Photoluminescent display devices

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

Photons Photoluminescence Fluorescent lamps, phototherapy lamps, light source, highlighting paints and inks, image intensifier, PLLCD, PDF and other display devices, optically pumped solid-state lasers, up conversion lasers, luminescent solar concentrators, diagnosis... 

Semiconductor quantum dots (QDs) are attracting great interest in applications such as display devices and biochemical fluorescent tag due to their photo stable, size-tunable, narrow bandwidth photoluminescence and chemically functionalizable surfaces[l], QDs also can emit intense light in the region from near-infrared to ultraviolet due to exciton recombination [2,3],... 

In the past, significant attention has been paid to the nanophosphors based photoluminescent as well as displays with improved features of higher resolution, lower dose rates and low voltage electroluminescence operation (10 V). However, the work on the devices is still at laboratory scale and it needs efforts to streamline reliability and reproducibility aspects where by multicoloured displays based on low voltage EL may replace plasma display panels, field emission display devices, etc. in near future. 

It has also been demonstrated that mesoporous materials are viable candidates for optical devices [90]. Silicon nanoclusters were formed inside optically transparent, free-standing, oriented mesoporous silica film by chemical vapor deposition (CVD) of disilane within the spatial confines of the channels. The resulting silicon-silica nanocomposite displayed bright visible photoluminescence and nanosecond lifetimes (Fig. 2.12). The presence of partially polymerized silica channel walls and the retention of the surfactant template within the channels afforded very mild 100-140°C CVD conditions for the formation of... 

Figure 10-14. Inset Photoluminescence spectrum for low excitation pulse energy Ep Main part (a) displays the spectrum for pump pulse energies well below the lasing threshold while (b) shows the spectrum obtained for excitation with a pump energy close to the lasing threshold (c) presents the single mode-lasing spectrum emitted when the device is pumped well above threshold. The dashed lines indicate the zero line which is arbitrarily shifted in case of (b) and (c).

In display applications, fast (video rate) switching of the pixels is required. The intrinsic lifetime of the electroluminescence is the decay time of the photoluminescence i. e. less than a nanosecond. Thus, for pixilated polymer emissive displays, the switching rate is limited only by the RC time constant of the device. For the small pixels of a full-color display, C is sufficiently small that the devices can be switched in times in the nanosecond regime. This fast switching is demonstrated for a single pixel in Fig. 4.19. 

The photoluminescence of polyaniline has been studied as a function of the polymer redox state. It was stated that each of the three PANI species have fluorescent emissions with different quantum yields. When conductive domains are present, the emission fi-om excitons located either inside these domains or near to them is efficiently quenched [40], Organic electroluminescent devices (LED s) are a possible alternative to liquid crystal displays and cathodic tubes, especially for the development of large displays. The principal setup for a polymeric LED is ITO/light-emitting polymer/metal. A thin ITO electrode on a transparent glass or polymeric substrate serves as the anode, while metals such as Al, Ca or Mg are used as cathode materials. After applying an electric field, electrons and holes are injected into the polymer. The formation of e /h" " pairs leads to the emission of photons. One of most important opportunities to follow from the use of poly-... 

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