## 1 Introduction  
Sensitization is known as the increased luminescence response of a material as a result of a certain test dose after thermal activation [1, 2, 3, 4, 5]. Two methods are used to produce sensitization: One is to irradiate the specimen with a high dose and after that treat it thermally to an activation temperature [6, 7], while the other is to anneal the sample at high temperature [8]. The first method of sensitization is called the pre-dose effect [9]. This method of sensitization is extensively used in authenticity testing of natural materials and other fields [10]. Others use the optimum particle size [11]. Over time, many models have been proposed to explain the phenomena of sensitization [5, 12]. Thermal sensitization is obtained by annealing the investigated sample at higher temperatures. Thermal treatments of the investigated sample at higher temperature leads to the removal of competitors and, consequently, alterations of the recombination centers at these temperatures [13, 14]. Thus, high-temperature annealing creates additional recombination centers (L) and, as a result, increases the number of holes that are captured during subsequent irradiation cycles, which improves sensitivity [12, 15]. Attempts were made to elucidate the tendency of mixing up these forms of sensitization [16]. The thermal sensitization method is the main form of sensitization in unheated samples, while the pre-dose method is the prominent effect of the sensitization of annealed samples [15]. Doping is also another important factor affecting TL sensitization [17]. Additionally, the thermal history of a material, which includes the heating conditions, has also a significant bearing on its luminescence characteristics [12, 18, 19]. The sensitization method was also investigated for synthetic materials [20].  
It has been previously reported that the TL dose responses of some natural materials are sublinear, for example, dolomite, calcite, and tuff, while a few are superlinear, such as amethyst quartz [10] and feldspar. In the present study, we report for the first time sensitization studies of naturally grown phyllite material, which is not similar to any previous reports of natural materials [4, 11, 18, 19, 20, 21, 22].  
Other natural materials were studied, including quartz [7], mica [21, 22, 23], blue calcite [24], and calcitic limestone [13]. For example, [PERSON] et al. [23] studied the sensitization characteristics of the 180 \({}^{\circ}\)C thermoluminescence peak of muscovite mica. They investigated the relationship between the sensitization factor and the pre-dose and duration of heat treatment. [PERSON] [22] was reported the effect of pre-dose on the natural white mica. The author found that a pre-dose of 1 kGy of gamma-radiation, followed by thermal activation to 550 \({}^{\circ}\)C of fired mica, causes a notable increase in TL sensitivity. [PERSON] et al. [14] investigated TL properties for natural quartzes using IPDA and TLCI methods. They found a change in color from original blue to red in a Z-cut slice of Madagascar quartz due to the annealing (at about 1000 \({}^{\circ}\)C). [PERSON] et al. [24] studied the TL for quartz and found that the TL response of the quartz is improved by 2-3 orders when the specimen received a pre-gamma exposure of about 10/sup 7/R.  
The main aim of the present investigation is to study the sensitization resulting from both thermal activation and a pre-dose of 250 \({}^{\circ}\)C TL peak. A focus on the competitor deep electron traps far from thermal quenching effects was identified by experimental glow curve deconvolutions. The pre-doses (0.1-1.75 kGy) used in this study, and the dose-response ranges (0.1-1000 Gy) are much wider than those in previous reports.