## 3 Results and Discussions
### Scintillation Properties  
Figure 6 presents X-ray induced scintillation spectra of Tb-doped LPS, YPS, GPS, and LaPS samples. All of the samples have the same spectral shape. Furthermore, the scintillation wavelengths observed here are similar to the emission wavelength with the results of PL emission. In addition, the scintillation from Tb\({}^{3+}\) 4f-4f transitions including 380 (\({}^{5}\)D\({}_{3}\rightarrow{}^{7}\)F\({}_{6}\)), 420 (\({}^{5}\)D\({}_{3}\rightarrow{}^{7}\)F\({}_{5}\)), 440 (\({}^{5}\)D\({}_{4}\rightarrow{}^{7}\)F\({}_{5}\)), 480 (\({}^{5}\)D\({}_{4}\rightarrow{}^{7}\)F\({}_{6}\)), 540 (\({}^{5}\)D\({}_{4}\rightarrow{}^{7}\)F\({}_{5}\), strongest), 590 (\({}^{5}\)D\({}_{4}\rightarrow{}^{7}\)F\({}_{4}\)), and 620 nm (\({}^{5}\)D\({}_{4}\rightarrow{}^{7}\)F\({}_{3}\)) are founded in all sample. In terms of spectral shapes, the scintillation spectra of Tb-doped pyrosilicate samples are comparable to the other Tb-doped scintillator study. Because the intensity value (vertical axis) in this measurement is qualitative, the comparison of scintillation light yield is discussed in the pulse-height spectra results. Figure 5: PL decay time profiles of Tb-doped LPS, YPS, GPS, and LaPS samples. Observation and excitation wavelength are 550 and 340–390 nm, respectively. Figure 6: X-ray induced scintillation spectra of Tb-doped LPS, YPS, GPS, and LaPS samples. Figure 7 illustrates the X-ray induced scintillation decay time profile of each Tb-doped LPS, YPS, GPS, and LaPS sample. The decay time profile is approximated with a sum of two exponential decay functions. The 1 st decay constant of all samples is influenced by the IRF which appears at the initial part of the profile as a very fast component. On the other hand, the 2 nd decay constant of the samples is ascribed to the scintillation from the Tb\({}^{3+}\) 4f-4f transitions. When comparing with the previous results of PL decay times, every sample has shown a faster scintillation decay constant [69]. This phenomenon may be caused by the wavelength sensitivity of this measurement from 160 to 650 nm. In PL, only the emission at 540 nm is focused by using optical filters while the current measurements accumulate all the emissions from 160 to 650 nm. The afterglow timing profiles of Tb-doped LPS, YPS, GPS, and LaPS samples and \(Af_{20}\) values are exhibited in Figure 8. In comparison with the commercial scintillator on the market, Tb-doped pyrosilicate samples have relatively higher afterglow levels than the CdWO\({}_{4}\) (CWO) and Tl-doped CsI which have \(Af_{20}\) around 100 and 268 ppm, respectively [70; 71]. One of the main reasons for the Tb-doped pyrosilicate sample's high afterglow level is the slow scintillation decay time in the ms region. Figure 9 presents the pulse-height spectra of Tb-doped pyrosilicate samples, under the \({}^{137}\)Cs (662 keV) \(\gamma\)-ray irradiation, plotted with the spectrum of the BGO reference sample. For the scintillation light yield, the calculation is done by taking into consideration the different quantum efficiencies of the PMT on both scintillation wavelengths of Tb-doped pyrosilicate (540 nm, 9%) and BGO reference (480 nm, 25%). It means, although photoabsorption peak channels of Tb-doped YPS and reference BGO are close, after the  
Figure 8: Afterglow profiles of Tb-doped LPS, YPS, GPS, and LaPS samples, with the \(Af_{20}\). Figure 7: X-ray induced scintillation decay time of Tb-doped LPS, YPS, GPS, and LaPS samples. correction of quantum efficiency of PMT, Tb-doped YPS sample will have the scintillation light yield 2.77 time higher than the BGO reference. The calculated scintillation light yield with an energy resolution of each sample and BGO reference are summarized in Table 1. Among all of the Tb-doped pyrosilicate samples in this study, the Tb-doped GPS has presented the highest scintillation light yield of 95,600 ph/MeV.