Electron-beam-induced charging of phosphors for low voltage display applications

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Abstract
Shifts of the surface potential were measured for several commercial phosphors by monitoring secondary and Auger electron spectra during electron beam irradiation at energies between 0.5 and 5 keV. The insulating phosphors charge strongly negative above 2 keV, whereas the conductive ones do not. This charging behavior is exaggerated after prolonged beam exposure. Measurements using two coincident electron beams to control the surface potential demonstrate that aging-enhanced surface charging decreases the phosphor cathodoluminescence. The dependence of the phosphor surface potential on the voltage applied to the metal plate on which they are deposited was also determined. These data suggest the presence of substantial space charge in the phosphors, even at low electron beam energies where no beam-induced shifts of the surface potentials are seen. We suggest that the electric fields due to these near-surface space charge regions are crucial in altering secondary emission and in establishing a steady state charge balance in the case where no currents can flow from the irradiated phosphor surface to the conductive backplane.