The systems of CeMgAl

11

O

19

-SrAl

12

O

19

and CeMgAl

12

O

19

-SrMgAl

10

O

17

were studied. In CeMgAl

12

O

19

-SrAl

12

O

19

complete solid solutions were observed and the positions of the lower d-band edge and emission peak of Ce

3+

shifted to higher energy while the cell of the solid solutions contracted as a result of decrease of the parameter a as the concentration of SrAl

12

O

19

increased. Furthermore

both the Nephelauxetic effect and the crystal field intensity of Ce

3+

decreased with increasing SrAl

12

O

19

concentration. Except for 0.9 CeMgAl

12

O

19

-0.1 SrAl

12

O

19

the emission position of Ce

3+

in energy increased linearly with increasing SrAl

12

O

19

content

which could be accounted for by power development fashion of the relation

E

=Q [1-(z/4)

l/z

10

-ar

] (see ref. [6]

). For 0.1 CeMgAl

12

O

19

-0.9 SrAl

12

O

19

the deviation of the emission peak of Ce

3+

from the straight line position could be due to a small Stokes shift for the compound. For CeMgAl

12

O

19

-SrMgAl

10

O

17

solid solutions were observed only when SrMgAl

10

O

17

content was within 70%.In the solid solutions

the emission peak energy of Ce

3+

increased linearly

and the cell parameters a and c decreased and increased respectively with increasing SrMgAl

10

O

17

concentration. For 0.1 CeMgAl

12

O

19

-0.9 SrMgAl

10

O

17

two phases were found with SrMgAl

10

O

17

as the primary phase and a magnetoplumbite-type Ce-and Si-double hexaluminate as the second phase

The emission of Ce

3+

in the mixed phases originated probably from the latter compound.The intensity of Ce

3+

emission in solid solutions was considerably enhanced by adding H

3

BO

3

to starting materials. But the Ce

3+

emission would reversely decrease if the quantity of H

3

BO

3

was too high. It was found that the change of crystal habit of solid solutions by H

3

BO

3

and the substitution of B for Al in the compounds were responsible for the observations.