White LED

Semiconductor-phosphor-based sources, for white LEDs, 14 862 Semiconductor photodetectors,... 

Trichoderma reesi, 12 479, 480 Trichoderma viride, 10 536 Trichothecene mycotoxins, 14 144, 146 Trichromatic sources, for white LEDs, 14 862... 

Genetic Algorithm-Assisted Combinatorial Search for a new Green Phosphor for use in Tricolor White LEDs. 

However, such comparison is a meaningless exercise. A comparison of silicon, sapphire, GaAs, or other established materials, rather than other SiC growth techniques, should occur instead. The blue and white LEDs can, for instance, be made on either sapphire or SiC substrates. From a performance point of view, there appear to be advantages with the SiC substrate but the substrate cost is lower on sapphire, therefore making it the most-used substrate. Granted, once larger substrates of SiC are made available, it is doubtful that the LED cost will be lower on sapphire. 

Fig. 12.22. Emission spectrum of a white LED consisting of a blue LED and yellow emitting YAG Ce.

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). 

White LEDs are typically coated with the YAG Ce phosphor that eauses them to emit a whitish light. The Ce activator in YAG has an overlapping excitation-emission band, making it possible to use a blue LED to excite this phosphor. Indeed, the YAG Ce phosphor is "daylight" excited. That is, it luminesces in sunlight due to the blue radiation present. 

Current phosphor research is aimed at obtaining an improved material for use in producing a white LED. This will make possible LED tiles which can be used in home lighting. 

Figure 1.30 Photovoltammogram of a Cu2ZnSnS4 layer measured in 0.2 M Eu(N03)3 under pulsed illumination from a white LED. The cathodic photoresponse shows that the sample is...

Nishiura, S., Tanabe, S., Fujioka, K., Fujimoto, Y. 2011. Properties of transparent Ce YAG ceramic phosphors for white LED. Optical Materials 33 688-691. 

FIGURE 1.22 LED lighting. Ann Arbor, Michigan, has replaced incandescent streetiights with white LEDs. The city estimates the change will save 100,000 per year and reduce annual greenhouse gas emissions by 267 tons. 

The application of transparent Ce YAG ceramic phosphors for white LED has been reported widely. For instance, the Ce YAG ceramics had a broad emission band peaked at 530 nm due to the 5d-4f transition of Ce " [172]. The transmittances of the samples were 70-87 % at 800 nm. The absorption coefficient and emission intensity of Ce " were increased with increasing sample thickness. Under 465 nm LED excitation, the color coordinates of the Ce YAG ceramics shifted from blue... 

Marin R, Sponchia G, Riello P, Sulcis R, Enrichi F (2012) Photoluminescence properties of YAG Ce, Pr phosphors synthesized via the Pechini method for white LEDs. J Nanoparticle Res 14 1-13... 

A related iridium complex has been used for the decarbo)grlative radical allylation of aminoacids and phenylacetic acids that occurs smoothly at room temperature in the presence of Pd(PPh3)4, irradiating by white LEDs. The proposed scheme (Scheme 6) is based on dual catalysis. Ruthenium tris(phenanthroline) dichloride has been used for visible light catalysis of the mild amidation of ketoacids by ort/zo-substituted anilines using ozygen as terminal oxidant (Scheme 7) ... 

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