Dielectric Anomalies in Srtio3 at High Electronic Excitation Rates and Cryogenic Temperatures

Ionoluminescence measurements of SrTiO3 were performed from 30-100 K using 3 MeV H+ and 19 MeV Si6+ ionsH. Spectral kinetics curves exhibited sharp qualitative and quantitative changes around 65 K. The behavior of the 2.0 eV emission, associated with VO-T3+ centers, was correlated with the large anomalous increase in electron conductivity at temperatures below 65 K. The center of the band was observed to undergo a shift to higher energies as temperature was lowered. It is proposed that the blue shift may be related to the crossing of soft antiferrodistortive and ferroelectric phonon modes at 65 K. With increasing ion fluence, the intensity of the 2.0 eV band exhibited an initial growth phase, attributed to oxygen vacancy production through elastic ion-atom collisions. It is followed by a decay stage in which irradiation-induced non-radiative recombination sites quench the light emission. Vacancy production cross sections extracted from the data agree quantitatively with binary collision approximation predictions. The intensity of the 2.8 eV band, associated with a self-trapped exciton (STE) excited state, followed Arrhenius behavior below 65 K with an activation energy of 25 meV. The same activation energy was also measured in thermal quenching curves for the 2.0 eV band and 2.5 eV band, associated with the ground state STE. This suggests a possible role that the excited state of the STE plays in thermal quenching. Finally, a splitting of the 1.55 eV emission, associated with Cr3+ impurities, was observed below 90 K under proton irradiation.