Abstract: The X-ray detection element of an X-ray detector is composed of a fluorescent material having a short afterglow and a high sensitivity to the X-radiation to be detected. For the fluorescent material use is notably made of cerium-activated phosphors such as yttrium phosphors, lanthanum phosphors or lutetium phosphors.

Abstract: Method of preparing a luminescent alkaline earth metal fluorohalide activated by Eu.sup.2+ defined by the formula Me.sub.1-p Eu.sub.p FX (Me=Ba, Sr; X=Cl, Br, I; 0.001.ltoreq.p.ltoreq.0.20). MeF.sub.2 is suspended in water after which 1 mole of MeX.sub.2 per mole of MeF.sub.2 is dissolved in the suspension. The suspension, which may already contain europium, is evaporated to dryness at 50.degree. C. to 250.degree. C. The obtained product is mixed with the additional required amount of europium in the form of a europium halide and then is subjected to at least one temperature treatment at 600.degree. C. to 1000.degree. C. in a weakly reducing atmosphere. The obtained reaction product is subjected, possibly after being ground, to a final heating at 600.degree. C. to 850.degree. C. in an inert or weakly reducing atmosphere.

Abstract: In a luminescent layer which is composed of spatially separated areas for reduction of lateral light dispersion in the layer, this subdivision is realized by provision of a crack structure in the luminescent layer.This crack structure is realized by thermal treatment of a layer which is provided on a substratum, and can be made optimum by an appropriate choice of the layer thickness, so that deposition in a plurality of sublayers can be advantageous. The crack structure can also be caused by a pattern which is provided in the substratum surface or by means of a gauze which serves as a substratum.