Unlocking the effect of Li and Ce ions on the thermoluminescence and optically stimulated luminescence signals of the MgB4O7 compound.

Magnesium tetraborate (MgB4O7) is an example of a material that has attracted the attention of researchers in the field of ionising radiation dosimetry. Several challenges are present in order to achieve considerable advances in luminescence dosimetry. The incorporation of efficient dopants in the host matrix has been an experimentally useful but limited strategy. The lack of specific information about the introduced defects as well as their connection with the trapping and recombination processes associated with light emission may be quoted as challenging examples. Here, we demonstrate the influence of lithium incorporation on Optically Stimulated Luminescence (OSL)/Thermoluminescence (TL) signal modification/suppression of MgB4O7 by combining experimental and computational procedures. Li substitution into the Mg site leads to a signal suppression due to the probable quenching of the Fs and Fs+ centres in MgO and the formation of O''i, drastically reducing the possibility of MgO anti-Schottky defect formation in MgB4O7. When using Li-co-doped MgB4O7:Ce3+, the Li ions act as a charge balancer, facilitating the entry of Ce ions into the interstitial pores and making possible a positive synergistic effect on the luminescence and dosimetric properties. These findings provide new insights into designing more efficient dosimeters by tuning dopants.

Highly-sensitive Eu(3+) ratiometric thermometers based on excited state absorption with predictable calibration.

Temperature measurements ranging from a few degrees to a few hundreds of Kelvin are of great interest in the fields of nanomedicine and nanotechnology. Here, we report a new ratiometric luminescent thermometer using thermally excited state absorption of the Eu(3+) ion. The thermometer is based on the simple Eu(3+) energy level structure and can operate between 180 and 323 K with a relative sensitivity ranging from 0.7 to 1.7% K(-1). The thermometric parameter is defined as the ratio between the emission intensities of the (5)D0 → (7)F4 transition when the (5)D0 emitting level is excited through the (7)F2 (physiological range) or (7)F1 (down to 180 K) level. Nano and microcrystals of Y2O3:Eu(3+) were chosen as a proof of concept of the operational principles in which both excitation and detection are within the first biological transparent window. A novel and of paramount importance aspect is that the calibration factor can be calculated from the Eu(3+) emission spectrum avoiding the need for new calibration procedures whenever the thermometer operates in different media.