SPECTRAL STRUCTURE OF THE PHOSPHORESCENCE 

 OF CERTAIN SULPHIDES.^ 



Discussing Measurements by Drs. H. E. Howe, H. L. Howes 

 AND Percy Hodge. 



By EDWARD L. NICHOLS. 

 (Read April 13, 1917.) 



Ph. Lenard, to whom we owe extended studies of the class of 

 highly phosphorescent substances known as the Lenard and Klatt* 

 sulphides, describes^ the spectrum of the emitted light as consisting 

 of a single broad band in the visible spectrum. This band which 

 appears single, in most cases, as viewed with the spectroscope does 

 not however conform to the recognized criteria. The marked dif- 

 ference between the color of fluorescence and that of phosphores- 

 cence and the changes of color during decay, suggest overlapping 

 bands. E. Becquerel* in 1861 showed in his pioneer work on phos- 

 phorescence, that the color of the emitted light varies with the wave- 

 length of the exciting light. His observations apply, it is true, to 

 sulphides of barium, calcium and strontium not identical in make-up 

 with the sulphides of Lenard and Klatt but obviously belonging to 

 the same class. In a recent paper^ the present writer gave more 

 direct evidence of the existence of more than one band in the spectra 

 of these substances. In that investigation which dealt primarily 

 with the phenomena of color as seen in the phosphorescence, it was 

 shown that with the aid of a special form of phosphoroscope*' which 

 permitted of the observation of phosphorescence during the first few 



1 An investigation carried out in part with apparatus purchased by aid 

 of a grant from the Carnegie Institution of Washington. 



2 Lenard and Klatt, Ann. der Physik., XV., p. 225, 1804. 

 3Lertard, Ann. dcr Physik., XXXI., p. 641, 1910. 



* E. Becquerel, La Liimiere, Vol. I., 1861. 



5 Nichols, Proc. Am. Philos. Soc, 55, p. 494, 1916. 



6 Nichols, Proc. Nat. Acad. Sc. II., p. 328, 1916; also Nichols and Howes, 

 Science, N. S., XLIII., p. 937, 1916. 



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