Deterioration of ZnS-type and Eu3+-activated phosphors for high-voltage field-emission displays

Deterioration of luminescence efficiency η of blue- and green-emitting ZnS-type phosphors, and red-emitting Eu3+-activated phosphors has been studied for high-voltage field emission displays (FEDs). In the blue-emitting ZnS:Ag,Al(Cl) phosphor (P22B and P55) case, the deterioration of η depends mainly on the crystallinity of the host crystal within the electron penetration depth d. It was found that a high-voltage FED tube having a longer lifetime was successfully prepared by using a crystalline-improved ZnS:Ag,Al phosphor. While, in the green-phosphor case, in order to optimize the donor–acceptor (D–A) pair density in ZnS:Cu,Al (P22G) for a suitable color gamut in FEDs, various ZnS:Cu,Al phosphors with low defect density were prepared by using a suitable firing method with a surface treatment like an improved ZnS:Ag,Al phosphor. It was found that the deterioration of improved ZnS:Cu,Al phosphors depends mainly on the D–A pair density in ZnS crystal. Furthermore, in the red-phosphor case, deterioration of Y2O2S:Eu3+ phosphor (P22R) for color-TV has been studied in comparison with a Y2O3:Eu3+(P56) for projection CRTs. It was found that a Y2O2S:Eu3+ phosphor shows a longer luminescence lifetime than a Y2O3:Eu3+ phosphor in high-voltage FEDs. These evidences suggest that the factors influencing the deterioration of luminescence efficiency in ZnS-type and Eu3+-activated phosphors for high-voltage FEDs are the crystallinity of the host crystal, the density of luminescence centers (i.e., susceptibility to the electron irradiation-induced lattice-defects), and the host material (i.e., susceptibility to surface chemical stability).