Electroluminescence emission spectra

Fig. 4.16. Absorption and normalized electroluminescence emission spectra of 10 xM fluorescein and the polyfluorene pLED, respectively (Prom [25] - Reproduced by permission of The Royal Society of Chemistry)...

Figure 12. Electroluminescence emission spectra of rod-coil copolymers 5 (1%, 5 %, 10 %, and 15 % HPBT 5a, 5b, 5d, and 5e, respectively).

Fig. 30.5 Photoluminescence and electroluminescence emission spectra of hexaphenyl. Absorbance of vacuum-deposited hexaphenyl oriented perpendicular to the substrate (deposition temperature 170°C) and randomly oriented (deposition temperature 25°C).

Fig. 30.6 Photoluminescence excitation (PLexc) and emission spectra, absorbance and electroluminescence emission spectra of m-LPPP.

The EL spectrum has multiple peaks when more than one mode of the cavity overlaps the free-space emission spectrum. It is possible to realize a white LED with a single electroluminescent material such as Alq by employing a two-mode microcavity device structure in which one of the modes is centered near 480 nm and the other near 650 nm. Such an electroluminescence spectrum, for which the CIE coordinates are (0.34, 0.386),13 is shown in Fig. 4.6. The approximate spectrum calculated with Eq. (4) is also shown in Fig. 4.6. With very minor changes in the device design, it is easy to achieve (0,33, 0.33). For comparison, the CIE coordinates of a noncavity Alq LED are (0.39, 0.56). 

The effects produced by a planar microcavity on the electroluminescence characteristics of organic materials have been described. A number of organic and polymeric semiconductors have been employed by various groups in studies on microcavity LEDs. However, for detailed descriptions, three categories of emissive materials have been considered undoped Alq, Alq doped with 0.5% pyrromethene, and Alq+NAPOXA. Alq has a broad free-space emission spectrum spanning the... 

Fig.4. Electroluminescence spectrum (solid line) and fluorescence emission spectrum (dotted line) of 4-amino-1-naphthalenesulfonic acid in aqueous solution (10 M).

Due to the far-blue emission spectrum of oligophenyls, they can be used as blue electroluminescent emitters, but in order to obtain other colors, dopants are needed. 

Other multilayer devices can be constructed from at least two electroluminescent polymers. If carefully chosen, they show light emission from more than one layer, thus broadening the emission spectrum and suggesting how, in principle, to fabricate a white light source. 

Figure 9-12. Absorption (Abs), photoluminescence excitation spectrum (PLCX), pholo-lumincscence (PL), and electroluminescence (EL) emission of mLPPP.

The electroluminescence spectra of the single-layer devices are depicted in Figure 16-40. For all these OPV5s, EL spectra coincided with the solid-state photoluminescence spectra, indicating that the same excited states are involved in both PL and EL. The broad luminescence spectrum for Ooct-OPV5-CN" is attributed to excimer emission (Section 16.3.1.4). 

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