Phosphorescent dyes

FIGURE 3.21 (a) Energy transfer mechanisms of phosphorescent dye as a sensitizer and (b) the EL external efficiency of the DCM2 doped devices. (From Baldo, M.A., Thompson, M.E., and Forrest, S.R., Nature, 403, 750, 2000. With permission.)... 

G. Lei, L. Wang, and Y. Qiu, Blue phosphorescent dye as sensitizer and emitter for white organic light-emitting diodes, Appl. Phys. Lett., 85 5403-5405 (2004). 

Most reported PPLEDs were fabricated by doping a polymer with a phosphorescent dye. However, aggregation and phase separation effects may cause serious problems for device performance and aging. In this section, we describe the very recent progress in intrinsically electrophosphorescent polymers containing triplet-emitting complexes either as pendant substituents or as a part of a backbone. 

F Shen, H Xia, C Zhang, D Lin, X Liu, and Y Ma, Spectral investigation for phosphorescent polymer light-emitting devices with doubly doped phosphorescent dyes, Appl. Phys. Lett., 84 55-57,... 

Y Noh, C Lee, J Kim, and K Yase, Energy transfer and device performance in phosphorescent dye doped polymer light emitting diodes, J. Chem. Phys., 118 2853-2864, 2003. 

Instead of radioactive ink, pens with phosphorescent dyes are avaUahle. Lucher la, Lego T (1989) Anal Biochem 178 327... 

Fig. 33 Current versus voltage characteristics for different doping concentrations of phosphorescent dye 53 in a CBP matrix...

Figure 183 Lifetime (open circles) and EPH quantum efficiency (triangles) of the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum (II) (PtOEP) embedded in an Alq3 matrix as a function of current density. Two filled circles are the lifetimes of the phosphorescence taken at increasing photoexcitation pulse (left 160nJ/cm2 right 16pJ/cm2). The data adapted from Ref. 493a by Kalinowski et al. [304] Copyright 2002 American Physical Society, with permission.

Figure 27-5 The optical system for measurement of PO The optica system for PO2 is based on the ability of O2 to reduce the intensity and lifetime of phosphorescence from a phosphorescent dye that is in contact with the sample. The optica system comprises a green (519-nm peak) light-emitting diode (LED, that emits light, which is reflected by a dichroic mirror onto the PO2 sensor. Because of the phosphorescence, red light (672-nm peak) is emitted back through the dichroic mirror and onto a photodetector. (From Boaith N,Wandrup J, Larsson L, et al. Blood gases and oximetry calibration-free new dry chemistry and optical technology for near-patient testing. Clin Chim Acta 2001 307 225-33.)...

It is not necessary to use only dyes to take advantage of the energy transfer blends of two polymers can also be used as host-guest systems (Lee et al 2002). The guest molecules can be florescent or phosphorescent in nature. However, phosphorescent dyes based on Ir and Pt complexes have provided significantly higher efficiency of OLEDs because of their ability to emit from both singlet and triplet excitons of the host molecule (Kamata et al 2002),... 

Phosphorescent dyes Red 1. Fac-tris(2-phenyl)-bis(2-(2 -benzothienyl)-pyridinato-... 

Table 2. List of various host materials and fluorescent and phosphorescent dyes used for fabrication of WOLED...

In 1998, Baldo et al. [15] showed that the efficiency of organic LEDs can be improved by using phosphorescent dyes. In their device, the phosphorescent oactaethyl-porphine platinum (PtEOP) dye was doped into an appropriate small molecule host at a low concentration. This electrophosphorescent device emitted red light with an external quantum efficiency of 4%. 

This chapter is divided into six sections. Section 11.2 gives a short introduction into the optical and electronic properties of mostly used phosphorescent dyes. In Section 11.3, mechanisms of excitation of these dyes in polymer hosts will be discussed. The optimization of green, red, blue and white devices based on a PVK host is the subject of Section 11.4. The following two sections present selected examples of devices with conjugated polymer hosts or using fully functionalized polymers. Finally, a short conclusion and outlook summarize the current status of phosphorescent polymer LEDs. 

In phosphorescent dyes, strong spin-orbit coupling leads to efficient intersystem crossing of the singlet excited states to the triplet manifold, and also mixes the singlet and triplet excited states, removing the spin-forbidden nature of the radiative transition of the triplet state to the ground state. Various kinds of phosphorescent dyes have been tested in OLEDs. We will focus here on three types of complexes, which are widely studied in OLEDs. 

Transfer Processes in Polymer Hosts Doped with Phosphorescent Dyes... 

---