White light emission from a polymer bilayer by incomplete cascade energy transfer

White light emission was obtained from a light-emitting diodes (LEDs) prepared from an immiscible polymer blend consisting of poly(9,9′-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and poly(2-methoxy-5-(2′-ethy-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV). An inefficient energy transfer between PDHFPPV and MEH-PPV was observed because the blends are partially miscible. More importantly, because the order of bandgap energy is PVK > PDHFPPV > MEH-PPV we observed pure and strong white emission from this PLEDs, which results from the efficient Förster-type energy transfer from PVK to PDHFPPV and the partial energy transfer from PDHFPPV to MEH-PPV. The ITO/(PVK/immiscible blend)/Li:Al devices showed more enhanced white-light output compared with that of the ITO/(immiscible blend)/Li:Al device.