An electroluminescent phosphor comprising ZnS-based phosphor core particles and a coating layer provided on the individual core particles, the core particles having a mean particle size of 0.1 to 15 .mu.m with a coefficient of variation of particle size distribution less than 35% and containing at least 30%, based on total particles, of particles having at least 10 stacking faults with an interplanar spacing of 5 nm or less.