X-ray induced Sm-ion valence conversion in Sm-ion implanted fluoroaluminate glasses towards high-dose radiation measurement

Ion implantation of Sm-ions has been tested in fabricating 2D detectors for microbeam radiation therapy (MRT). Sm-ions have been successfully implanted into fluoroaluminate (FA) glasses. The implantation concentration was chosen to be 5 × 10¹⁵ ions/cm² and the ions were implanted at an energy of 2 MeV. After implantation, samarium ions resided within a thin plane very near the surface in the glass, which is expected to be beneficial for 2D imaging. Following implantation, photoluminescence (PL) spectra indicate that the embedded Sm-ions are in the form of Sm²⁺ and Sm³⁺. Subsequent annealing around the glass transition temperature (475 °C) converts all Sm²⁺ ions into Sm³⁺. Under X-ray irradiation, a partial conversion of Sm³⁺ into Sm²⁺ has been observed which may be used as measure of the X-ray dose delivered into the sample. QFRS (quadrature-frequency-resolved-spectroscopy) measurements on PL prominent emissions from Sm³⁺ and Sm²⁺ ions show that the PL decays associated with various transitions are in the 0.1 to 100 ms range (slow transitions). X-ray irradiation has led also to the appearance of broad and intense photoluminescence bands associated with X-ray induced structural defects in the host glass as confirmed in the unimplanted FA glasses. The generation of hole trapping centers in the host glass leads to the capture of photogenerated holes and thus allows the electrons to convert Sm³⁺ to Sm²⁺. Defect related PL decay signals were measured to be in the nanosecond region. These unwanted defect related fast decaying signals have been separated from slow Sm²⁺ and Sm³⁺ photoluminescence signals by using an “out-of-phase” PL measurements through a phase-sensitive photodetection technique with a modulated excitation laser diode and a lock-in amplifier. Overall, the Sm-ion implanted fluoroaluminate glass shows the successful conversion from the trivalent form of samarium (Sm³⁺) to the divalent form (Sm³⁺) under X-ray irradiation over a large dynamic range of X-ray intensities (800 Gy in air).