A photoacoustic (PA) spectrum of the f-f transitions in Er 2O3 was recorded at room temperature. The PA spectrum, consisting of many absorption lines in the visible region of the electromagnetic radiation, was compared with the PA spectra of Er-hydrazone and Er-hydrazine complexes. The most intense PA line for erbium organometallic complexes and Er2O3, was observed at 525 nm (5I 15/2 - 2H11/2). The PA spectroscopy showed that the relaxation processes connected with the erbium(III) f-f transitions could strongly depend on the type of the used matrix and on the preparation conditions. The thermal annealing process could influence the creation of different defects which could influence the PA spectra of rare earth(II) ions, especially their relative intensities. The proposed method can be used for characterization of materials by studying the relative intensities of spectral lines produced by the introduction of rare earth(III) ions (with localized wavefunctions) with the PA spectra in the visible region of radiation. © 2010 Advanced Study Center Co. Ltd.