An elpasolite phosphor is provided corresponding to the general formula: A2−yB1+yMe3+X6:xD wherein: A=a monovalent ion B=a monovalent ion A is different from B Me3+=a trivalent ion D is a dopant X is at least one of F, Cl, Br and I 0≦y≦1 0≦x≦0.2 and wherein said phosphor has a specific gravity (sg)≧4. An elpasolite phosphor corresponding to the general formula above is especially useful in the production of prompt emitting X-ray screens and in the production of X-ray energy storage screens.