The effects of coactivators of the trivalent ions, Y3+, La3+, Al3+, Ga3+ and In3+ on the green luminescence from ZnS:Ce phosphor have been investigated. Y3+, La3+, and Al3+ ions have a large effect on the blueshift from the green luminescence, but Ga3+ and In3+ ions have a small effect. The large blueshift makes a saturated blue luminescence with a peak wavelength of 451 nm and color coordinates of x=0.15 and y=0.09. Cathodoluminescence also shows saturated blue luminescence. The blue luminescence is due to the 5d-4f transition of Ce3+. The origin of the blueshift is discussed in terms of photoluminescence properties and electron density distribution simulated by a first principles calculation. (c) 2007 The Electrochemical Society.