Improvement of electroluminescent property of blue LED coated with highly luminescent yellow-emitting phosphors
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White light-emitting diodes (WLEDs) were fabricated by combining InGaN-based blue light-emitting diodes (LEDs) with highly luminescent Tb3Al5O12:Ce3+ (TAG:Ce), Y3Al5O12:Ce3+ (YAG:Ce), and Sr3SiO5:Eu2+ (SS:Eu). The TAG:Ce-based WLED showed a color rendering index (R a ) of 79 and a luminous efficiency (η L ) of 34.1 lm/W at 20 mA. The YAG:Ce-based WLED and the SS:Eu-based WLED showed low R a values of 75 and 57 but high luminous efficiency values of 38.9 and 41.3 lm/W at 20 mA, respectively. When a mixture of YAG:Ce and SS:Eu was coated on a blue LED and the resultant WLED operated at 20 mA, the WLED showed a highly bright white light similar to daylight (η L =40.9 lm/W, color temperature T c =5,716 K, and R a =76). Moreover, the WLED showed stable color coordinates against a considerable variation of applied current.
PACS76.30.Kg 78.55.-m 85.60.Jb
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