In many hosts

Eu

3+

can be a fluorescent probe to detect local symmetry and microstructure of rare earth ions in a crystal. (La

1-x

Eu

x

)(BO

2

)

3

has been synthesized by solid state reaction at high temperature

and this paper is to establish the relationship between the spectra of Eu

3+

and the crystal structure of (La

1-x

Eu

x

)(BO

2

)

3

. The polycondensation of [BO

3

] units has been analyzed from infrared spectra

and the results suggests the negative ion units are polymerized into chain structure such as (BO

2

)

n

n

-

among which La

3+

and Eu

3+

are scattered. The crystal structure has been investigated using X-ray powder diffraction

which indicates the sample is monoclinic

with space group being

I

2/a. According to the crystal structure and emission spectra of La(BO

2

)

3

:Eu

3+

the relationship between the luminescent properties and the site symmetry of Eu

3+

in La(BO

2

)

3

has been discussed in detail. For space group

I

2/a

the symmetrically equivalent points of 4a

4b

4c and 4d positions have inverse centers

so their site symmetry is

C

i

but there is no inverse center for 4e and 8f position

and their site symmetries are

C

1 and

C

2 respectively. In La(BO

2

)

3

:Eu

3+

system

5

D

0

7

F

0

transition does not exist

moreover

the emission corresponding to

5

D

0

7

F

1

transition is much more intense than that of

5

D

0

7

F

2

transition

so the Eu

3+

must be located at the site of

C

i symmetry

and the

5

D

0

7

F

2

7

F

3

and

7

F

4

transitions are attributed to a little part of Eu

3+

deviated from inverse centers. In addition

it has been confirmed that adding a certain flux may be of great advantage for the sample to be well crystallized and for Eu

3+

to be located at a site of perfect

C

i symmetry so that 590nm emission corresponding to

5

D

0

7

F

1

transition is greatly intensified. On the other hand

the reason that Eu

3+

gives very intense emission nearby 697nm corresponding to

5

D

0

7

F

4

transition need to be further investigated.