Vibronic Structure in Luminescence Spectra of Rare Earth Ions In SrTiO3, BaTiO3 and Other Perovskites

In the luminescence spectra of Eu 3+ in SrTiO 3 , two kinds of vibronic structure, i.e. , rather sharp satellite lines (vibronic lines) and asymmetric bands (vibronic tails), were found to exist. The tails were observed also in the spectra of Tb 3+ and Pr 3+ in SrTiO 3 . The tail strongly appears associated only with transitions allowed by forccd electric dipole. A comparison of the luminescence spectra of Eu 3+ in SrTiO 3 and BaTiO 3 has suggested the existence of a correlation between the strength of vibronic structure and the site symmetry of rare earth ions. To investigate this, the luminescence spectra of Eu 3+ were studied in various perovskite type oxides in which the site symmetry of Eu 3+ varies from O h to very low symmetries. It has been clarified that the vibronic lines strongly appear when the site symmetry is O h or very close to it. However, the vibronic tail was observed only in SrTiO 3 . In order that the vibronic tail appears, some special properties of host material seem to be required.