Cathodoluminescent phosphors excited at low voltages and high current densities often exhibit brightness saturation due to ground state depletion. A two-level model can be used to show that the luminance and saturation behavior of low voltage phosphors can be greatly improved by choosing phosphors with an activator decay time that is considerably less than the excitation dwell time. This is of considerable importance for field emission displays, where saturation due to ground state depletion has been found to be a factor limiting the achievement of the necessary luminance. Thus, fast activators may overcome ground state depletion and can lead to brighter displays. ©1997 American Institute of Physics.