Green electrophosphorescence from a tetrameric copper (I)amide cluster [CuN(Si(CH3)(3))(2)](4) was successfully observed in the heterostructure device combined with organic carrier transport materials and the copper cluster (peak wavelength = 493 urn, and max. luminance = 400 cdm(-2) at a current density of 177 mA cm(-2) at a drive voltage of 22 V).