Phosphor having resistance to deterioration caused by ultraviolet rays and gas discharge display device of which image quality is not readily deteriorated over time

A process according manganese-activated zinc silicate phosphor of the present invention meet <β-α≤0.5 and 1.7≤β, where α is a ratio of the number of zinc atoms and the number of silicon atoms 0 phosphor particle surface area, which surface region comprises a particle surface of the phosphor and its vicinity, and β is a ratio of the number of silicon atoms and zinc atoms in the entire phosphor particles.