Efficient white organic light-emitting devices with uncomplicated architectures are fabricated employing phosphorescent platinum(II) complexes containing extended pi-conjugated cyclometalated ligands as a yellow-light source, and fluorescent material 9,10-bis-(beta-naphthyl)-anthrene as a blue-light source. Peak external quantum (power) efficiencies of 11.8% (18.4 lm W-1) are demonstrated (see figure).