This paper deals with the investigation on the deterioration of powder ACEL phosphor using ion probe experiment.lt is found for the first time that copper ions migrate during the deterioration.This conclusion is in accordance with positron annihilation lifetime spectrum.It is also shown that the degree of copper ion migration was alleviated for annealed and quenched phosphor.The initial brightness of ACEL sample was 450cd/m

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under the excitation of 5kHz and 200 V. It decreased to 125.5cd/m

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after the aging of 4000 hours.The maximum of initial brightness for samples with improved phosphor is 766cd/m

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.