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.