An electroluminescent fluorescent substance, which is composed of electroluminescent fluorescent particles having an average particle diameter of 0.5 .mu.m to 20 .mu.m and a variation coefficient of particle diameter of 35% or less, and having at least 50% have stacking faults arranged in 10 layers or more at intervals of 5 nm or less, the particles containing copper 1.times.10.sup.-4 to 1.times.10.sup.-2 mol/mol and gold 1.times.10.sup.-6 to 5.times.10.sup.-4 mol/mol, to the particles; a sheet-shaped electroluminescence device, which has the electroluminescent fluorescent substance; and an electroluminescence device system; which utilizes the sheet-shaped electroluminescence device.