Improved X-ray image intensifying screens comprising rare earth oxyhalide phosphor particles

An X-ray image intensifying screen, which includes in a binder layer rare-earth oxyhalide phosphor particles that are in contact or admixed with an inorganic or organic substance or mixture of substances bringing about that the fluorescence power of said oxyhalide phosphor particles is less prone to be reduced by moisture, said substance being a non-phosphor substance or a phosphor substance other than calcium tungstate and producing hydroxyl ions when put in water, wherein the hydroxyl ion production power of said substance is such that when putting said substance in water at 25 DEG C. in an amount of 0.1 equivalent per liter a pH of at least 8.0 is obtained and the solubility in water of said substance is such that at least 0.05 g of said substance is soluble in 100 ml of water at 20 DEG C.