Dependence of LiF:Mg,Cu,P (MCP-N) glow curve structure on dopant composition and thermal treatment

In a systematic investigation of the effect of dopant composition on dosimetric characteristics of thermoluminescent LiF:Mg,Cu,P phosphor, 130 samples were prepared with different concentrations of all activators over the following ranges: Mg (0-1.0 mol%), Cu (0-0.5 mol%) and P (0-5.0 mol%). From each material a group of sintered detectors was produced. Parameters describing the shape of the glow curve were analysed after standard annealing at 240 degrees C and after annealing at temperatures up to 400 degrees C. It appears that the amplitude of the main dosimetric peak 4 depends on the concentration of Cu and Mg, showing a distinct maximum for certain concentrations of these dopants. Intensities of high temperature peaks tend to rise with increasing Mg and decreasing Cu concentration. The dependence of the amplitude of peak 4 on P concentration is a step function, rising by an order of magnitude as the amount of P exceeds a threshold value of 0.15 mol%. It appears that copper does not participate in the formation of traps nor of luminescent centres and plays an indirect role, that of inhibiting the growth of high-temperature peaks. Increase of annealing temperatures up to 270 degrees C results in a decrease of the signal from high temperature peaks and in an increase of the main peak intensity (for most combinations of dopant composition). At annealing temperatures above 270 degrees C intensities of all peaks decrease. This thermal susceptibility of LiF:Mg,Cu,P appears to be associated with the instability of Mg-related defects.