Luminescent polymer

We assume that standard Coulomb-correlated models for luminescent polymers [11] properly described the intrachain electronic structure of m-LPPP. In this case intrachain photoexcitation generate singlet excitons with odd parity wavefunctions (Bu), which are responsible for the spontaneous and stimulated emission. Since the pump energy in our experiments is about 0.5 eV larger than the optical ran... 

Modification of the top electrode may also be achieved. This was done by adding a small amount of surfactant, such as an ether phosphate or an ether sulfate, to the spin-coal solution of the luminescent polymer [89[. The lipophobic ether chains segregate at the surface of the (predominantly) hydrocarbon polymer, becoming available for complexation with the aluminum cathode which is deposited on top. Thus, the dipole in the surfactant points away from the electrode and lowers its work function to improve the injection of electrons. 

Polymer laser diodes have been an attractive topic after the discovery of EL in conjugated polymers. Optical lasing in semiconducting luminescent polymer solutions was first... 

The speed of p- and n-type doping and that of p-n junction formation depend on the ionic conductivity of the solid electrolyte. Because of the generally nonpolar characteristics of luminescent polymers like PPV, and the polar characteristics of solid electrolytes, the two components within the electroactive layer will phase separate. Thus, the speed of the electrochemical doping and the local densities of electrochemically generated p- and n-type carriers will depend on the diffusion of the counterions from the electrolyte into the luminescent semiconducting polymer. As a result, the response time and the characteristic performance of the LEC device will highly depend on the ionic conductivity of the solid electrolyte and the morphology and microstructure of the composite. 

H. Liang, J. Yan, and J. Lu, Synthesis and optical characterization of a novel blue luminescent polymer regioregular poly(l-alkoxy-2,4 -m-phenylene vinylene), Synth. Met., 142 143-145, 2004. 

N. Benfaremo, D.J. Sandman, S. Tripathy, J. Kumar, K. Yang, M.F. Rubner, and C. Lyons, Synthesis and characterization of luminescent polymers of distyrylbenzenes with oligo(ethylene glycol) spacers, Macromolecules, 31 3595-3599, 1998. 

Keywords Bead Dye Imaging Luminescence Polymer Sensor... 

Luminescent polymer compositions, ( ), were prepared by Uetani et al. (2) and used as polymer light-emitting devices. 

Initially, interest for NIR emission of lanthanide ions stemmed from the development of optical libers, lasers and amplifiers for telecommunication (Kido and Okamoto, 2002 Kuriki et al., 2002) and there are a wealth of theoretical and technical papers published in this area. Up-conversion processes have also been the subject of intense investigations (Auzel, 2004). These two areas of research and development mostly deal with purely inorganic compounds or, more recently, with luminescent polymers they will not be covered in this chapter, with the exception of the latter, which will be partly described. 

A number of studies have suggested that because the electron transport mobility is lower than that of holes and because there is a higher density of electron traps, true balance has not yet been attained i.e. the device performance is limited by the electron transport [163]. In an attempt to address this problem, the effect of blending electron transport materials into the conjugated luminescent polymer was studied. The best results were obtained with (2-(4-biphenyl)-5-(4-tert-butylphenyl)l,3,4-oxidiazole, Bu-PBD, which was... 

Figure VB-2 Comparison of QEj (EL) (solid dots) with QE ,(PL), both measured under the same conditions for devices with different luminescent polymer thicknesses. Open squares PL efficiency as obtained when the incident light intensity was corrected by directly measuring the sum of unabsorbed and reflected light for each individual device outside of the integrating sphere. Solid x s PL efficiency as obtained when the incident light intensity was corrected by measuring the transmittance and reflectance of EL polymer films of different thickness on the glass substrate, following the procedure of Greenham et al. (Taken from ref 158)...

Devices with luminescent polymer films sandwiched between high and low work function electrodes were originally fabricated to be LEDs. These same devices, however, can be operated as photodetectors or photovoltaic cells. With no externally applied bias, the polymer layer has a built-in electric field, because of the difference in work function of the two electrodes, which tilts the energy bands (Fig. VII-3). When light is absorbed by the polymer, some of the electron-hole pairs that are created are separated by the electric field. The holes are then pushed by the field to one electrode and the electrons are pushed to the other anode. The carriers that reach the electrodes provide a voltage that can either be used as a measure of the light intensity or as a source of energy. 

The methods of synthesis described in Chap. 3 were used to obtain labeled luminescent polymers investigated by the PL method. 

A particularly interesting study that exemplifies the effect of nano-confinement is one where poly(phenylene vinylene) PPV, a luminescent polymer, was incorporated into the channels formed from these polymerized hexagonal phases [78]. These hexagonal PPV nanocomposites exhibited a significant enhancement in the photoluminescence quantum yields, from ca. 25 to 80%. The origin of this enhancement is ascribed to the prevention of the formation of poorly emissive inter-chain excitonic species as a result of the confinement of the PPV chains into well-defined and well-separated nanochannels. An important feature of these nanocomposites was that they could be readily processed into thin films and fibres and, more importantly, macroscopic alignment of the channels encapsulating the PPV chains led to polarized emission [79]. 

The PL quantum yield r)pl. While r]pl of many dyes is close to 100% in solution, in almost all cases that yields drops precipitously as the concentration of the dye increases. This well-known concentration quenching effect is due to the creation of nonradiative decay paths in concentrated solutions and in solid-state. These include nonradiative torsional quenching of the SE,148 fission of SEs to TEs in the case of rubrene (see Sec. 1.2 above), or dissociation of SEs to charge transfer excitons (CTEs), i.e., intermolecular polaron pairs, in most of the luminescent polymers and many small molecular films,20 24 29 32 or other nonradiative quenching of SEs by polarons or trapped charges.25,29 31 32 In view of these numerous nonradiative decay paths, the synthesis of films in which r]PL exceeds 20%, such as in some PPVs,149 exceeds 30%, as in some films of m-LPPP,85 and may be as high as 60%, as in diphenyl substituted polyacetylenes,95 96 is impressive. 

At the ITO interface, various conducting polymers have been introduced between the luminescent polymer and the ITO. These include polyaniline56 and polyethylenedioxythiophene (PEDOT) (Fig. 5.13).37 There are several potential benefits from this approach, including the smoothing out of surface features on the ITO which may lead to short-circuits, the possibility of dopants from the con-... 

Phenylene-based polymers are one of the most important classes of conjugated polymers, and have been the subject of extensive research, in particular as the active materials in light-emitting diodes (LEDs) [1,2] and polymer lasers [3]. These materials have been of particular interest as potential blue emitters in such devices [4], The discovery of stable blue-light emitting materials is a major goal of research into luminescent polymers [5]. Poly(para-phenylene) (PPP, Scheme 1, 1) is a blue emitter [6], but it is insoluble and so films of PPP have to be prepared via precursor routes [7]. Substitution with long alkyl... 

Measuring the steady state optical absorption and emission properties of any luminescent polymer is the most basic but fundamental photophysical measurement we can make. Figure 1 depicts both the absorption and emission spectra for a series of polyfluorene oligomers and poly[9,9-di- -(2-ethylhexyljfluorene] (PF2/6), along with the fully rigid ladder type MeLPPP. 

Rothe C, King S, Monkman A (2006) Long-range resonantly enhanced triplet formation in luminescent polymers doped with iridium complexes. Nat Mater 5(6) 463—466... 

Lee, G.J. Jung, B. Y. Hwangbo, C. K Yoon, J. S. (2002). Photoluminescence characteristics in metal-distributed feedback-mirror microcavity containing luminescent polymer and filler, pn.. Appl. Phys. Vol. 41, p. 5241. 

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