In this paper

the fluorescent properties of Dy

x

Tb

y

Y

1-x-y

P

5

O

14

crystals have been investigated. An important difference with Tb

x

Tb

y

Y

1-x-y

P

5

O

14

crystals is that the

5

D

3

-

7

F

J

transitions of Tb

3+

ions are quenched at low concentration and

5

D

4

-

7

F

J

transitions of Tb3+ ions are sensitized because the Dy

3+

presents in crystals. The reason is that the

5

D

3

-

5

D

4

transition of Tb

3+

and the

6

H

15/2

-

6

H

11/2

transition of Dy

3+

produce the cross relaxation

in addition to the

7

F

8

-

7

F

0

transition of Tb

3+

.We compared the fluorescent intensities between Tb

0.1

Dy

0.1

Y

0.8

P

5

O

14

and Tb

0.1

Dy

0.1

Y

0.9

P

5

O

14

crystals

it was found that the fluorescent intensities of Tb

0.1

Dy

0.1

Y

0.8

P

5

O

14

crystals was much stronger than Tb

0.1

Dy

0.1

Y

0.9

P

5

O

14

crystals in the same condition. When the Tb

3+

concentration is constant

the fluorescent intensities of Tb

3+

decrease with the increase of Dy

3+

concentration