Photoluminescence properties of Jahn-Teller transition-metal ions.

This work investigates the influence of electron-phonon coupling associated with E tensor product of e and T tensor product of e Jahn-Teller (JT) effect in different transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon relaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from the absorption spectrum whether a given JT-TM ion is PL or quenched. The prediction is made on the basis of an adapted Dexter-Klick-Russell parameter for JT systems, defined in terms of spectroscopic parameters through Lambda(JT)=alphaDelta(e)(abs)/E(abs), where Delta(e)(abs) refers to the splitting of the parent octahedral E(g) states by the JT distortion in E tensor product of e (alpha=3/4) or T tensor product of e (alpha=1/4), and E(abs) is the energy of the first absorption band involving electronic transition between E(g) and T(2g). We show that PL in any JT-TM ion occurs whenever Lambda(JT)<0.1 or is quenched if Lambda(JT)>0.2. This result is noteworthy since it allows us to establish structural requirements for the JT-TM ion and the host crystal to be PL. Although PL properties of materials containing TM ions depend on a variety of structural factors such as the electronic configuration, the site symmetry, and the crystal field produced by neighboring atoms, the present model achieves this goal through a simple spectroscopic parameter: Lambda(JT). In this work we correlated the PL properties of different sixfold-coordinated JT systems such as Ti(3+), Cu(2+), Mn(3+), Cr(2+), Fe(2+), Co(3+), and Ni(3+) in halides and oxides with Lambda(JT) obtained from their respective absorption spectra. From this analysis we conclude that depending on the nature of the JT coupling and its strength, PL is either strongly favored or quenched in T tensor product of e while it is mostly quenched in E tensor product of e systems due to the larger JT distortion.