Crystal Growth, Optical, and Scintillation Properties of Eu²+-Doped TlSr₂Br₅

Crystals of undoped and Eu2+-doped TlSr2Br5 of up to 16 mm in diameter and 50 mm in length were grown by the vertical Bridgman technique. TlSr2Br5 has the monoclinic crystal structure with space group P21/c. Its density and $Z_{\text {eff}}$ are 5.03 g/cm3 and 58.6, respectively. Radioluminescence spectra of undoped and Eu2+-doped TlSr2Br5 feature a broad emission band peaking at about 440 nm for undoped and 520 nm for Eu2+-doped crystals. The light yield of undoped TlSr2Br5 is 42000 ph/MeV, which increases to 55000 ph/MeV for Eu2+-doped crystals. The energy resolution at 662 keV (137Cs) is about 5%–6% full-width at half-maximum (FWHM). The scintillation decay of undoped and Eu2+-doped TlSr2Br5 is on the order of hundreds of nanoseconds.