Role of copper in LiF:Mg,Cu,P thermoluminescent phosphors

LiF:Mg,Cu,P phosphors, which have a very high thermoluminescent (TL) sensitivity, are attractive for low level radiation monitoring. While the roles of Mg- and P- related defects on the TL process in this material are reasonably well understood, the role of the Cu impurity is still unclear. In this research, extended X ray absorption fine structure (EXAFS) studies are used to show that a change in the valence of the copper ion, from Cu+ to Cu2+ occurs upon annealing above 240 degrees C, a change that also occurs at radiation damage levels above 10(4) Gy. The results indicate that the presence of Cu+ ions may be essential for the high TL sensitivity of LiF:Mg,Cu,P, and that a change in the copper valence to Cu2+, a process shown to be only partially reversible, degrades the TL sensitivity. The results further confirm that Cu+ plays a role in the luminescence recombination process in this material.