Fluorescent screens for cathode-ray tubes for television and other purposes

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-cadmium 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.