Optical properties and electronic structure of Lu2SiO5 crystals doped with cerium ions: Thermally-activated energy transfer from host to activator

This paper reports on the optical properties of cerium-doped lutetium oxyorthosilicate (LSO:Ce) crystals. The reflection and X-ray photoelectron spectra are measured, and compared to the electronic structure calculated by a discrete variational Xα method. A sharp exciton band originating from O 2p→Lu 5d transition is observed at 7.27 eV at 6 K, with the band-gap energy of 7.52 eV. Luminescence measurements have also been performed in a wide temperature range of 6-300 K. The intensity of Ce luminescence arising from the 5d→4f transition is temperature-independent under the direct excitation of Ce3+ ions, but it is enhanced at around 50 K under the excitation of host LSO crystals. This enhancement is found to anti-correlate with a thermal quenching of the intrinsic luminescence due to self-trapped excitons. The present results provide a piece of evidence that thermally-activated energy transfer from host to activator takes place efficiently in LSO:Ce.