Abstract: Oxyhalides of lanthanum and gadolinium and coactivated with thulium ion and further containing an impurity ion and a second coactivator selected from praseodymium and neodymium, including mixtures thereof, exhibit reduced quantum noise when employed in X-ray image converter devices. In the preferred embodiments, small but effective amounts of ytterbium ion can also be incorporated into the phosphor material to reduce afterglow and a multilayer X-ray screen construction is disclosed employing the improved phosphors.

Abstract: Rare earth oxyhalide phosphors activated with terbium and/or thulium ion are described exhibiting improved brightness which are particularly useful in x-ray image converter devices by reason of producing less light scattering and absorption as a result of superior crystalline characteristics. A multilayer x-ray screen construction utilizing said phosphor material is also described utilizing said phosphor material which exhibits improved image sharpness and a reduced crossover problem. An improved process for producing said phosphor material is further disclosed wherein the selected oxyhalide is recrystallized in a molten alkali metal halide flux to produce the superior crystalline characteristics.