The key roles of 4f-level splitting and vibronic coupling in the high-efficiency luminescence of Ce3+ ion in LuAG transparent ceramic phosphors

Abstract

Ce3+ ion-activated lutetium aluminum garnet (LuAG:Ce) polycrystalline transparent ceramics (TCs) were prepared with high-temperature vacuum-sintering technology. The quantum efficiency of the characteristic Ce3+ 5d→4f luminescence of the prepared LuAG:Ce TC phosphor with 0.50at.% Ce sample was measured to be an almost unit. More interestingly, although the acquired low-temperature luminescence spectra still seemingly consist of double broad bands with considerable overlapping, the five major emission lines due to the multiple splittings of 4f shell of Ce3+ are at least unveiled on the basis of theoretical calculations with the semiclassical time-dependent approach of Heller. The pure electronic transition energy and electron-phonon coupling information of each individual emission line are thus determined. The study leads to some important understandings: (i) The 5d→4f transitions of Ce3+ ion are extremely efficient even in the complex polycrystalline environment; (ii) The radiative transitions are much complicated than the commonly understood picture; (iii) As the radiation energy increases, the vibronic coupling characterized by Huang-Rhys factor becomes weaker; Meanwhile, the contribution to the total luminescence tends to increase; (iv) The involved lattice vibration mode could be the low frequency mode of ∼260 cm−1.