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The phosphorescent decay of Srs.CeSm Hamilton, Donald Ross

Abstract

The general characteristics of infrared sensitive phosphors are discussed, with particular emphasis on SrS. CeSm, known as Standard VII, which is the subject of this research. The apparatus is described, and consists of an infrared spectrometer, a photomultiplier and a direct coupled amplifier. The performance is discussed in some detail. Curves of the decay of phosphorescence for Standard VII are described; it is found that on a log-time log-brightness plot, these curves are straight lines for times greater than ten minutes. The limiting slope depends on the time of excitation, and is related to it by a simple law. It is also established that there are two types of colour centers active during phosphorescent decay, cerium and samarium. The emission of cerium is a band with peak at .485 microns, and that of samarium a series of lines in the red. A number of simplified theories are developed or described, no one of which exactly fit the data. It is suggested that the curves can probably be fitted by an exponential distribution of shallow traps if absorption and scattering are considered.

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