Fluorescence phosphorescence devices

Fiber-optic biosensors are analytical devices in which a fiber optic device serves as a transduction element. The usual aim of fiber-optic biosensors is to produce a signal proportional to the concentration of target analyte to which the biological element reacts. Fiber-optic biosensors are based on the transmission of light along silica glass fiber, or POF to the site of analysis. They can be used in combination with different types of spectroscopic technique, e.g. absorption, fluorescence, phosphorescence, or surface plasmon resonance (SPR) (14). 

Finally, white-emitting fluorescent/phosphorescent diodes using a polyfluorene host have been reported by Gong et al. Details about the composition and the performance of these devices are contained in Chapter 4. 

PVK are critical in achieving high efficiency. While conjugated polymers, such as poly(fluorenes) and poly(phenylene-vinylenes), have been used extensively for fluorescence-based devices, they are not as useful for phosphorescence-based devices because they characteristically have low triplet energies. The triplet levels of most conjugated polymers are in the red to near-IR spectral region, and thus efficiently quench phosphorescence from dopants designed to emit in the visible part of the spectrum." ... 

This section covers the background information for OLED devices that applies to both fluorescent and phosphorescent devices. In addition, materials and architectures specific to fluorescent devices are discussed. Phosphorescent structures are described in Section 14.4. 

The triplet-harvesting mechanism was confirmed by efficiency analysis of the BIY device spectra. A blue fluorescent (BE) device was constructed similarly to the BIY except that the phosphorescent emitter was omitted. The blue portion of the spectrum (380-512 nm) of the BE device exhibits 4.9% EQE, indicating very efficient fluorescence. Figure 14.52 shows that devices B Y and BE have nearly identical spectral radiance for the blue component of the electroluminescence. Thus, fluorescence remained the same while the addition of the phosphorescent dopant to the BE device resulted in the appearance... 

Sun, Y., Giebink, N. C., Kanno, H. et al. 2006. Management of singlet and triplet excitons for efficient white organic light-emitting devices. Nature 440 908. Deaton, J. C., Kondakova, M. E., Kondakov, D. Y. et al. 2007. Triplet exciton diffusion in hybrid fluorescent/phosphorescent OLEDs. SID Inti. Symp. Dig. Tech. Papers 38 849. 

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

MA Baldo, ME Thomson, and SR Forrest, High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer, Nature, 403 750-753, 2000. 

As an extension of the fluorescent sensitizer concept, Forrest et al. have applied this approach to phosphorescent OLEDs, in which the sensitizer is a phosphorescent molecule such as Ir(ppy)3 [342]. In their system, CBP was used as the host, the green phosphor Ir(ppy)3 as the sensitizer, and the red fluorescent dye DCM2 as the acceptor. Due to the triplet and the singlet state energy transfer processes, the efficiency of such devices is three times higher than that of fluorescent sensitizer-only doped device. The energy transfer processes are shown in Figure 3.21. 

In their follow-up paper, they also demonstrated 100% efficient energy transfer of both singlet and triplet excited states. The device exhibits peak external efficiency and power efficiency of 25 cd/A and 17 lm/W at 0.01 mA/cm2, respectively [343]. Liu demonstrated a high-efficiency red OLED employing DCJTB as a fluorescent dye doped in TPBI with a green phosphorescent Ir(ppy)3 as a sensitizer. A maximum brightness and luminescent efficiency of... 

S. Liu, J. Feng, and Y. Zhao, Enhanced red emission from fluorescent organic light-emitting devices utilizing a phosphorescent sensitizer, Jpn. J. Appl. Phys., 43 2320-2322 (2004). 

There is no reason why the same principle cannot be applied for light-emitting polymers as host materials to pave a way to high-efficiency solution-processible LEDs. In fact, polymer-based electrophosphorescent LEDs (PPLEDs) based on polymer fluorescent hosts and lanthanide organic complexes have been reported only a year after the phosphorescent OLED was reported [8]. In spite of a relatively limited research activity in PPLEDs, as compared with phosphorescent OLEDs, it is hoped that 100% internal quantum efficiency can also be achieved for polymer LEDs. In this chapter, we will give a brief description of the photophysics beyond the operation of electrophosphorescent devices, followed by the examples of the materials, devices, and processes, experimentally studied in the field till the beginning of 2005. 

S Kan, X Liu, F Shen, J Zhang, Y Ma, Y Wang, and J Shen, Improved efficiency of single-layer polymer light-emitting devices with poly(vinylcarbazole) doubly doped with phosphorescent and fluorescent dyes as the emitting layer, Adv. Funct. Mater., 13 603-608, 2003. 

FIGURE 10.7 Power consumption simulation for a 2.2-in. full-color OLED display using Universal Display s phosphorescent OLEDs, small-molecule fluorescent devices, and polymer OLEDs along with a comparison of the power consumed by an active-matrix liquid crystal display backlight. R G B= 3 6 1, 50% polarizer efficiency, and 30% of pixels lit. (From Mahon, J.K., Adv. Imaging, June, 28, 2003. With permission.)... 

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