Enhanced thermoluminescence of sodium-doped lithium–magnesium fluorophosphate Li9Mg3[PO4]4F3

Abstract

Lithium–magnesium fluorophosphate with the formula Li₉Mg₃[PO₄]₄F₃ has recently been proposed as a new thermoluminescent material capable of storing ionizing radiation energy and emitting photons after additional thermal stimulation. Pure and sodium-doped fluorophosphates were obtained by microwave-assisted synthesis. Using X-ray and neutron diffraction methods, it was shown that sodium occupies only one of the three nonequivalent lithium positions. This conclusion was confirmed by a MAS NMR study and ab initio calculations. A significant increase in the thermoluminescence intensity of sodium-containing fluorophosphates in comparison to the undoped compound was found. Analysis of the kinetic parameters obtained from glow curves showed that they are similar for the undoped and sodium-doped samples. This indicates that the addition of sodium does not result in the emergence of novel types of traps, but rather in a change in their number. The effect of sodium on the formation of intrinsic defects, which can be responsible for the enhanced thermoluminescence, is considered using ab initio modelling.