Synthesis and characterization of Pr ³⁺-doped glass scintillators prepared by the sol-gel method

Transparent and crack-free Pr-doped silica glass scintillators were successfully synthesized using the sol-gel method. A peak found at 301 nm in the photoluminescence spectrum was ascribed to a radiative transition of the Pr ³⁺ emission center. The associated excitation peak was located at 276 nm. The energy of the excitation peak (4.50 eV) was significantly lower than the energy gap (5.83 eV) of the ¹S ₀ to ³H ₄ f-f transition. Therefore, the f-f transition was excluded as the origin, and the transition was attributed to 5d-4f. In the absorption spectrum, several bands of the f-f transition were observed. Fourier transform infrared spectroscopy was employed to understand the microstructural features and OH group concentration in the Pr ³⁺-doped silica glass. It was revealed that a Si-O network had been successfully formed, and that the OH group concentration decreased with increasing thermal treatment temperature reaching a saturation value for temperatures higher than 750 °C. The absence of praseodymium oxide nanocrystalline clusters was confirmed by transmission electron microscopy (TEM), even in the sample with the highest Pr ion concentration. Scintillation properties of the Pr ³⁺-doped silica glass were also characterized. The scintillation decay time constants were estimated to be approximately 1.3 and 14 ns, which supports the assignment of the luminescence to the 5d-4f transition. The scintillation light yield of the Pr ³⁺-doped silica glass was estimated to be approximately 130 photons/MeV.