This letter discusses the optical properties ofCr3+ions in mixed borate crystals with the formulaRX3(BO3)4, whereR3+=Y3+orGd3+andX3+=Al3+orSc3+. Measurements of the optical absorption spectra have been used to estimate the crystal field strengthDqand the Racah parametersBandC. These quantities confirm that inYAl3(BO3)4(YAB) andGdAl3(BO3)4(GAB)Cr3+ions occupy strong crystal field sites2E)<E(4T2)], whereas inYSc3(BO3)4(YSB) andGdSc3(BO3)4(GSB) theCr3+ions occupy weak field sites4T2)<E(2E)]. The consequence is that the fluorescence spectrum ofCr3+:YAB and GAB reveals the sharpRlines at low temperature andRlines plus broadband at 300 K. BothCr3+:YSB and GSB emit into the broadband4T2→4A2transition at all temperatures. The potential of these materials as laser gain media is discussed. ©1995 American Institute of Physics.