Anomalous heating rate effect in thermoluminescence intensity using a simplified semi-localized transition (SLT) model

Abstract

During thermoluminescence (TL) measurements carried out with different heating rates, one expects the total number of emitted photons to be constant. However, for many luminescence materials one observes a decreased intensity of luminescence at elevated temperatures, due to the presence of the well-known phenomenon of thermal quenching. Recent experimental work on the dosimetric material YPO4 double doped with lanthanides demonstrated the exact opposite behavior, in which the total luminescence intensity increases with the heating rate during the TL experiments. This anomalous TL behavior was recently explained by using the Mandowski model of semi-localized transitions (SLTs). In this paper it is shown that this anomalous heating rate or “anti-quenching” phenomenon can also be described by using a simplified SLT model of TL with approximated kinetic equations. The simulated glow curves show that as the probability of the non-radiative processes increases, the anomalous heating rate effect becomes dominant. The dependence of the anomalous heating rate effect on the values of the kinetic parameters in the model is examined by allowing random variations of the parameters in the model, within wide ranges of physically reasonable values covering several orders of magnitude. It is shown by simulation that the variable heating rate method can systematically underestimate the value of the activation energy E, while by contrast the initial rise method of analysis almost always yields the correct E value. These simulated results are discussed in relation to recent experimental work on the double doped dosimetric material YPO4.