[en] This patent describes an improved brightness oxyhalide phosphor and an X-ray image converter in which the said phosphor converts X radiation to radiation of a longer wavelength with improved image sharpness. The phosphor has the following structured formula: LnOX:Tsub(x) where Ln is one or more of La and Gd, X is one or more of Cl and Br and Tsub(x) is an activator ion selected from Tb and Tm, including mixtures. The recrystallised phosphor crystals have a particle size range of 2-16 microns, are shaped as plate-like particles and have a length to thickness ratio no greater than about 10 to 1. The crystalline characteristics are responsible for the phosphor exhibiting less light scattering and absorption. (Auth.)