GaN-based white LEDs are becoming the most promising next generation lighting sources

but the normal encapsulated white LEDs luminous flux declines very quickly.It is very necessary to research on the aging mechanisms of white LEDs luminous efficiency

chromatic properties

and so on.Temperature accelerated aging experiments on two groups of white LEDs have been performed at 80 ℃ and 100 ℃.Both before and after the aging experiments

the current-voltage(

I-V

) curves of the white LEDs were measured.In the tunneling segment

diffusion segment and reversal leakage current segment of the current-voltage(

I-V

) curves

the current was increased

while that of the serial resistance segment was nearly unchanged.The cause of these rises was the increase of the threading dislocation density and that the metal impurities assembled around the screw threading dislocations and moved along them.At the same time

the high-frequency capacitance-voltage(

C

sc

-V

) curves of the virgin white LEDs and the aged ones at different ambient temperature were measured.In the

C

sc

-V

curve

the capacitance decreased in the reversal bias

and it increased in the forward bias.It means that there are some leakage current channels produced by the dislocations.During all the aging time

Chroma parameters were measured every certain hours.The yellow luminescence proportion in the spectrum increased.In the beginning of the aging

the luminous flux decreased slowly

then it decreased rapidly and suddenly.This fact indicated that the accumulation of all degenerating factors could lead to sudden light-off of white LEDs.Finally

by using the Arrhenius relationship

the lifetime of the white LEDs used in our experiments was calculated as 23000 h.