Emission Spectra of LSO and LYSO Crystals Excited by UV Light, X-Ray and $\gamma$ -ray

Because of their high stopping power (X_o = 1.14 cm, R_Moliere = 2.07 cm) and fast (~ 40 ns) bright (4 times of BGO) scintillation, cerium doped lutetium oxyorthosilicate (LSO) and cerium doped lutetium-yttrium oxyorthosilicate (LYSO) crystals have attracted a broad interest in the high energy physics community. This paper presents a comparative study on emission spectra measured for large size BGO, lead tungstate (PbWO₄), LSO and LYSO samples excited by UV light (photo-luminescence) with and without internal absorption, X-ray (X-luminescence) and gamma-ray (radio-luminescence). A red shift was observed between the emission spectra with internal absorption as compared to that without. An additional red shift and a significant red component were observed in the radio-luminescence spectra measured for LSO samples but not LYSO samples, which were disappeared after a gamma-ray irradiation with an accumulated dose of 5 x 10³ rad. This is the only significant difference observed between the large size LSO and LYSO samples. The origin of these red shifts and the consequence to their light output and applications in the high energy and nuclear physics experiments are discussed.