Scintillation light emission studies of LSO scintillators

UV and gamma-ray excited luminescence and nuclear spectroscopy were used to study the relationship between the scintillation mechanisms of LSO and the spectroscopic characteristics obtained with PMT and APD readouts at room t emperature. No correlation was found between scintillation decay time and l ight output. Like other investigators, we observed the existence of two dis tinct luminescence centers, Ce1 and Ce2, that mainly give rise to short (42 0 nm) and long (440 nm) emission wavelengths. Our measurements showed that different LSO crystals excited by gamma-rays have emission spectra with lar gely different shapes and maxima depending on the relative population and l uminescence efficiency of these centers. It was also found that the poor en ergy resolution of LSO and YSO. scintillators is well correlated with the c oexistence of the two competing luminescence mechanisms. The prevalence of either Ce1 or Ce2 luminescence tends to reduce the variance of light emissi on and, thus, to improve energy resolution. Inversely, the coexistence of t he two centers increases variance and degrades energy resolution.