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Proceedings Paper

Blue light-emitting-diodes from poly (N-vinylcarbazole) doped with colloidal quantum dots encapsulated with carbazole terminated ligand: spectroscopic studies and devices
Author(s): A. Khetubol; Y. Firduas; A. Hassinen; S. Van Snick; Z. Hens; W. Dehaen; M. Van der Auweraer
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Paper Abstract

Blue emitting CdSe/ZnS quantum dots (QDs) were encapsulated with the ligand 11-(N-carbazolyl) undecanoic acid (C11). Steady-state photoluminescence (PL) experiments show an enhancement of the QD emission upon the excitation of the carbazole ligand in solution compared to the situation where a solution with the same concentration of QDs capped with oleic acid (OA) were excited at the same wavelength. This suggests energy transfer from the carbazole moiety to the QD cores. When incorporating the QDs in a poly (N-vinylcarbazole) (PVK) matrix, a significant enhancement of the QD emission upon the excitation of PVK was also observed indicating an efficient energy transfer from PVK to the QDs in the case of C11 capped ligands. Confocal microscopy images of the doped PVK films show clearly better miscibility of PVK and QDs capped with C11 compared with those capped with OA. Nanosecond time-resolved PL experiment shows evidence of singlet transfer with Förster resonance energy transfer (FRET) efficiency of 39% for the QDs in solution, while the efficiency of this process amounted to 15.6% for a PVK film doped with 30 wt% of the QDs. The smaller efficiency of the singlet transfer compared to the overall efficiency of energy transfer, suggested by the stationary PL spectra suggests an important role for triplet energy transfer. Electroluminescent devices were prepared with the structure; ITO/PEDOT:PSS/doped PVK with C11 capped QDs/Butyl PBD/Aluminum. Upon applying voltage, the devices show pure blue electroluminescence at low concentration of QDs (10 wt%) with a turn on voltage close to 6V.

Paper Details

Date Published: 1 May 2012
PDF: 11 pages
Proc. SPIE 8424, Nanophotonics IV, 84242W (1 May 2012); doi: 10.1117/12.922545
Show Author Affiliations
A. Khetubol, Katholieke Univ. Leuven (Belgium)
Y. Firduas, Katholieke Univ. Leuven (Belgium)
A. Hassinen, Ghent Univ. (Belgium)
S. Van Snick, Katholieke Univ. Leuven (Belgium)
Z. Hens, Ghent Univ. (Belgium)
W. Dehaen, Katholieke Univ. Leuven (Belgium)
M. Van der Auweraer, Katholieke Univ. Leuven (Belgium)

Published in SPIE Proceedings Vol. 8424:
Nanophotonics IV
David L. Andrews; Jean-Michel Nunzi; Andreas Ostendorf, Editor(s)

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