Dosimetric and spectroscopic study of LiMgPO₄ doped with Tm³⁺ and Er³

Olivine-type phosphate LiMgPO₄ doped with rare earth elements is considered a novel dosimetric material with excellent performance that is suitable for thermoluminescence (TL) and optically stimulated luminescence (OSL) measurements. Novel LiMgPO₄:Tm,Er samples were synthesized by a high-temperature solid-state reaction method. A detailed study of the TL and OSL of the samples was performed using β-ray irradiation and X-ray-excited optical luminescence (XEOL) spectroscopy. Density functional theory (DFT) calculations were performed to predict the preferential positions of thulium and erbium, and photoluminescence (PL) spectra and TL 3D spectra were analyzed. The DFT calculation results show that Mg is preferentially replaced by Tm/Er in the LiMgPO₄ system. The PL/TL3D/XEOL spectra of the samples are dominated by the characteristic luminescence of Tm³⁺, and the OSL decay curve of photoluminescence has fast and slow decay components with decay constants of 5 s and 42 s, respectively. The TL and XEOL results show that LiMgPO₄:Tm,Er has strong emission signals under different types of radiation rays. The PL/TL3D/XEOL spectral results show that Er³⁺ has no radiative excitation, but Tm³⁺ has strong luminescence, such that the sample still emits strong TL and PL signals. Two TL emission peaks occur at approximately 120 °C and 300 °C, where the high-temperature peak is significantly more intense than the low-temperature peak, promoting the stability of the TL and OSL signals of the samples. The TL curve consists of 6 general TL dynamic peaks. The nonlinear parameters of the TL dose response are R = 0.08 and D ₀ = 479 Gy, and the OSL dose response is linear in the range of 0.2-1000 Gy. The TL and OSL signals of the LiMgPO₄:Tm,Er phosphor have good repeatability. Therefore, the LiMgPO₄:Tm,Er phosphor can be used for radiation dose measurement.