The absorption spectrum and the energy levels of Eu

3+

of Na

5

Eu(WO

4

)

4

crystal have been determined. The absorption edge lies at 290nm (4.3eV).The branch ratios of fluorescence lines of

5

D

0

to

7

F

1

2

3

4

are 0.041

0.832

0.006 and 0.121

respectively.The strongest fluorescence line(

5

D

0

to

7

F

2

(E)) is 617.2nm

the branch ratio of which is 0.637 and halfwidth is about 1.5nm. And the fluorescence of

5

D

1

and

5

D

2

to

7

F

j

is so weak at room temperature that they have not been observed in our experiment.According to Raman and infrared spectrum analyses

the energies of anti-symmetrical stretching vibration of WO

4

2-

in Na

5

Eu(WO

4

)

4

crystal are very high.It will cause a strong non-radiation transition from

5

D

2

to

5

D

1

and then to

5

D

0

. The lifetime experiment will support this further more.By using a YAG:Nd double frequency pulso laser (530nm

6ns) to excite the Eu

3+

ions from

7

F

0

. to

5

D

1

the strong fluorescence was detected

which only belongs to

5

D

0

→

7

F

j

(j=1

2

3

4)

but not to

5

D

1

→

7

F

j

. It means that an energy transfer from

5

D

1

to

5

D

0

is occured.The growing time of

5

D

0

to

7

F

2

(617.2nm) is 20ns. It indicates that the life time of

5

D

1

is about 20μs

which

is much less than about 1ms

the normal life time of

5

D

1

energy level (such as Eu

3+

doped in Y

2

O

3

Y

2

O

2

S and so on). It is shown that the nonradiation transition probability from

5

D

1

to

5

D

0

is very high. From this experiment

the decay time of

5

D

0

to

7

F

2

was determined to be 1.03ms. This decay time is in the same order of above materials doped with Eu

3+

as an impurity. It is even shown that the concentration of Eu

3+

is very high

but this material has no noticeable concentration quenching effect.Several parameters of Na

5

Eu(WO

4

)

4

are determined. For example

transition probability of

5

D

0

→

7

F

2

is 724s

-1

quantum efficiency of

5

D

0

→

7

F

2

is 0.90 and effective emission cross section of the 617.2nm main peak is l.5×10

-20

cm

2

which is an order of magnitude larger than that in K

5

Eu(MoO

4

)

4

.