An account is given of the principal materials employed for the screens in cathode-ray tubes for television and other purposes.The fluorescent and phosphorescent phenomena displayed by willemite, calcium tungstate and cadmium tungstate, zinc phosphate, and the various preparations of zinc sulphide and zinc-jcadmium sulphide, are dealt with in detail. The method whereby the undesirable phosphorescence displayed by zinc sulphide and zinc-cadmium sulphide has been eliminated is explained.Photometric measurements of the illumination of screens composed of a variety of materials under different conditions of excitation are given. A number of spectrograms are included of the fluorescent light emitted by these substances.The results show that:—(1) Zinc sulphide and zinc-cadmium sulphide are the most suitable substances hitherto developed for fluorescent screens for cathode-ray tubes.(2) A special zinc sulphide, giving approximately white fluorescence, has been obtained.(3) A mixture of zinc sulphide and zinc-cadmium sulphide,giving a brilliant white fluorescence of high intensity, has been prepared.(4) Phosphorescence, when not required, can be entirely eliminated.(5) Zinc sulphide and zinc-cadmium sulphide giving prolonged phosphorescence can be produced, and these compounds find application for special purposes.