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In this work the Bridgman crystal growth and scintillation properties of both undoped and Tl-doped Cs 3 Cu 2 I 5 are presented. This material is very attractive for gamma and X-ray detection applications, with a density of 4.53 g/cm3 and effective atomic number of 51.9. Undoped Cs 3 Cu 2 I 5 had a light yield of 41,500 photons/MeV, with an energy resolution of 4.4% at 662 keV. Thallium doping at 0.5 mol % resulted in a much-improved scintillation response, in which light yield increased to 98,200 photons/MeV and energy resolution reduced to 3.3% at 662 keV. The X-ray excited emission is centered at 442 nm for the undoped and 500 nm for the Tl-doped crystals. The undoped emission is broad, typical of excitonic emission, while thallium doping results in an even broader band with features of both the undoped and thallium defect-mediated emissions. • Transparent single crystals of undoped Cs 3 Cu 2 I 5 and Cs 3 Cu 2 I 5 (Tl) were grown via the Bridgman technique. • Phase purity was established via powder XRD analysis. • Undoped Cs 3 Cu 2 I 5 has 41,500 photons/MeV and 4.4% energy resolution at 662 keV. • Tl doping at 0.5 mol% improves light yield to 98,200 photons/MeV and energy resolution to 3.3%. [ABSTRACT FROM AUTHOR]

KCaI 3 :Eu crystals have been identified as very promising for use in spectroscopic detector applications related to nuclear nonproliferation and domestic security efforts. Initial studies have shown for small crystals a few mm 3 in size with 3% europium dopant concentration, a high light yield of >70,000 ph/MeV and energy resolution of ≈3% at 662 keV is attainable which is comparable with the highest performance scintillators discovered. In this work, single crystals of KCaI 3 with a range of Eu 2+ doping between 0 and 5 at% substituting for Ca 2+ were grown at 22 mm diameter and their performance for gamma-ray spectroscopy studied. Comparisons among crystals approximately Ø22 mm×22 mm (8.4 cm 3 or ≈0.5 in 3 ) provide a more accurate understanding of how scintillation performance changes with Eu doping and increased crystal size. KCaI 3 in the undoped form is shown to be a highly efficient intrinsic scintillator with a defect-related emission at 404 nm which coexists with the Eu 2+ 5d–4f emission in low dopant concentrations and is completely re-absorbed in more heavily doped crystals. For larger crystals, effects from self-absorption due to Eu activation become more evident by a near doubling of decay time for 0.5 in 3 crystals as the activator is increased from 0.5 to 5.0 at% Eu. Comparisons of pulse-height spectra obtained for Ø22 mm×22 mm cylinders with varying Eu concentration suggests best performance is achieved using lower Eu additions closer to 0.5–1.0 at%. Using a modified crystal packaging featuring an offset reflector geometry, 0.5 in 3 crystals of KCaI 3 :Eu can attain under 4% energy resolution at 662 keV. [ABSTRACT FROM AUTHOR]