Improved Light Yield and Growth of Large-Volume Ultrafast Single Crystal Scintillators Cs2ZnCl4 and Cs3ZnCl5

Due to their reported fast decay times, Cs2ZnCl4 and Cs3ZnCl5 are promising candidates for detection of gamma rays and X-rays in high count rate and fast timing applications. In this work, we show that single crystals with better optical quality than previously demonstrated - and larger in size - can be grown via the vertical Bridgman method. Highly transparent (sic)7 mm crystals of undoped Cs2ZnCl4 and Cs3ZnCl5 are grown and measured to have light yields surpassing those previously reported, achieving 1980 +/- 100 ph/MeV and 1460 +/- 70 ph/MeV at 662 keV - a 55% and 232% improvement, respectively. We observe single-component scintillation decay times for both Cs2ZnCl4 (1.66 ns) and Cs3ZnCl5 (0.82 ns) and radioluminescence emission with maximum intensity at similar to 290 nm. Scalability of these materials is also evaluated based on growth of (sic)22 mm crystals. Minimal cracking is observed, and the fast decay times are maintained at this size. Coincidence time resolution of 3 x 3 x 5 mm3 and 7 x 7 x 10 mm(3) pixels cut from (sic)22 mm Cs2ZnCl4 are measured to be 148 +/- 1 ps FWHM and 175 +/- 1 ps FWHM, respectively. The improved performance and ability to be fabricated in large sizes now place Cs2ZnCl4 and Cs3ZnCl5 on the map as potential contenders for radiation detection applications where BaF2 - the most commonly used ultrafast inorganic scintillator - is typically considered.