Progress and challenges towards the development of a new optically stimulated luminescence (OSL) material based on MgB4O7:Ce,Li

Abstract

This work reports on the advances towards the development of a new optically stimulated luminescence (OSL) material based on MgB4O7:Ce,Li, which has high sensitivity to ionizing radiation, low effective atomic number (Zeff = 8.2), and fast luminescence when doped with cerium (Ce3+ emission). MgB4O7 samples doped with 0.3 mol% Ce and 10 mol% Li were synthesized by solution combustion synthesis (SCS) and annealed at various temperatures. The samples were characterized using photoluminescence, radioluminescence (RL), thermoluminescence (TL), and both blue- and green-stimulated luminescence (BSL and GSL). The OSL emission spectrum and sensitization were investigated as well. Further measurements of samples prepared with and without urea were carried out using differential scanning calorimetry (DSC), X-ray diffraction (XRD), TL and OSL to investigate the synthesis procedure. The results show that the use of high-purity Mg precursor in the MgB4O7:Ce,Li synthesis eliminates a competing recombination center emitting at ∼580 nm (possibly Mn2+), resulting in a ∼4.5 increase in the TL and the OSL in the UV region (290–390 nm). We have also confirmed that the OSL emission spectrum is characteristic of Ce3+ emission with two peaks at ∼335 nm and ∼355 nm due to the transition from the 5d to the 2F5/2 and 2F7/2 levels of the ground state configuration. Photoluminescence data confirms these emission bands and show the associated 4f → 5d excitation bands of Ce3+ at ∼270 nm, ∼293 nm and ∼320 nm. The luminescence lifetime associated with the Ce3+ emission was determined to be 31.5 ns. The OSL stimulation spectrum shows an increase in the OSL signal with an increase in the photon energy. The best annealing for the material prepared with high-purity Mg precursor was 700 °C for 2 with fast cooling, but no significant dependence on the annealing time or cooling regime was seen in the conditions investigated. Sensitization was observed in all TL and OSL measurements, but the TL sensitization was considerably reduced in the samples synthesized with high-purity Mg precursor. Additional studies by DSC, XRD, TL and OSL showed that, while the reaction was confirmed to be exothermic and higher TL and OSL signals were observed using urea, combustion is not essential to synthesize MgB4O7:Ce,Li with intense TL and OSL signals. In summary, MgB4O7:Ce,Li remains one of the most promising alternatives to the only two commercially available materials (Al2O3:C and BeO) in OSL dosimetry. Remaining challenges include to minimize the presence of shallow traps, which are likely responsible for the initial fading observed in the material, to better understand the nature of the TL and OSL sensitization in this material, and to find the optimum synthesis procedure to produce the material.