Laishun Qin

Air Atmosphere Annealing Effects on LSO:Ce Crystal

Cerium-doped lutetium oxyorthosilicate Lu2SiO5:Ce crystal is a well-known scintillator with an excellent figure-of-merit. In this paper, air annealing was used to further improve its scintillation properties. The samples cut from Czochralski grown Lu2SiO5:Ce crystals were annealed in air atmosphere at 1400°C for 10 h. Based on the analysis of the difference in the crystals spectra (such as absorption, emission, and thermoluminescence) obtained before and after annealing, we investigate the nature of the observed effects. To investigate the annealing effects on the valence state of cerium ion, synchrotron radiation was used in this work as an energy source to measure the X-ray absorption near edge spectroscopy of cerium ions. It is supposed that annealing in air atmosphere helps to reduce the content of deep traps, which possibly include oxygen vacancy, lower the intensity of afterglow, shorten the decay time of afterglow, and increase the luminescence intensity of Ce2 (6-oxygen-coordinated). However, this may also cause cerium ion to be oxidized to +4 charge state, which may introduce an additional nonradiative trap center, thereby weakening luminescence.

Influence of RE Doping on the Scintillation Properties of LSO Crystals

Rare Earth (RE) such as Y, La, Sc and Gd ions doped Ce:Lu2SiO5 (LSO) crystals, were grown by Czochralski method. The concentrations of these RE ions in LSO crystals were measured, and their segregation coefficients were calculated according to the concentrations. La3+ was found to be helpful to increase the segregation coefficients of Ce3+ in LSO crystals. Transmission, UV and X-ray excited emission spectra, and UV light emission decay curves of RE-doped LSO crystals were tested at room temperature. No significant difference in emission spectra and decay time can be identified among these RE-doped LSO crystals. Doping with La3+ may improve the energy resolution and photoelectron yield of LSO crystals.

Luminescence Properties and Their Temperature Dependence of

Cerium-doped lutetium pyrosilicate (LPS:Ce) crystal with dimension of Φ 10 × 40 mm was grown successfully by Czochralski method. Its crystal structure was determined to be monoclinic with space group of C2/m. The optical transmission, UV and X-ray excited emission spectra, as well as decay curves were measured from 77 K to 500 K. Two emission peaks, 380 nm and 403 nm result from the transition of electrons from 5d1 to two ground levels (2F5/2 and 2F7/2) of Cerium ions (Ce3+) in the LPS:Ce crystals. The decay time of the fluorescence is weakly increasing from 77 K to 400 K and then decreases sharply. The light output of LPS:Ce can be improved greatly by annealing at 1400°C in air. TSL peak at 543 K in LPS:Ce is suggested to be related to oxygen vacancies which are one of the reasons of the poor light output.

{\rm Lu}_{2}{\rm Si}_{2}{\rm O}_{7}:{\rm Ce}

Radiation damage of Lu2SiO5:Ce (LSO:Ce) crystals was investigated through intense UV light. An absorption band at 435 nm was observed in the transmission spectrum of the damaged LSO:Ce crystal, similar to that of absorption band caused by gamma ray irradiation. GDMS analysis for LSO:Ce crystals revealed the existence of impurities, such as Yb in the crystals. The impurities might be responsible for the optical absorption of the color center and the radiation center.