## 4 Conclusions  
1.0% Tb-doped LPS, YPS, GPS, and LaPS single crystals are successfully grown by the floating-zone technique. The single phase of each rare-earth pyrosilicate is validated by powdered XRD analysis. PL properties of the samples are investigated including multiple emissions characterized by the strongest emission at 540 nm of Tb\({}^{3+}\) 4f-4f transitions on PL emission contour graphs, and the PL decay times of the present samples are 2.62-5.65 ms. In scintillation properties, X-ray induced scintillation spectra of the samples have presented similar emission peaks with PL. The scintillation decay times of the samples resulted in 1.35-3.21 ms. The Tb-doped YPS and GPS present a high afterglow level (Af\({}_{20}\)) at around 3500-3800 ppm. Under 662 keV \(\gamma\)-ray irradiation by \({}^{137}\)Cs, the Tb-doped  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Name** & **Scintillation Light Yield (ph/MeV)** & **Energy Resolution (\%)** \\ \hline Tb-doped LPS & 20,700 & 15.2 \\ Tb-doped YPS & 29,600 & 10.6 \\ Tb-doped GPS & 95,600 & 30.3 \\ Tb-doped LaPS & 47,700 & 16.8 \\ BGO & 8200 [60] & 26.9 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Absolute scintillation light yields and energy resolution of the Tb-doped pyrosilicate samples under 662 keV \(\gamma\)-ray irradiation.  
Figure 9: Pulse-height spectra of Tb-doped LPS, YPS, GPS, and LaPS samples, under the \({}^{137}\)Cs (662 keV) \(\gamma\)-ray. With the spectrum of the BGO reference sample.  
pyrosilicate samples present high scintillation light yield, and especially Tb-doped GPS shows 95,600 ph/MeV with the energy resolution of 30.3%. The Tb-doped LaPS exhibits the second highest scintillation light yield in this study with 47,700 ph/MeV with an energy resolution of 16.8%. To the presented results, Tb-doped GPS and LaPS are suitable candidates for the novel scintillator. However, Tb-doped pyrosilicate materials have scintillation decay time in the ms-range. Therefore, the possible applications are the ones that favor brightness over the response time such as the scintillator screen for X-ray radiography. In the future work of these materials, the Tb-doped concentration dependence and the other method of crystal growth are recommended for the Tb-doped GPS and LaPS for improving and better understanding properties of these compounds.  
Conceptualization, P.K.; methodology, P.K., K.W. and T.Y.; validation, T.K., D.N. and N.K.; formal analysis, P.K. and T.Y.; investigation, P.K., K.W. and T.Y.; resources, K.W. and T.Y.; data curation, P.K. and N.K.; writing--original draft preparation, P.K.; writing--review and editing, P.K.; visualization, P.K.; supervision, T.Y.; funding acquisition, T.K., D.N., N.K. and T.Y. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Cooperative Research Project of the Research Center for Biomedical Engineering, Nippon Sheet Glass Foundation, and Iketani Science and Technology. In addition, the Japan Society for the Promotion of Science (JSPS) is also acknowledged for Grant-in-Aid for Scientific Research A (22H00309), B (21H03733, 21H03736, and 22H02939), Grant-in-Aid for Exploratory Research (22K18997), and Early-Career Scientists (20K20104).  
Not applicable.  
Data of the results presented in this article are not publicly available.  
Radiation Physics and Measurement Laboratory, Department of Applied Quantum Physics and Nuclear Engineering, Faculty of Engineering, Kyushu University is acknowledged for providing the measurements system and data curations.  
The authors declare no conflict of interest.