342 History of Luminescence 



light. Goethe (Farhenlehre, 1810) published Seebeck's observa- 

 tions, " Wirking farbiger Beleuchtung auf verscheidene Arten von 

 Leuchtsteine," which stressed the quenching effect of infrared radia- 

 tion on both the Ba sulphide and Sr sulphide phosphors. He used 

 the light transmitted by an orange red glass, which had practically 

 no effect in exciting the phosphorescence of these materials, but 

 when concentrated by a lens on an already luminous phosphor, he 

 found that their phosphorescence, which ordinarily might last for 

 some ten minutes in the dark, disappeared in a few seconds. The 

 date of the experiment is not certain but the striking and well- 

 known quenching effect of long waves on phosphors was certainly 

 recognized about 150 years ago. This quenching results from the 

 increased rate of decay of phosphorescence in infrared light. The 

 luminescence intensity may temporarily increase {Ausleuchtung in 

 German) or may suddenly decrease {Tilgung in German) . If the 

 former occurs, the effect could be called photo-stimulation, analogous 

 to thermostimulation, i. e., thermoluminescence (see Chapter IX) . 

 The rediscovery of the quenching effects of long-wave radiation 

 appears to have been made by E. Becquerel (1843) in 1842 in 

 studying the constitution of the solar spectrum. In 1848 he again 

 called attention to the momentary brighter luminescence of his 

 phosphor where the infrared rays impinged, before the light dis- 

 appeared. So marked is the quenching that dark infrared Fraunhofer 

 lines in the solar spectrum stand out as bright phosphorescent lines 

 against the quenched phosphor, when the sun's spectrum strikes a 

 phosphorescent screen. Quite understandably the effects of long- 

 wave radiation on phosphorescence received considerable attention 

 in the twentieth century, in connection with theories of phospho- 

 rescence. 



Dessaignes, Heinrich and von Grotthus 



In the early nineteenth century extensive investigations ^^ on phos- 

 phors were carried out by Jean Philibert Dessaignes, Placidus Hein- 

 rich (1758-1825), and Theodor von Grotthus (1785-1822). The 

 principal interest of Grotthus was thermoluminescence, but it was 

 becoming obvious that any theory involving light emission from 

 moderate rise of temperature must necessarily explain phospho- 

 rescence as well. Some new phosphors were discovered by these 

 men but at this time the phenomenon of phosphorescence was recog- 

 nized as widespread and a new phosphor did not attract the atten- 

 tion that it would have at the beginning of the eighteenth century. 



*^ A note by L. P. and J. C. Delam^therie (1802) described phosphorescence of cer- 

 tain diamonds and some minerals. 



