Electroluminescence from light-emitting diodes by using water-dispersed ZnSe nanocrystals and polymer.

Electroluminescence was obtained from an indium-tin-oxide/poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV): ZnSe/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/ 8-tris-hydroxyquinoline (Alq3)/LiF/Al structured device, in which ZnSe nanocrystals were synthesized in aqueous solution by using mercapto-acetate acid as stabilizer. The mechanical, electrical, and optical properties of the device were established. The photoluminescence and electroluminescence spectra changed with the mass ratio of ZnSe to MEH-PPV in the composite. Comparison between the absorption spectra and photoluminescence spectra of the ZnSe nanocrystals and the MEH-PPV thin film exhibited an effective energy transfer from ZnSe nanocrystals to MEH-PPV, which was one reason for the difference between the photoluminescence and electroluminescence spectra of the MEH-PPV: ZnSe composite film. The recombination mechanism of ZnSe nanocrystals under photo excitation and electric injection was investigated with the help of a single layer device structure of indium-tin-oxide/ZnSe/LiF/Al.