Dlc Electroluminescence

Amorphous diamond coated PET, replacing silver grease, was used as the electrode for the light panel based on electro-luminescence. The result indicated that the brightness of the phosphors increased substantially than conventional EL. Moreover, the decay rate of the illumination was greatly reduced (Sea-Fue Wang, personal communications). In a previous study, the brightness of DEL was shown to increase linearly with the increase of the applied voltage, frequency of the alternative current, and the increase of temperature. The improvement of DEL over EL was like due to the increased voltage in amorphous diamond compared to metal conductor under the same externally applied electrical field.

Because amorphous diamond electrons are bound loosely, they can be free with the input of low amount of energy (e.g. external filed). Consequently, under the external field of alternative current, higher concentration of electrons could be generated momentarily. The fast accumulation of free electrons in amorphous diamond was demonstrated in the rapid saturation of electrons when an external bias of direct current was applied. This phenomenon made amorphous diamond highly useful as the energy storage device (e.g. a high density capacitor). The enhanced capacitance

Figure 9.8. The cooling of LED junction temperature by coating amorphous diamond on the surface of its aluminum substrate heat spreader.

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Current (mA)

Figure 9.8. The cooling of LED junction temperature by coating amorphous diamond on the surface of its aluminum substrate heat spreader.

Figure 9.9. The dramatic cooling effect of high bright LED that was operated at 350 mA by replacing the oxidized layer of the silicon submount with DLC coating.

on amorphous diamond apparently made the DEL brighter than EL that used metal conductors. Because the electrical current was not increased in DEL, the likelihood of thermal damage due to the local current concentration of electricity on phosphor particles can be reduced. This explained why DEL's light faded away much slower than conventional EL devices. EL is a low cost illuminator that can be applied to large area. Unfortunately, its brightness has been low (e.g. < 3000 cd/m2), and the service life has been low (e.g. 2000 h). DEL can overcome the limitation of EL, and hence it can be an alternative to backlighting or for generally illumination (Fig. 9.10).

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