Blue-emitting ZnS:Ag,Al phosphor with low defect density for high-voltage field emission displays

In recent years, deterioration of luminescence efficiency of blue-emitting ZnS:Ag,Al powder phosphors has been investigated for high-voltage (e.g. 6-10 kV) field emission displays (FEDs). It has been found by cross-sectional transmission electron microscopy (TEM) that the degree of crystallinity of ZnS host crystal within the electron penetration depth (e.g. 300 nm) is one of the important factors in order to obtain ZnS:Ag,Al phosphors having a longer lifetime of luminescence efficiency. Taking the evidence available into account, necessary characteristics for a suitable ZnS:Ag,Al phosphor with a lower defect density, N/sub 0/ are speculated to be the optimum amount of Ag activator and equal mole-fraction of Al coactivator, lower amounts of residual flux impurities, typically chlorine, and smaller atomic-scale surface roughness. Therefore, ZnS:Ag,Al phosphors with a lower N/sub 0/ for FED use compared with a P22B ZnS:Ag,Al(Cl) phosphor for color-TV use have been developed by using a suitable firing method and an additional annealing treatment.