra to see the presence of Al-hole centers. The ESR spectra revealed the presence of Al-hole centers in their as-received conditions. These centers showed an increase in their strength upon irradiation with a 60 C0 source. Such observations were exhibited by Al–OH-centers as noticed earlier. The crystals were thus noticed to exhibit the presence of Al–OH– -centers and also Al-hole centers in their as-received conditions. The observations match with the results on cultured quartz where irradiation breaks away the Al-alkali centers into a mixture of Al–OH–- and Al-hole centers. It is thus concluded that the natural crystals,which exhibit the presence of these centers in their as-received condition, have been irradiated in nature with a low dose

Characterization of the E1′ center in quartz: Role of aluminum hole centers and oxygen vacancies

The growth of E1′ centers in a variety of natural and synthetic quartz crystals has been investigated by employing the electron spin resonance technique. It has been reported that the growth of E1′ centers, formed by irradiation and subsequent annealing at 300 °C for 15 min, scale with the concentration of the aluminum hole center, [AlO4]0, till a limit. Later, the E1′ centers show saturation even when the [AlO4]0-center continues to grow. For quartz with low efficiency of the formation of [AlO4]0-center or irradiated with low accumulated doses, the intensity of E1′ center was small where not all oxygen vacancies are converted to the E1′ center. Thus, besides the availability of a number of oxygen vacancy sites, the number of holes released from the [AlO4]0-center plays an important role in the formation of E1′ centers in quartz