The photoacoustic(PA) amplitude and phase spectra of several kinds of
rare earth (RE) complexes are reported and summarized briefly. It is o
bserved that both the amplitude and phase spectra well characterize th
e different energy levels of the RE complexes. The phase angle of the
RE complexes is associated with the relaxation time tau and the optica
l absorption coefficient beta concerning with the pi-pi transition an
d the f-f transitions, respectively. After individual detailed discuss
ion of the phase spectra, a reasonable theoretical consideration is gi
ven to interpret the results.