Origin of the discrepancy between photoluminescence brightness of TAG:Ce and electroluminescence brightness of TAG:Ce-based white LED expected from phosphor brightness.

ABSTRACT

A yellow-emitting Tb(3)Al(5)O(12)Ce(3+) (TAGCe) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAGCe showed 90% of the brightness of Y(3)Al(5)O(12)Ce(3+) (YAGCe), it was expected that TAGCe-based WLEDs showed 90% of brightness of YAGCe-based ones. However, the TAGCe-based WLED showed 74% of the brightness of YAGCe-based one. Considering the density and size of the phosphors, the higher density and larger size of TAGCe induced a great deal of sedimentation of TAGCe particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAGCe-based WLED compared to that of the WLED expected from the brightness of TAGCe.