Narrow Bandwidth Luminescence from Blends with Energy Transfer from Semiconducting Conjugated Polymers to Europium Complexes

Abstract

Semiconducting (conjugated) polymers have several properties that are advantageous for photonic applications: they have high fluorescence efficiencies (>60 %), emit at wavelengths that span the entire visible spectrum, are mechanically flexible, and can be deposited as uniform thin films by casting from solution. Since the fabrication of the first polymer light-emitting diode (LED) in 1990, [1] there has been extensive research on polymer LEDs and many improvements have been made. [2±4] Single-color displays fabricated with arrays of polymer LEDs will soon be commercially available. Full color displays will require pure red, green, and blue emission.Obtaining pure emission colors from conjugated polymers or small organic molecules is difficult because their emission spectra typically have a full width at half maximum (FWHM) of 50±200 nm. Efficient, pure red-emitting polymer LEDs are particularly hard to make because the human eye is more sensitive to orange emission than red; if the spectrum falls even slightly in the orange, the perceived color is ªorangish redº. Red LEDs can be made by filtering out orange emission or by using polymers or dyes whose emission starts in the red and extends into the infrared, but these LEDs are inefficient because only part of their emission is useful. In contrast to organic chromophores, rare earth ions have very sharp emission spectra (FWHM < 4 nm). [5] In this paper we show that pure red emission can be achieved in polymer LEDs by transferring energy from blue-emitting conjugated polymers to europium complexes. Similar methods have been used to make red LEDs from small organic molecules. [6±10] We show that blends of Eu complexes in poly[2-(6¢-cyano-6¢-methyl-heptyloxy)-1,4-phenylene] (CN-PPP) have an emission spectral linewidth (FWHM) of only 3.5 nm, a photoluminescence (PL) efficiency of 27 %, and an electroluminescence (EL) efficiency of 1.1 %. These blends could be useful as a source of pure red light for full color displays or for photonic devices that require monochromatic light.To incorporate Eu 3+ into conjugated polymers, we synthesized a family of soluble Eu complexes with b-diketonate ligands, codissolved the complexes and polymers in a solvent, and cast films. We chose b-diketonate ligands because they sensitize Eu 3+ emission. [5,11] The sensitization process is as follows: the ligand absorbs energy, undergoes intersystem crossing into a triplet state, and then transfers its energy to the Eu 3+ ion. [12,13] Thus, the first design rule for making fluorescent Eu complexes is that the triplet level of the ligand must be higher in energy than the emissive level ( 5 D 0 ) of Eu 3+ . A second design rule is imposed by the need for energy transfer from the polymer to the rare earth complex. In order to transfer energy from a conjugated polymer to the ligands of a Eu complex by dipole coupling (Förster transfer), the emission spectrum of the polymer and the absorption spectrum of the ligand must overlap. [14,15] Since the ligands whose triplet level lies above the 5 D 0...

Seven‐Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

“…Various type of lanthanide complexes with photosensitized ligand have been reported. [44][45][46][47][48] Tb(tmh)3(tppo) exhibited excitation peak in UV region ( Figure S3). Luminescent seven-coordinate Eu III complex excited at around 450 nm (visible region) may be ideal phosphor for applications such as LEDs, biomarkers, and chemical sensing devices.…”

The crystal structure of tris(μ2-1,3-bis(4,4,4-Trifluoro-3-oxido-1-(oxo)but-2-en-1-yl)phenyl-/κ4O,O′:O′′,O′′′)-bis(1,2-dimethoxyethane-O,O′)-diterbium(III)

“…β-diketonate ligands have been widely used to construct di erent luminescent lanthanide complexes for high molar absorption coe cients, long luminescent lifetimes, and high luminescence quantum e ciency [4][5][6][7]. Herein, we report the crystal structure of a dinuclear Tb(III) complex with the 1,3-bis(4,4,4-tri uoro-1,3-dioxobutyl)phenyl ligand.…”

Structure and Luminescence Properties of Poly(1-hexyl-3,4-dimethyl-2,5-pyrrolylene)

“…The PL band of PHDP resolved into two components, peaking at 23900(±20) cm , with respect to that of the monomer. The luminescence of PHDP is very comparable with that of poly(N-vinylcarbazole) (PVK), which is widely used as a sensitizer 13 and emitter. 14,15 Like PHDP, PVK in THF excited at UV wavelengths produces blue emission in the 360-500 nm region, as shown in Figure 1.…”