Eu

2+

-doped CaSi

2

O

2

N

2

(Ca

1-x

Eu

x

Si

2

O

2

N

2

)has been prepared by solid-state reaction method

and the optical properties of the alkaline-earth silicon-oxynitride phosphor have been investigated.Eu

2+

-doped CaSi

2

O

2

N

2

displayed a single broad emission band peaking at 556~568 nm depending on the europium concentration.The emission bands in the spectra of Eu

2+

-doped CaSi

2

O

2

N

2

were assigned to the allowed transition of Eu

2+

from the lowest crystal field component of 4f

6

5d to 4f

7

ground-state level.It has been demonstrated that the Eu

2+

-doped CaSi

2

O

2

N

2

phosphor absorbs strongly the UV-blue part of the electromagnetic spectrum which makes this material attractive as the conversion phosphor for white light-emitting diodes(LEDs)applications.We have also shown that the optical properties depend greatly on the Eu

2+

concentration.A systema-tic red shift of the emission band is observed as the Eu

2+

concentration increases.The results indicate the photoluminescence properties can be tailored by controlling the Eu

2+

concentration.Moreover

for all samples

starting at low Eu

2+

concentration

the emission intensity rises to a maximum at a Eu

2+

concentration of x=0.06 and falls again when the Eu

2+

concentration continues to increase.This decrease in emission intensity beyond a critical concentration can be explained by concentration quenching

which is mainly caused by the energy transfer between Eu

2+

ions.