Document Type

Dissertation

Publication Date

Fall 8-12-1942

Abstract

A method of investigation was developed whereby the intensity of fluorescence was recorded as the density on a photographic plate; the wave length of the fluorescent light was recorded across the plate; and the wave length of the exciting light was recorded as the distance down on the plate. The method makes use of a monochromator and a spectrograph arranged so that the dispersion of one instrument is at right angles to the dispersion of the other. The visible part of the spectrum from the monochromator was not allowed to fall on the samples. The samples could easily and quickly be placed in position or removed. Thus before making the permanent photographic record, they were accessible to convenient visual observation as to intensity of fluorescence and wave length of ultraviolet producing the fluorescence. Samples were made and examined for the composition range extending from pure CaWO4 to pure PbWO4. Several interesting things were observed: The sum of the fluorescent light of all wave lengths excited by ultraviolet of all wave lengths passed through a broad maximum in the neighborhood of a mole fraction of 0.02 PbW04 as had been reported by other investigators. The sum of the fluorescent light was found to pass through a second maximum near pure PbWO4. It was found that the distribution of fluorescent light in the visible spectrum changes with mole fraction of PbWO4 and also to a less extent with the wave length of exciting light. As the mole fraction of PbW04 is increased, the average wave length of the fluorescent light shifts toward the red— that is, the color changes from blue to a color which is more nearly white. As the wave length of the exciting light is increased, the average wave length of the fluorescence again shifts toward the longer wave lengths. The wave lengths of ultraviolet that excite fluorescence vary with the mole fraction. As the mole fraction of PbWO4 in the samples is increased, longer wave lengths of ultraviolet are able to excite fluorescence. Thus the maximum fluorescence excited by a single wave length is in general not at the same composition as the maximum of total fluorescence. For example, the ultraviolet line at 312 mu does not show a maximum fluorescence at a mole fraction of 0.02 but shows a very strong maximum at a mole fraction of about 0.997 PbWO4. The fluorescence exhibited by samples prepared with a mole fraction of about 0.999 was quite strong both by comparison with samples having a mole fraction of about 0.02 and with the fluorescent powders actually used in fluorescent lights.

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