Improvement of electroluminescent property of blue LED coated with highly luminescent yellow-emitting phosphors

Abstract

White light-emitting diodes (WLEDs) were fabricated by combining InGaN-based blue light-emitting diodes (LEDs) with highly luminescent Tb(3)Al(5)O(12):Ce(3+) (TAG:Ce), Y(3)Al(5)O(12):Ce(3+) (YAG:Ce), and Sr(3)SiO(5):Eu(2+) (SS:Eu). The TAG:Ce-based WLED showed a color rendering index (R (a) ) of 79 and a luminous efficiency (eta (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 (eta (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.