Effect of the impurity charge state on the possibility of optically stimulated luminescence in magnesium tetraborates.

We studied ionizing radiation detectors in the form of magnesium tetraborate crystals doped with terbium and lithium or dysprosium (Dy) and sodium. The synthesized detectors were characterized by X-ray diffraction analysis. The spectrally resolved glow curve for the MgB4O7:Dy,Na sample was obtained, indicating the presence of Dy 3 + luminescence. The most intensive peak of radiation-induced absorption for MgB4O7:Dy,Na sample was detected within the 360–480 nm wavelength range. For optical excitation falling within this range, LEDs with different wavelengths were employed. Optical excitation caused partial erasing of the dose information in MgB4O7:Dy,Na. Analysis of theoretical luminescence models for magnesium borate-based materials confirmed that the stabilization of Dy in the tetraborate lattice occurs for Dy 2 + ions. Rare-earth element impurity level distribution in the MgB4O7 lattice was calculated according to the Dorenbos model. Analysis of this distribution led to a conclusion that for MgB4O7:Dy,Na, it is impossible to get optically stimulated signal. Nevertheless, it appears that MgB4O7:Tb,Li should have the possibility to register dose information optically. Thus, a new MgB4O7:Tb,Li material was synthesized. The presence of Tb 3 + ions in the structure was confirmed with the use of luminescence experiments. Results of thermoluminescence experiments for the MgB4O7:Tb,Li sample imply that there is a high-temperature peak at about 510 K. [ABSTRACT FROM AUTHOR]