Anomalous temperature dependence of phonons and photoluminescence bands in pyrochlore ErTiO: Signatures of structural deformation at 130K

We report a Raman study of single crystal pyrochlore ErTi O as a function of temperature from 12 to 300K. In addition to the phonons, various photoluminescence (PL) lines of Er in the visible range are also observed. Our Raman data show an anomalous red-shift of two phonons (one at ∼200cm and another at ∼520cm) upon cooling from room temperature which is attributed to phononphonon anharmonic interactions. However, the phonons at ∼310, 330, and 690cm initially show a blue-shift upon cooling from room temperature down to about ∼130K, followed by a red-shift, indicating a structural deformation at 130K. The intensities of the PL bands associated with the transitions between the various levels of the ground state manifold ( I) and the H as well as S excited state manifolds of Er show a change at ∼130K. Moreover, the temperature dependence of the peak position of the two PL bands shows a change in their slope (dω/dT) at ∼130K, thus further strengthening the proposal of a structural deformation. The temperature dependence of the peak positions of the PL bands has been analyzed using the theory of optical dephasing in crystals. © 2011 IOP Publishing Ltd.