The thin films Y

2

O

3

-ZnS:Mn-Y

2

O

3

give ACEL with brightness as high as 5000 nit but its efficiency is low(10

-3

~10

-4

W/W).The aim of the present work is to find the relation of efficiency of ACEL in ZnS:Mn thin film with the Mn concentration and the origin of concentration quenching.Taking six ZnS:Mn raw materials with Mn concentration varying from 1.5×10

-4

g/g to 5×10

-2

g/g

we evaporate them in vacuum ~10

-5

onto conducting glass to form Y

2

O

3

-ZnS:Mn-Y

2

O

3

ACEL thin film.The Mn concentration in these ZnS:Mn thin films varies only by five times(2.7×10

-5

to 1.3 ×10

-4

g/g).In the range of the Mn concentration from 2.7×10

-5

to 1.3×10

-4

g/g

the efficiency of ACEL increases with the Mn concentration.