Two kinds of europium-substituted Keggin type polyoxometalates of BPOM:Eu and ZrPOM:Eu have been synthesized

which are highly luminescent.Their Keggin type structure has been characterized by IRand XRDspectra.The emission and excitation spectra have been measured at room temperature.The emission spectra show Eu gives strong emission in red light region

but the magnetic dipole transition

5

D

0

→

7

F

1

domains others in BPOM:Eu;while a hypersensitive electric dipole transition

5

D

0

→

7

F

2

domains others in ZrPOM:Eu.The

5

D

0

→

7

F

1

and

5

D

0

→

7

F

2

transitions are extremely sensitive to the chemical surroundings in the vicinity of the Eu

3+

ions.The

5

D

0

→

7

F

2

transition is not only permissive in asymmetry environment but also is of hypersensitive forbidden transition which is extremely sensitive to the chemical surroundings in the vicinity of the Eu

3+

ions.When the Eu

3+

ions’ sites hold asymmetry centers

the

5

D

0

→

7

F

2

transition of Eu

3+

ions is permissive while in symmetrical environment the

5

D

0

→

7

F

1

transition is permissive.Judged from the spectra results the Eu site symmetry in BPOM:Eu surpasses that in ZrPOM:Eu.This contrast stems from different nature (radius and polarative ability) of the boron and zirconium heteroatoms.The site difference also influnce on Eu

3+

ions’ excitation spectra.The spectrum of ZrPOM:Eu has four main groups of peaks:the highest peak laying at 395 nm

the others laying at 381～385 nm

464 and 535 nm with similar intensity.The spectrum of BPOM:Eu has two main groups of peaks:the highest peak lying at 395 nm

the second highest peak laying at 381～385 nm

the others are very weak.There exits energy transfer among Eu

3+

ions.Resonant transfer is important ways for lanthanide especially the same kinds of lanthanide ions due to more spectra overlapping.This function leads to typical fluorescence quenching

the maximum intensity lies at Eu concentration of 2.0% in BPOM:Eu and at Eu concentration of 2.4% in ZrPOM:Eu respectively.There exist two characteristic absorption bands of Keggin anions at nearly 200 and 260 nm in ultraviolet region ascribeed to O

d

→W charge transition.There may exist possibility of energy transfer within short distance.There exists low intramolecular energy transfer from the excited O

d

→W charge transition to Eu

3+

in ZrPOM :Eu

but doesn’t in BPOM:Eu at room temperature.