Pure green and narrow bandwidth emission from organic bilayer electroluminescent devices were presented by using Tb3+∶(SA)3 as hole-transporting layer and emissive layer, and high fluorescent material Alq3 acting as electron-transporting layer. It proves that the emission comes from carriers' recombination after their tunneling through the inner interface (Tb3+∶(SA)3/Alq3) in the bilayer ITO/Tb3+∶(SA)3(40nm)/Alq3(55 nm)/Al diode. The spectrum of the bilayer devices varies with the thickness of the electron-transporting layer. Keeping the thickness of Tb3+∶(SA)3 layer constant, there is no emission from Alq3 layer when Alq3 layer reduces to 12 nm; meanwhile, pure green and narrow bandwidth emission can be observed. Thus, it provides a simple way to obtain high luminance and long-term stability by reducing electron- or hole-transporting layer, especially, by using a lanthanide complex for emissive layer.