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Energy transfer between in N , N ′-bis-(1-naphthyl)- N , N ′-diphenyl-1,1′-biphenyl-4-4′-diamine (NPB) and rubrene was investigated. The device ITO/CuPc/NPB:rubrene/blocking layer /Alq/MgAg, in which copper phthalocyanine (CuPc) is used as buffer layer, NPB as the hole transporting layer (HTL), trimer of N -arylbenzimidazoles (TPBi) [or 2–(4–biphenylyl)–5–(4–tertbutylphenyl)–1,2,3–oxadiazole(PBD) or 1,2,4–triazolederivative(TAZ)] as the blocking layer, Tris(8-quinolinolato)aluminum complex (Alq) as electron transporting layers (ETL), can not give white emitting light. White emitting light can be realized in a new device with the structure ITO/CuPc/NPB/blocking layer:rubrene/Alq/MgAg, in which rubrene is doped in blocking layer instead of in NPB. The emission spectrum of this device covers a wide range of visible region and can be adjusted by the concentration of rubrene. The white emitting devices with CIE coordinates x =0.31, y =0.32, maximum luminance 8635 cd/m 2 and luminous efficiency 1.39 Lm/w, were obtained with the blocking layer TPBi doped with 1.5% rubrene.