Luminescence sensitivity changes in natural quartz induced by high temperature annealing: a high frequency EPR and OSL study

Quartz undergoes very significant luminescence sensitivity changes after hi gh temperature annealing (0-1200 degrees C), with particular enhancement oc curring between the phase transition temperatures 573 and 870 degrees C. In order to understand why this occurs, high frequency electron paramagnetic resonance (EPR), operating at 90 GHz, has been used to monitor the structur e and population of defects in natural sedimentary quartz, following anneal ing and gamma-irradiation. The results are compared with the optically stim ulated luminescence (OSL) data of the same samples. It is shown that: (i) t he structure and population of the dominant [AlO4](0) recombination centres are largely unaffected by the annealing process; (ii) the oxygen vacancy E ' centres are destroyed when annealed at temperatures between the phase tra nsitions and; (iii) the numbers of both [TiO4/H+](0) and [TiO4/Li+](0) dono rs increase between 400 and 700 degrees C. Photo-EPR spectra are presented, providing evidence that both the Ti associated donors and Al accepters are directly involved in the OSL process. The heat-induced changes in the popu lation of these EPR defects is mirrored in part by the change in the lumine scence sensitivity of several OSL components. Evidence is also presented su ggesting that E' may act as non-radiative centres competing in the OSL proc ess.