Synthesis And Luminescence Properties Of Rare Earth Eu³⁺-doped Ce₂LnO_5.5?Ln=La,Lu? Phosphor Nanopowders

Over the past few decades,the inorganic luminescent materials have attracted much attention as practical applications in almost all devices for artificial light production.In particular,the rare earth-doped oxides have emerged as a new class of luminescence materials due to its distinctive optical properties,such as a long fluorescent lifetime,large Stokes shift,high stability,high luminescence efficiency and tunable emission colors.Among the rare earth activators,the engineering of Eu³⁺ has been given intensive interests because of its characteristic narrow band red-light emission.CeO₂ compounds have been widely investigated as important functional materials with a cubic fluorite structure.Eu³⁺ ions activated CeO₂ could generate characteristic red-light emission of Eu³⁺ ions under the excitation of 360³70 nm UV ray.However,the luminescence intensity of CeO₂: Eu³⁺ is not high as excited with 466 nm.In this paper,the Ce₂LnO_5.5?Ln=La,Lu?composite and rare earth Eu³⁺-doped Ce₂LnO_5.5?Ln=La,Lu?nanopowders were synthesized with a simple solution combustion reaction.The influences of Eu³⁺ substituting Ln³⁺(Ln³⁺=La³⁺,Lu³⁺or Ce⁴⁺on crystal structures,luminescent properties and fluorescent lifetime of nanopowders were investigated.The X-ray diffraction patterns suggested Ce₂LnO_5.5?Ln=La,Lu?with a cubic fluorite structure which was the same as pure CeO₂ except for the lattice parameter a.After the activator Eu³⁺ was doped to the composite,the Eu³⁺ could locate in either Ln³⁺(Ln³⁺=La³⁺,Lu³⁺)or Ce⁴⁺ sites due to their close ionic radius.It was found that the lattice parameter a was gradually decreased with the increasing Eu concentration as Eu³⁺ occupied La³⁺ site in the Ce₂LaO_5.5: Eu³⁺.On the contrary,the lattice parameter a was obviously enlarged with the increasing Eu concentration if Eu³⁺ occupied Ce⁴⁺ site.In Ce₂LuO_5.5: Eu³⁺,the lattice parameter a was gradually increased with the increasing Eu concentration as Eu³⁺ occupied Lu³⁺ or Ce⁴⁺ site.However,the lattice parameter a was remarkably enlarged as Eu³⁺ occupied Lu³⁺ site rather than Ce⁴⁺ site.All of the phosphor powders showed red-light emission from the dominant ⁵D₀?⁷F₂ characteristic transition of Eu³⁺ under the excitation with 466 nm blue light,and the luminescence of the composite was higher than that of CeO₂:Eu³⁺.In particular,the system displayed remarkably enhanced luminescence as Eu³⁺ occupied Ce⁴⁺ site rather thanLn³⁺(Ln³⁺=La³⁺,Lu³⁺)site.The reason for this should be ascribed to the amount change of O vacancies in the host,which was confirmed from their Raman spectra.The results might be beneficial for the system potentially used in solid state lighting as well as other optoelectronic fields.