The paper presents the results of a study of the build-up and decay of some 200 samples of silicate, tungstate, molybdate and sulphide phosphors, excited by Bg 2536A radiation. The normal silicates decay at first exponentially, with a time constant of the order of 10<sup>-2</sup> sec. This initial rate is independent of the intensity and the duration of the excitation, and varies little among different samples of a given class (e.g., Zn<sub>2</sub>SiO<sub>4</sub>- Mn). The later decay is slower, and does vary markedly from sample to sample, and depends on the intensity and duration of the excitation. CaWO<sub>4</sub> decays too rapidly to be measured with the apparatus used (<50 microseconds); the decay of MgWO<sub>4</sub> lasts about 2 × 10<sup>-4</sup> sec.; both these tungstates show a very faint long phosphorescence which can be enhanced slightly by addition of impurities. The red luminescence contributed by Sm in these and other “pure” phosphors decays exponentially with a time constant of about 7 × 10<sup>-4</sup> sec. Sulphides have complicated decay characteristics, dependent on the intensity and duration of the excitation. Comparison is made with the results of a study of decay after electron bombardment, and with other published data.
R. P. JOHNSON and W. L. DAVIS, "Luminescence During Intermittent Optical Excitation," J. Opt. Soc. Am. 29, 283-290 (1939)