3B SCIENTIFIC PHYSICS U19152 Mode D'emploi page 7

•
Illuminate the phosphors with ultra-violet light
and note that there is no change in current.
Since there is no change in current, it is clear that
the emission from the phosphorous materials is
due to excitation processes and not to ionisation.
5.3 Phosphorescence and quenching
•
Remove all connecting leads from the tube
(refer to fig. 3).
•
Set up a ultra-violet light source so that the
gun side of the screen can be illuminated.
•
Set up a infra-red light source so that the back-
side of the screen can be illuminated.
•
Illuminate the phosphors with ultra-violet light
until the green phosphor has built up to full
intensity.
•
Switch off the ultra-violet light source and
immediately switch on the infra-red light
source.
The phosphorescence of the unprotected half of
the green phosphor is quenched while the other
half remains unaffected.
Fig. 1 Excitation by cathode ray bombardment
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