New developments in X-ray storage phosphors

We found a significant PSL effect in <f>Eu2+</f>-doped fluorozirconate glasses (ZBLAN) which were additionally doped with <f>Br-</f> or <f>Cl-</f> ions. The PSL is attributed to the characteristic emission of <f>Eu2+</f> present in nano-crystallites of <f>BaBr2</f> or <f>BaCl2</f>, which form in the glass upon annealing. The metastable hexagonal form of <f>BaX2 (X=Br,Cl)</f> is always formed first before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL efficiency of the glass ceramic. However, there is a saturation of the PSL efficiency, which is for <f>Br-</f> doping about 9% and for <f>Cl-</f>-doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most efficient phosphor is about <f>100 nm</f>. [Copyright &y& Elsevier]