Optical and scintillation properties of Pr³⁺-doped Ca₃(BO₃)₂ single crystals

Optical and scintillation properties of Pr³⁺-activated Ca₃(BO₃)₂ (CBO) single crystals for neutron scintillator applications were examined. The crystals were grown by the micro-pulling down (μ-PD) method. In transmittance spectra, two absorption lines at 210 and 245nm were observed and they were identified as Pr³⁺ transition from the ground state ³H to 5d state. The both of photo- and radio-luminescence spectra of Pr³⁺-doped CBO crystals demonstrated intense peak at 260 and 310nm which was ascribed to the transition from the lowest 5d excited state to the 4f ground state levels of ³H. The main decay component was about 16-17ns under 245nm excitation wavelength. The relative scintillation light yield of 1.0% Pr³⁺-doped CBO was about 90% when compared with that of reference Li-glass scintillator (GS20) under ²⁴¹Am 5.5MeV α-ray excitation, while that measured under ²⁵²Cf neutron irradiation was about 20%. It was concluded that this difference originated from the difference of energy released from the neutron reactions.