A peak structure in isothermal luminescence signals in quartz: Origin and implications

Isothermal heating is commonly used in luminescence dosimetry and trap parameter studies. It is often observed that the isothermal luminescence signal has a peak shape instead of a monotonous decay form. We provide here evidence that this peak shape in quartz may equally result from a 'thermal lag' problem in contrast to the earlier propositions of non first-order kinetics. Temperature modelling suggests that the peak-shaped signal contains elements of both the ramped - and isothermal - thermoluminescence (TL). The modelled changes in the peak movement as a function of isothermal temperature and the ramp-rate show an excellent agreement with those obtained experimentally. This understanding of thermal lag is extended to optically stimulated luminescence (OSL) measurements for which the effects of isothermal TL contamination and changing thermal assistance during thermal equilibration are discussed. Appropriate methods are suggested to identify thermal lag on the basis of the peak structure, and to circumvent this effect in isothermal methods.