Single crystals of U3+ diluted into a matrix of RbY2Cl7 have been grown by the Bridgman-Stockbarger method. There are two different intrinsic U3+ sites in this crystalline host, each with an approximate C-2 upsilon Site symmetry. A third minor U3+ Site was also found. Absorption, fluorescence, and excitation spectra of these crystals were obtained at 300 and 4.2 K. Transitions belonging to each U3+ Site were distinguished by time-gated site-selective spectroscopy. The energy levels of the two intrinsic sites were assigned and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for a 5f(3) ion at a C-2 upsilon symmetry site. Quite different F-4(9/2) fluorescence lifetimes were measured for the three sites, due to a multiphonon decay mechanism which is affected by differences in their respective crystal-field strengths. These results are analyzed quantitatively using tile theory for the electron-phonon interaction.