Screen composition for cathode ray tubes exhibits differential color of emission as a function of beam current variation at a constant accelerating voltage. The screen consists of a mixture of phosphors which emit different hues, have different current saturation values and exhibit a nonlinear current-brightness characteristic

Hilborn, E. H.

English

NASA Technical Reports Server

March 1968	 Brief 68-10056 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Luminescent Screen Composition for Cathode Ray Tubes 
1.0
	 1 W BEAM CURRENT@ 10KV
	
1.0
	 lOW BEAM CURRENT@ 10KV 
0 L.4 
420	 460	 500	 540	 580	 620	 640	 700
	 460	 420	 500	 540	 580	 620	 640	 700 
WAVE LENGTH u	 WAVE LENGTH 
A screen , composition for cathode ray tubes has 
been developed which exhibits differential color of 
emission as a function of beam current variation at a 
constant accelerating voltage. The screen consists of a 
mixture of phosphors which emit different hues, have 
different current saturation values and at least one of 
which exhibits a nonlinear current-brightness charac-
teristic. At low beam current densities, the emission 
color of one of the phosphors predominates. As cur-
rent density is increased, this phosphor reaches satu-
ration,while the brightness of the second phosphor 
continues to increase so as to effectively mask the 
emission color of the first phosphor. 
The lack of emission of this second phosphor at low 
current densities results from the intentional incorpo-
ration of poisoning elements such as nickel, and is 
particularly effective with ZnS:CdS systems. Thus, by 
mixing a nonlinear ZnS:CdS phosphor with any of 
a number of linear phosphors having limited activator
content so that they will saturate at low current values, 
a number of color combinations become possible. 
For example, a nonlinear sulfide green may be 
mixed with a linear red phosphor. When' an electron 
beam of 1.0 microampere per square centimeter at 10 
kilovolts is applied, the red will predominate. On the 
left figure it can be seen that there is relatively little 
green' component and considerable red component, 
as evidenced by the peak in the 640 millimicron range. 
When the electron beam current is increased to 10 
microamperes per sq cm at 10 kilovolts, the red phos-
phor saturates while the green component increases, 
as is evidenced in the right figure where there is now a 
peak in the 520-560 millimicron range, overpowering 
the 640 millimicron peak. 
This arrangement is particularly useful when a dis-
play gradient is' important, as an automatic alert, in 
which displayed values representing normal circum-
stances may be green. As conditions progress from 
(continued overleaf) 
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normal to abnormal, the beam current may be pro-
grammed to lower values so that the Color rendition is 
modified to include overlapping color display, i.e., 
amber. Then, if circumstances become seriously ab-
normal, the beam current may be programmed to even 
lower values so that the red will now predominate, 
providing an immediate alert to the observer. Modu-
lation may also be effected with other phosphor mix-
tures, so that red requires the higher beam current. 
Notes: 
1. This screen would also be useful in multiple gun 
tubes and would obviate the present requirement 
in such tubes of positioning dots of the three addi-
tive primary colors (red, green, and blue). Addi-
tionally, since no registration problems would 
occur, the spacing and diameter of the openings in 
the aperture mask could be made an order of mag-
nitude closer and finer, respectively. In such a tube,
by merely biasing the individual guns to different 
values, the resultant differential beam intensities 
would yield the appropriate colors wherever the in-
dividual beams impinged on the screen. Relative 
brightness of the primaries would be controlled 
by variation in duty cycle. 
2. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Electronics Research Center 
575 Technology Square 
Cambridge, Massachusetts 02139 
Reference: B68-10056 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: Edwin H. Hilborn 
(ERC-19) 
Brief 68-10056	 Category 01


Luminescent screen composition for cathode ray tubes

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