Electroluminescence spectra from

Figure 9. Electroluminescence spectra from an n-GaP electrode under about —2.5 V (SCE) in a 0.3M ferro- and ferricyanide solution at pH 13...

Figure 8 (right) Polarised electroluminescence spectra from an ITOtruhhed PPVtPFOl Ca LED. The upper curve is for light emitted with polarisation parallel to the orientation direction and the lower curve for perpendicular polarisation. The anisotropy, IparaUei I perpendicular, hos a peak valuc of 25 1. 

FIGURE 4.5. Electroluminescence spectra from three devices which have different optical thicknesses. The presence of a second mode in one of the spectra is a result of a closer than ideal mode spacing, If the refractive index difference between the materials that constitute the QWS is enhanced, the total optical thickness will be reduced and the mode spacing increased. 

FIGURE 4.12. Electroluminescence spectra from a noncavity LED with an emissive layer consisting of Alq doped with 0.5% pyrromethene. Also shown is the EL spectrum of a LED with an Alq emissive layer. The spectra have been scaled so that the areas are proportional to the measured external quantum efficiencies. 

FIGURE 4.15. Electroluminescence spectra from two noncavity devices with the structure shown in Fig. 4.14b. The thicknesses of the undoped Alq layers in the two devices are 20 nm and 30 nm. 

FIGURE 10.22. Polarized electroluminescence spectra from an aligned ITO/PPV/PFO/Ca LED. The spectra were measured for light polarized parallel (open triangles) and perpendicular (open circles) to the rubbing direction. (From Ref. 35.)... 

Fig. 2.35 Electroluminescence spectra from the same PFB/F8BT bilayer device as in Fig. 2.31 measured at 330 K (a) and 289 K (c) at different voltages. The spectra are not normalized and higher intensity corresponds to higher voltage. The corresponding voltages and current densities are plotted in panels (b) and (c), respectively. The data corresponding to 3.2Vapplied bias are marked with an arrow.

Electroluminescence spectra from P(PV) and two derivatives. After Reference [89], reproduced... 

Figure 8.13 Electroluminescence spectra from ZnO-based LEDs grown by RF sputtering with and without Mgo.1Zno.9O barrier layers measured at an operating current of 40 mA. (After Ref [104].)...

FIGURE 4.3. (a) Schematic structure of a microcavity LED with an Alq emitting layer. The top mirror is the electron-injecting contact and the bottom mirror is a three-period dielectric quarter-wave stack (QWS) with Si02(n = 1.5) and SixNy(n = 2.2). (b) Electroluminescence spectrum from a cavity LED compared with that from a noncavity LED. The noncavity LED possesses the same layer structure as shown in (a), but has no QWS. 

FIGURE 4.8. Electroluminescence spectrum from a three-mode microcavity LED, in which the three peaks are at 488, 543, and 610 nm. The EL spectrum from a noncavity device is shown for comparison. 

Vertical emission can also be achieved by the application of dielectric Bragg mirrors layers, which is in principle the DBR structure applied to the direction of the him normal. Such microcavities have been shown to alter the (electroluminescence spectrum of devices as well as the angular radiation characteristics [200-204], Normally, the angular dependence of the emission from a thin him follows Lambert s law [205]. 

The zone of recombination can be very small as was shown by Aminaka et al. [225] by doping only a thin layer (5 nm) in the device by a red emission material. By observing the ratio of host and dopant emission, the authors were able to show that the recombination zone of the device was as thin as 10 nm. The emitted light is usually coupled out at the substrate side through the transparent anode. As a rule, the electroluminescence spectrum does not differ much from the photoluminescence spectrum. 

The /3-diketonate [Nd(dbm)3bath] (see figs. 41 and 117) has a photoluminescence quantum efficiency of 0.33% in dmso-7r, solution at a 1 mM concentration. It has been introduced as the active 20-nm thick layer into an OLED having an ITO electrode with a sheet resistance of 40 il cm-2, TPD as hole transporting layer with a thickness of 40 nm, and bathocuproine (BCP) (40 nm) as the electron injection and transporting layer (see fig. 117). The electroluminescence spectrum is identical to the photoluminescence emission the luminescence intensity at 1.07 pm versus current density curve deviates from linearity from approximately 10 mA cm-2 on, due to triplet-triplet annihilation. Near-IR electroluminescent efficiency <2el has been determined by comparison with [Eu(dbm)3bath] for which the total photoluminescence quantum yield in dmso-tig at a concentration of 1 mM is Dpi, = 6% upon ligand excitation, while its external electroluminescence efficiency is 0.14% (3.2 cdm-2 at 1 mAcm-2) ... 

Electroluminescence spectrum of an ITO/MA-PF/Al device (solid line), an ITO/DA-PF/Al device and the latter device (dotted line) after 60 min continuous operation under air (electrooxidative (Modified from List, E.J.W., Guntner, R., Scandiucci de Freitas, R, and Scherf, U., Adv. Mater., 14,... 

Figure 8.14 Electroluminescence spectrum measured at room temperature for ZnO-based LED having 7 BeZnO/ZnO QWs in the active layer. The prima spectral emission peak is located near 363 nm and arises from localized-exciton (LE) emissions in the QWs, while the seconda peak centered near 388 nm is from impurity-bound exciton emissions in ZnO. The green band (GB) blueshifts with increasing current injection. (After Ryu et al.)...

Fig. 1. Absorption and photoluminescence dashed line) spectra of a thin film of LPPP 26 and electroluminescence solid line) spectrum of an ITO / LPPP 26 (60 nm) / A1 device (from [50])...

It is worth noting some historical aspects in relation to the instrumentation for observing phosphorescence. Harvey describes in his book that pinhole and the prism setup from Newton were used by Zanotti (1748) and Dessaignes (1811) to study inorganic phosphors, and by Priestley (1767) for the observation of electroluminescence [3], None of them were capable of obtaining a spectrum utilizing Newton s apparatus that is, improved instrumentation was required for further spectroscopic developments. Of practical use for the observation of luminescence were the spectroscopes from Willaston (1802) and Frauenhofer (1814) [13]. 

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