Defect centre responsible for production of 110 ∘ C TL peak in quartz

Abstract

110 ∘C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO 4 tetrahedron and under irradiation gives rise to [GeO 4/e −] − electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO 4/h] ∘ or [H 3O 4/h] ∘ centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 ∘C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g 1=2.0004, g 2=1.9986 and g 3=1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 ∘C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O − centre.