LIGHT SOURCES 



Some attempts have been made to produce a light amphfier, using this 

 phenomenon, by placing a light-sensitive photoconductive layer between the 

 conducting glass and the phosphor dielectric layer, but the efficiency of such 



Mica sheet coated with 

 glycerin salt solution 



Phosphor in-^^ 

 castor oil 



Copper block 



(a) 



Glass I Conducting film 



, v.^ vk ■■ ■ . "7^ k'-^ k^^"'.^^ '»^, -t.^ '-v ^, ■ -'^ ^. \ ' J of stannic oxide 



--^ r- ; ^ ' , ,,V ^Phosphor in 



Evaporated aluminium film^ plastic 



(b) 



Figure 28.21(a) Destrian's original electroluminescent cell; 

 (b) A conventional electroluminescent light source 



10 10' 



Voltage 



Figure 28.22 The variation of the mean brightness of an 

 electroluminescent panel with voltage 



amplifiers has so far been poor. Further development of suitable phosphors 

 and rapidly acting photoconductors may improve their performance and 

 also extend their use to infra-red and ultraviolet image-converters. If 

 combined with photoconducting cadmium sulphide an electroluminescent 

 X-ray intensifier may be practicable. 



A bi-stable device using optical feedback has also been described, using a 

 green-sensitive cadmium-sulphide photoconductive crystal and a green 



355 



