The concentration quenching on active ions in laser crystals has effects on their optical and laser properties

so it is necessary to study. Recently

Yb

3+

doped solidstate materials are attractively used as gain media of high efficiency

high power laser with the development of InGaAs laser diode. Among the numerous Yb

3+

doped crystals

Yb: YAG has exhibited enormous potential for high efficiency and high power lasers because of its excellent optical and spectroscopic performances

high thermal conductivity and tensile strength. Since Yb

3+

possesses only two relevant electronic states-the

2

F

7/2

ground state and

2

F

5/2

excited-separated by about 10

000cm

-1

the concentration quenching is nonexistent in Yb: YAG in principle. However

the measurements on fluorescence lifetimes of unannealing Yb: YAG with different doping level demonstrated that there were concentration quenching in Yb: YAG crystal for Yb

3+

doping concen-tration of more than 10at.%. This phenomenon was studied

and the decrease of fluorescence lifetime is attributed to Yb

2+

which results in color center and lattice distortion of Yb: YAG. Trace impurity ions such as Er

3+

and Tm

3+

are detected by means of ICP and X-ray excited emission spectrum

which are also responsible for the concentration quenching at high Yb

3+

doping level. The optimal Yb

3+

doping level in Yb: YAG crystal is less than 20at.%

which is determined by the fluorescence lifetime measurement.