The spectroscopic properties of undoped and Tb3+-doped Na3Ln (BO3)2 (Ln = Y, Gd) have been investigated in the UV-VUV region. The self-trapped excitons (STEs) emission of undoped-Na3Y (BO3)2 (NYB) was observed upon host excitation at low temperature and the emission intensity decreased with the increase of temperature. When Gd3+ was doped in NYB, the emission intensity of STEs was greatly reduced; instead, strong Gd3+ emission appeared. In Na3Gd (BO3)2: Tb3+, host excitation energy was predominantly transferred to Tb3+ through Gd3+ ions. The energy transfer efficiency from Gd3+ to Tb3+ increased with the increase of Tb3+ content. The results indicate that Gd3+ ions play a crucial intermediate role in host sensitization of Tb3+, which will provide some insights for developing new efficient green-emitting VUV-excited phosphors.