Efficient Visible-Light-Excitable Eu3+ Complexes for Red Organic Light-Emitting Diodes

abstract

Visible-light-excited Eu3+ complexes have received much attention in the last years due to the rapidly increasing demand for less-harmful biomarkers and low-voltage driven emitters in optoelectronics. Nevertheless, these complexes usually exhibit poor emission quantum yields, contrarily to the ones excited in the ultraviolet spectral region. To address this challenge, a series of complexes based on trivalent lanthanide ions, [Eu(bpyO2)(CH3OH)(2)(H2O)(NO3)(2)](NO3) (1), [Gd(bpyO2)(H2O)(4)(Cl)(2)]Cl (4), Ln(tta)(3)(H2O)(C2H5OH) {Ln = Eu (2), Gd (5)} and Ln(tta)(3)(bpyO2) {Ln = Eu (3), Gd (6)}, were synthesized using 2-thenoyltrifluoroacetone (Htta) as primary ligand and 2,2'-dipyridyl N,N'-dioxide (bpyO2) as neutral donor, and characterized, with special emphasis on their crystal structures and luminescence properties. Single crystal X-ray diffraction revealed that the central metal ion has a coordination number of 9 in 1, and 8 in all other complexes. Complex 3 exhibited a broad excitation spectrum ranging from 250 to 480 nm, exhibiting, when compared to 1 and 2, higher absolute emission quantum yields of 0.46, 0.36 and 0.33, for excitation at 400, 425, and 450 nm, respectively. The theoretical intensity parameters, radiative and non-radiative decay rates, and intrinsic and absolute emission quantum yields were assessed using the LUMPAC software displaying a very good accord with the experimental values. Moreover, organic light-emitting diodes with a maximum efficiency of 5.7 x 10(-2) cd A(-1) at 14 V were fabricated using 3 as an emitting layer.

keywords

BETA-DIKETONATE COMPLEXES; LUMINESCENT LANTHANIDE COMPLEXES; INTRAMOLECULAR ENERGY-TRANSFER; EMISSION QUANTUM YIELD; RADIATIVE LIFETIME; INORGANIC HYBRIDS; LIGAND; EUROPIUM(III); SENSITIZATION; OXIDE

subject category

Chemistry

authors

Francis, B; Nolasco, MM; Brandao, P; Ferreira, RAS; Carvalho, RS; Cremona, M; Carlos, LD

Groups

1 - inorganic functional nanomaterials and organic-inorganic hybrids
6 - computer simulation and multiscale modeling

Projects

Díodos emissores de luz (LEDs) branca, inovadores, sintonizáveis e sustentáveis (WINLEDs)

SusPhotoSolutions - Soluções Fotovoltaicas Sustentáveis (SUSPHOTOSOLUTIONS)

Projeto de Investigação Exploratória: Mariela Nolasco (IF/01468/2015)

acknowledgements

This work was partially developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by Portuguese funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. Financial support from FCT (WinLED project POCI-01-0145-FEDER-030351 and SusPhotoSolutions, CENTRO-01-0145-FEDER-000005 funded by FEDER, through POCI and by national funds, OE, through FCT/MCTES) is also acknowledged.. Brazilian funding was provided by CNPq, CAPES, FAPERJ, FINEP, and INEO-MCT. B. F. and R. S. C. thank SusPhotoSolutions and CAPES for their postdoctoral grants, respectively. FCT is also acknowledged for the research contract under the program Investigator 2015 to M. M. N. (IF/01468/2015).