Optical and scintillation characteristics of Bridgman LuAP single crystals for positron emission tomography

An efficient growth process is developed employing the vertical Bridgman method, which provides for LuAP single crystals of high optical quality and optimized Ce³⁺ concentration. In order to achieve high light yield and good energy resolution in thick samples, it is necessary to minimize the thickness dependence of the light yield, which is due to color centers degrading optical transparency in the range of Ce³⁺ emission. Earlier unattained optical quality is demonstrated on a series comprising 150 0.2 cm*0.2 cm*0.8 cm scintillation elements with Ce³⁺ concentration in the range 0.23-0.45%, i.e. low underlying absorption (8-12 cm^-1 at 260 nm), high slope of the optical band edge (8.1plusmn0.7 %/nm) and high optical transparency (up to 50% at 335 nm; 80% at 600 nm). For crystals doped with ~0.4% of Ce³⁺ the mean light yield measured in the vertical position is 5670 ph/MeV. The mean ratio of the light yield measured in the vertical and horizontal positions is 64% (73% in the best crystals). The mean intensity of the fast component is 77% with decay time 17.9 ns. The series will be used by working groups of Crystal Clear Collaboration for tests in prototype detector modules