diketonate europium(III)

Highly luminescent pure-red emitting fluorinated βdiketonate europium(III) complex for full solutionprocessed OLEDs Joao P. Martinsa,b, Pablo Martín-Ramosa,c, Carmen Coyad,*, Manuela Ramos Silvaa, M. Ermelinda S. Eusebioe, Alicia de Andrésf, Ángel L. Álvarezd and Jesús Martín-Gilg

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CEMDRX, Physics Department, Universidade de Coimbra, Rua Larga, P-3004-516 Coimbra, Portugal. Serviço de Medicina Nuclear, SESARAM E.P.E., Avenida Luís de Camões 57, 9004-514 Funchal, Madeira, Portugal. Higher Technical School of Telecommunications Engineering, Universidad de Valladolid, Campus Miguel Delibes, Paseo Belén 15, 47011 Valladolid, Spain. Escuela Superior de Ciencias Experimentales y Tecnología (ESCET), Universidad Rey Juan Carlos, 28933 Madrid, Spain. *Email: [email protected] Chemistry Department. Faculdade de Ciências e Tecnologia, Universidade de Coimbra, P3004-535 Coimbra, Portugal. Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas (CSIC), Cantoblanco, 28049 Madrid, Spain. Advanced Materials Laboratory, ETSIIAA, Universidad de Valladolid, Avenida de Madrid 44, 34004 Palencia, Spain

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* Corresponding author. Tel.:+34916647470. E-mail address: [email protected].

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Abstract. Current manufacturing technologies for OLEDs involve the use of expensive high vacuum techniques and call for thermal stability requirements which are not fulfilled by many materials. These problems disappear when the OLED films are deposited directly from solution. In this study, we have designed, synthesized and characterized a novel octacoordinated complex, Tris(1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedionate)mono(bathophenanthroline) europium(III), to be used as a “complex-only” emissive layer in wet-processed OLEDs. Upon excitation in the UV region, very efficient energy transfer from the ligands to Eu3+ takes place, giving rise to intense red emission with very high monochromaticity (R=19), both in powder and as a thin film. The decay times of 754 µs (powder) and 620 µs (thin film) are comparable to those of the most efficient Eu3+ β-diketonate complexes reported to date. The same energy transfer leading to saturated red and narrow emission is also observed in the OLED device (glass/ITO/PEDOT:PSS/[Eu(cbtfa)3(bath)]/Ca/Al) when biased at >5.2 V. Its high quantum efficiency (~60%), good thermal stability up to 200ºC and adequate thin film forming properties make this material a promising chromophore for cost-effective OLEDs. Keywords: europium(III), β-diketonate, photoluminescence, electroluminescence, OLED, solution-processed

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1. INTRODUCTION Saturated narrow red-emitting organic light-emitting diodes (OLEDs) from conjugated polymers or small molecules are particularly challenging because their emission spectra typically have full widths at half maximum (FWHM) ranging from 50 to 200 nm. In addition, since the human eye is more sensitive to orange spectral range than to red one, if the emission spectrum falls even slightly in the orange, the perceived color is orangish red. Several strategies have been developed to obtain saturated red emission, such as filtering out orange emission or using polymers or dyes whose emission starts in the red and extends into the infrared, but such approaches lead to inefficient OLEDs in which only part of their luminescence output is useful.

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In contrast to organic chromophores, rare earth (RE) ions have very sharp emission spectra (FWHM