Here's a good reference regarding the frequency of various radiations. Note that beta (electrons) and gamma (photons) radiation can both have x-ray energies. So too can alpha (helium nuclei) but they can't penetrate nearly far enough for x-ray purposes so are not used. Beta is not used for x-ray purposes because although it too can have high enough energies, its penetrating power is also insufficient.
Wikipedia
phosphor entry - contains a long list of various phosphor formulations and their applications, along with other info.
What forumulation they use depends on the average electron's energy when it arrives at the phosphor surface. It is likely that, considering the short distance between emitter tip and phosphor, the electrons will have low energy (probably between 40-150 eV). Thus, expect plasma-type phosphors with similar output spectra and lifetime. Phosphor compounds with lower activation energy tend to be less stable and thus decay quicker.
Here is a very interesting paper, "
Degradation of ZnS:CU,Au,Al phosphor powder and thin films under prolonged electron bombardment" It comes very close to the topic.
In a CRT, electrons are accelerated over quite a distance by high voltage, so have high energies on arrival (15-25 keV) (high enough that by regulation, the glass must be lead-impregnated to reduce beta radiation [this is a bit silly, because x-rays are between 50-200+ keV. CRT beta radiation can't even pass through aluminum foil]).
The reason for the large energy difference between CRT electrons and plasma UV photons is this: the CRT's phosphor is only activated once per frame, and decays to very-low brightness during the remainder of time. Thus it must be very bright when struck by the electron beam, because during the remainder of the frame-time it will receive no energy. Thus its peak to average brightness ratio is large.
So CRTs both require and provide high-energy phosphor targets and the high-energy electrons to activate them, respectively. I assume that higher activation energy means the compounds are more stable to degradation via thermal and other lower-energy initiated processes.
A plasma phosphor's peak brightness is much lower, because the cell is strobed somewhere around 0.2-1000x per frame (depending on requested brightness) using variable-frequency mode pulse width modulation.
Higher-frequency stimulation with lower-energy quanta means the phosphor must be more sensitive to ionization. At the same average brightness as a CRT phosphor, the plasma phosphor receives many more lower-energy quanta over longer periods of time.
This means that unless the duration of post-activation phosphorescence is decreased (ie. very short-persistence forumulation), residual emission will cause motion smearing on bright to dark transitions. In contrast, the CRT phosphor dot has an entire frametime to decay to zero brightness.
This problem has been only partially solved.
