The vacuum-ultraviolet (VUV) spectroscopic properties of undoped and Tb 3+-doped borates Ba 3Ln(BO 3) 3 (Ln = Lu and Gd) with different crystal structures were investigated by using synchrotron radiation. Ba 3Lu(BO 3) 3 (BLB) crystallizes in a hexagonal structure, whereas Ba 3Gd(BO 3) 3 (BGB) crystallizes in a trigonal structure. The maximum host absorption for BLB and BGB was found to locate at ∼179 and ∼195 nm, respectively. Upon host excitation, BLB exhibits an intrinsic broad UV emission centered at 339 nm, which is attributed to the recombination of self-trapped excitons that may presumably be associated with band-gap excitations or molecular transitions within the BO 3 3- group. In contrast to BLB, no broad emission but line emission ascribed to a Gd 3+6P J- 8S 7/2 transition was observed in the emission spectrum of BGB. Upon doping of Tb 3+ ions into the hosts of BLB and BGB, an efficient energy transfer from the host excitations to Tb 3+ via host/Gd 3+ emission was observed, showing that host sensitization of Tb 3+ occurs in these rare-earth borates.