An electroluminescent fluorescent substance, which is composed of electroluminescent fluorescent particles having an average particle diameter of 0.5 μm to 20 μm 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 1×10−4 to 1×10−2 mol/mol and gold 1×10−6 to 5×10−4 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.