Eu-doped Li(Ca, Sr)AlF6 [Eu:LiCSAF] single crystals with various Ca/Sr ratios were grown by the micropulling-down method, and their optical and scintillation properties were investigated to reveal the effects of Ca/Sr ratio on optical and scintillation properties of the Eu:LiCSAF single crystals. The Li(Ca-1 x ySrxEuy) AlF6 single crystals could be grown in 0 <= x <= 0.1, 0.5 <= x <= 1.0 and y = 0.02 while the Eu:LiCSAF crystals with x = 0.2, 0.25 and 0.4 included two colquiriite-type phases with different lattice parameters. The Li (Ca-1 x ySrxEuy) AlF6 single crystal with x = 0.25 and y = 0.02 showed the highest light yield under neutron irradiation. (C) 2018 Elsevier B.V. All rights reserved.