An image storage screen or panel, suitable for use in applications related with computed radiography comprises, on a support, a binderless needle-shaped stimulable CsBr:Eu phosphor layer, wherein, besides low amounts of a europium activator or dopant in favor of homogeneous distribution of said activator in the CsBr matrix, presence of well-defined amounts of rubidium halide and cesium chloride in said matrix, and, optionally, further presence of alkali metal, alkaline earth metal and/or metal earth salts, and/or, optionally, other metal salts or oxides, provides a remarkable speed increase, without loss in sharpness.