The terbium-activated yttrium tantalite ( $\mathrm{YTa}{\mathrm{O}}_4\text{:}{\mathrm{Tb}}^{3+}$ ) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of ${\mathrm{Tb}}^{3+}$ in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The $\mathrm{YTa}{\mathrm{O}}_4\text{:}{\mathrm{Tb}}^{3+}$ phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels.