Thermoluminescence response of previously heated NaCl : Eu crystals to UV radiation

Abstract

In this work we report the modification in the thermoluminescent (TL) response to ultraviolet (UV) radiation of Czochralski-grown NaCl : Eu crystals when they are pre-heated. The crystals were pre-heated at 273, 473, 573, 673, 773 and 873 K for 2 h in an inert atmosphere, observing the highest response in crystals pre-heated at 573 K and the lowest in crystals pre-heated at 473 K. To correlate the TL response with the thermal treatment and, in a certain way, with the microstructure developed in the crystals, they were observed with a low vacuum scanning electron microscope. At 373 K the crystals showed spherical precipitates of 100 nm size homogeneously distributed, whereas at 473 and 573 K, the crystals showed, besides spherical precipitates, wire-like precipitates from 1.0 to 7.0 µm in length. The precipitates changed to a square 4 µm in size at 673 K which diminished to 1.0 µm in size in crystals heated at 773 and 873 K. Clearly the shape of the precipitates has an influence on the TL response of the NaCl : Eu crystals.

Adaptation of the OTOR-model to explain exactly the thermoluminescence processes during thermal excitation

“…The general-order expression ( 4) is fitted to the glow curves derived from the M-OTOR-model. This also means that the results of the M-OTOR model are in agreement with the experimental results where the shapes of most experimental TL glow peaks which are obtained from different TL materials do not change with increasing dose [12,[25][26][27][28][29][30][31][32][33][34][35][36][37]. Some of these recent experimental results which agree with the M-OTOR-model are found in the literature [12,27,28,31,[33][34][35].…”

“…During studies on the TL phenomenon, it has been observed firstly that the shape of most experimental glow peaks obtained from different TL materials do not change with increasing the dose, see for example [12,[25][26][27][28][29][30][31][32][33][34][35][36][37]. This means that the values of the order of kinetics b of these glow peaks do not change with increasing absorbed dose [27,38,39].…”