The results of preparing Zn

x

Cd

1-x

S

y

Se

1-y

;Gu

Br yellow ACEL powder have been reported. In zinc sulphide

the bottom of conduction band lowers down if Cd

2+

are substituted for Zn

2+

the top of valence band arises if Se

2-

are substituted for S

2-

. Such substitutions can change the band gap Eg of ZnS. (1) Se

2-

are substituted for S

2-

partly in ZnS

i.e. Zn (S

Se). Yellow ACEL Zn(S

Se):Cu

Br can be obtained when the proportion of Se is more than 50%. But in this case

the ACEL luminance decreases significantly. It is difficult to make practical display devices from them. (2) Cd

2+

are substituted for Zn

2+

partly in ZnS

i.e.(Zn

Cd)S. If one wants to shift ACEL spectrum of ZnS:Cu to the red by a certain amount

the fraction of Cd necessary to be added to ZnS is less than that of Se. But X-ray analysis of Zn

x

Cd

1-x

S

y

Se

1-y

:Cu

Br shows that aaaaaaaaaaa phase appears in the mixed crystals when

x

<

0.94. Therefore

its ACEL luminance also decreases. It is reasonable to assume that if both Cd

2+

and Se

2-

are added in small amount

the EL spectrum can be shifted to the yellow region without remarkably decreasing the EL intensity.