412 History of Luminescence 



regarded them as elementary particles of matter. As a beam of 

 electrons,'' this radiant matter is now familiar to every user of the 

 cathode ray oscillograph and to everyone who watches a television 

 screen. 



Electrons are highly effective exciters of luminescence. However, 

 in the earliest work on electrical discharge a? vacuo, it is doubtful 

 whether they were responsible for the luminescence of solids. Both 

 Dessaignes (1810) and E, Becquerel (1839) subjected phospho- 

 rescent material to discharges in a vacuum, but the luminous effects 

 observed were mostly due to ultraviolet light. The green cathodo- 

 luminescence of glass previously mentioned would appear to be the 

 first good example. Cathodoluminescence study of other material 

 began in earnest in 1879 with research by Goldstein (1879) , and 

 by Crookes (1879) , both of whom observed the luminescence of 

 various salts placed in evacuated tubes and subjected to " electrical 

 rays " or " molecular shocks." In a short paper Goldstein recorded 

 the luminescence of double salts of platinum, alkaline earth car- 

 bonates, uranium salts, and alkali hydrates. 



It was Crookes who made a really comprehensive study of cathode 

 rays. He not only marshalled the evidence for their particle nature, 

 but paid particular attention to the cathodoluminescence which they 

 excited. He confirmed the fact that English glass containing lead 

 luminesces blue, as contrasted with the green of continental glass,^ 

 and saw the cathodoluminescence of artificial phosphors (CaS and 

 SrS) , uranium glass, and various precious stones, particularly dia- 

 monds. The color of diamond cathodoluminescence might be blue, 

 green, orange, yellow, or red, whereas the ruby emitted a narrow 

 red line at 689 A, which appeared to be identical with the line which 

 E. Becquerel had observed in his phosphoroscope as a result of light 

 excitation of rubies. 



In the last section of his paper, Crookes reported on polarized 

 cathodoluminescence. He wrote: " I have been favored by my friend 

 Prof. Maskelyne with the following notes of results obtained on 

 submitting to the electric discharge various crystals which he has 



® According to Ramsay (1912: 51) , the name " electron " was applied by G. Johnstone 

 Stoney (1826-1911) of Dublin in 1876 to the electricity carried by a single monovalent 

 atom, identical with Thomson's corpuscles. See Stoney in Phil. Mag. (5) 38: 418-420, 

 1894 and W. Ramsay, Elements and electrons, New York, 1912. 



' Crookes found for example that the luminescence of glass becomes fatigued after 

 continued exposure to cathode rays. A region of his glass tube which had been 

 protected by an opaque object in the shape of a cross casting a " shadow " luminesced 

 more brightly than other regions of the tube when the cross was removed. This 

 fatigue phenomenon persisted even after the glass had been fused and allowed to 

 cool. It is generally true that most cathodoluminescent substances cease to luminesce 

 after long exposure to cathode rays. 



