Scintillation yield of hot intraband luminescence

Abstract

Cathodoluminescence yield of hot intraband luminescence (IBL) under ∼100 keV pulsed electron excitation was evaluated in several halide and oxide compounds. Its values lie in the range of 5–35 ph/MeV, which is in accordance with the general assumptions on the mechanism of IBL. The expected inverse correlation between the IBL yield and highest phonon energies was found for binary compounds, therefore the IBL yield dependence on charge carrier thermalisation rate was experimentally confirmed. Consequently, CsI was found to have the highest IBL yield (33 ph/MeV) compared to other studied crystals due to its lowest phonon energy among them. The studied sample of pure CsI shows both cathodoluminescence and scintillation yields significantly higher than the value frequently cited earlier (2000 ph/MeV), pointing out that its intrinsic scintillation properties might be currently underestimated. CsI shows good coincidence time resolution (CTR) up to 110 ps FWHM in a TOF-PET-like geometry, which surpasses all the materials studied so far except the much more expensive scintillators from the lutetium-yttrium silicates family (CTR values up to 73 ps). Therefore, CsI can be considered as a promising material for low-cost TOF-PET machines. For complex (ternary) compounds the phonon energies and IBL yield are not noticeably correlated, and the highest spectral yield (at 2.5 eV) among the studied compounds is shown by Na2Mo2O7.