3.3.1. Sample Optimization

The samples were exposed to 3 Gy of X-ray radiation. Figure 8 displays the glow curve of the dosimetric peak for ZnO and Ag-doped ZnO thin films. The acquired glow curve exhibited a single peak sited at 240–270 ◦C with 5 ◦C/s of the heating rate. The results showed that the highest intensity of the thermoluminescence corresponded to a 0.5 mol% Ag-doped ZnO sample at 270 ◦C. This temperature peak is a desirable site for the dosimetry application because, if located at a low temperature, it will cause an increase in the fading and a loss of the signal, similar to if the dosimetric peak is situated at a high temperature, which leads to an interface with black body radiation as reported [25,68]. As the concentration of Ag decreased, the TL intensity appeared to increase, with a noticeable shift toward higher temperature.

The emission of TL intensity for Ag-doped ZnO increased when the dopant ratio reached 0.5%. Beyond this concentration, the Ag atoms became agglomerated into metallic Ag clusters, reducing the surface defects and, thus, quenching the TL intensity [69,70].

Another fact is that Ag-doped ZnO does not create a new TL peak but increases the trap center, increasing TL intensity. For more explanation of the TL mechanism of Ag-doped ZnO, when the samples were irradiated (the photon energy of X-ray was more significant than the bandgap of ZnO), the electrons in the valence band of this nanocomposite excited to the conduction band (*e*<sup>−</sup>) simultaneously produce an equal number of holes (*h+*) in the valence band. These electrons and holes will relax at the tarps created by the oxygen vacancies and Ag+ ions, preventing the immediate recombination of (*e*<sup>−</sup> − *h*+) pairs. Consequently, the electrons and holes will stay trapped for a long time, depending on the

lifetime of the levels trapped and the ambient temperature; later, when stimulated, the samples via the temperature, electrons, and holes will recombine at the recombination center, and emission photons will occur. The optimized sample of 0.5%Ag-doped ZnO was chosen for further investigations.

$$\text{ZnO/Ag} + + \text{radiation} \rightarrow \text{ZnO/Ag} \left(e^-\_{cb} + h^+\_{vb}\right)$$

$$(\mathfrak{e}\_{cb}^- + h\_{vb}^+) \to \overset{recombined \text{ at } LM \text{ center}}{\longrightarrow} \text{ emission light}$$

**Figure 8.** The glow curves of Ag-doped ZnO thin films with different concentrations of Ag percentage.
