White LEDs fabricated using

In order to demonstrate the potential of these materials, the luminescent performance of the solid form ZnSeS (SFZSS) yellow phosphor crystals were investigated by fabricating a white LED using a blue ( 460 nm) device, as shown in Figure 5. The spectral performance of the white LED shown below was compared to YAG Ce powder phosphor and to our standard ZnSeS Cu,Ag (ZSS) powder phosphor, when pumped by a blue LED operating at -455 nm. The luminescence and colorimetric results from these samples are shown in Figure 6 where the SFZSS phosphor appears to have more favorable properties to YAG Ce compared to powder ZSS phosphor. For example, the peak emission of SFZSS is at 577 nm with a FWHM of -99 ran, and et bits properties much closer to YAG (565-570 nm peak and a FWHM-I2I) nm than the ZSS phosphor with peak luminance at 600 nm and a FWHM-89 nm. When combined with a blue LED, the SFZSS phosphor achieved color chromaticity cordinates CIE (x=0.332, y=0.317) and color temperature CCT=5530 compared to CIE (x=0,318, y=0.226) and CCT=9475 for the ZSS phosphor. On the other hand, the YAG Ce with a blue LED has CIE (x=0.316, y=0.302) and CCT=6595. 

Jordan et al. have developed a white organic LED technology also based on the Alq/TAD system.37 The blue component of the spectrum is augmented by introducing a thin layer of a blue-green emitting material between the Alq and the TAD. The use of a dye-doped Alq layer in the device adds to the red component of the combined emission spectrum. In this manner, efficient (0.7% external quantum efficiency) and bright (4750 Cd/m2) LEDs have been fabricated with emission colors that are close to white. 

Bilayer LEDs with two blue light-emitting materials, PVK and poly(2-do-decyl-p-phenylene) (C120-PPP), can emit blue or white light, depending on the solvent used in the fabrication of the second layer, C120-PPP. 

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