Lu co-doped Ce:LiYF4 single crystals with Lu 0, 25, 50, 75 and 100 at% concentrations were grown for the control of mean ionic radius at Y site and the effects on crystal growth, structural phase, crystallinity and segregation were investigated. Lu co-doped Ce 2 at%:LiYF4 single crystals with Lu 0, 25, 50, 75 and 100 at% concentrations were grown by the micro-pulling-down method and while the initial part of Ce:LiYF4 single crystal indicated opaque and milky due to the increase of mean ionic radius at Y site by Ce3+ doping, Lu co-doped crystals had transparency in all part of crystals. All Lu co-doped crystals indicated a single phase in XRD measurements and the lattice parameters were systematically decreased with an increase in Lu concentration. Crystallinity of grown crystals became worse by Lu co-doping and the effective segregation coefficients of Ce3+ ion for Lu co-doped crystals were almost the same, 0.15-0.19. (C) 2011 Elsevier B.V. All rights reserved.