12-9] 



SPECIAL DISPLAY DEVICES 



667 



consideration in generating light. The thickness of the material, which is 

 a few thousandths of an inch, is limited by pinholes and nonuniformities. 

 It is necessary to limit the thickness of the material to prevent dielectric 

 breakdown. Of course, an increase in thickness of material means the 

 application of a higher voltage to obtain the same electrical field intensity. 

 Since there is more phosphor in the thicker material, there will be more 

 light emitted. 



Electroluminescent material emits light as a function of magnitude and 

 frequency of an electrical field. The electroluminescent display device 

 therefore must make use of controlling elements to vary the light intensity 

 of each point of the luminescent material. Variation of the light intensity 

 is of interest to us in two ways — first as a light amplifier and second as a 

 display device. 



Light amplifiers or image intensifiers are of interest to us because of their 

 ability to improve the brightness of our presentation. They are also a first 

 step toward a highly sophisticated solid-state presentation device. 



The first light amplifier was a single-layer type. This single-layer type 

 is excited by the direct action of incident radiation such as ultraviolet or 

 X-rays. Destriau^^ first showed that an a-c field applied across a photo- 

 luminescent phosphor screen would change the light level of the screen. 

 If the exciting radiation were ultraviolet rather than visible light then the 

 light output caused by the electrical field dropped by 50 per cent. D. A. 

 Cusano^^ applied a d-c voltage rather than an a-c voltage and with ultra- 

 violet radiation demonstrated a light enhancement of about 60 times. 

 Fig. 12-42 illustrates the Cusano cell. The Cusano image intensifier has a 

 thin manganese-activated zinc phosphor (10 microns thick) which is vapor 

 deposited. It has extremely high resolution and a capability of reproducing 



Transparent Coating (NESA) 



*-Ob]ect 



DC Voltage 

 Fig. 12-42 The Cusano Light Amplifier. 



i^G. Destriau and H. F. Ivey, "Electroluminescence and Related Topics," Proc. IRE 43 

 No. 12 (Dec. 1955). 



i^D. A. Cusano, "Field Enhanced Solid-State Luminescence," referenced in Phys. Rev. 98 

 No. 4 (May 1955). 



