Luminous efficiency white LEDs

The current-voltage and luminance-voltage characteristics of a state of the art polymer LED [3] are shown in Figure 11-2. The luminance of this device is roughly 650 cd/m2 at 4 V and the luminous efficiency can reach 2 lm/W. This luminance is more than adequate for display purposes. For comparison, the luminance of the white display on a color cathode ray tube is about 500 cd/m2l5J. The luminous efficiency, 2 lm/W, is comparable to other emissive electronic display technologies [5], The device structure of this state of the art LED is similar to the first device although a modified polymer and different metallic contacts are used to improve the efficiency and stability of the diode. Reference [2] provides a review of the history of the development of polymer LEDs. 

Thermal decomposition of the fluoroborate involves losses due to resinification unless the salt is completely dry. 85 g portions of the fluoroborate are placed in a 2-1 flask which is connected by a bent glass wide tube to a 1-1 flask, and the uncondensed vapors of BF3 are led over water the unabsorbed gas is fed into an efficient fume cupboard. The diazonium fluoroborate is heated from above with a luminous Bunsen flame until white fumes of BF3... 

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