Structure and photoluminescence properties of Na₂Y ₂B₂O₇:Ce³⁺,Tb³⁺ phosphors for solid-state lighting application

Novel phosphors of Na₂Y₂B₂O ₇:Ce³⁺ and Na₂Y₂B₂O ₇:Ce³⁺,Tb³⁺ were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce³⁺ emission properties and the crystal structure of Na₂Y₂B₂O₇ is built and the result shows that Ce³⁺ ions occupy two non-equivalent Y³⁺ sites in the host. The codoping of Tb³⁺ in Na₂Y ₂B₂O₇:Ce³⁺ can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce³⁺→Tb³⁺. The energy transfer processes of Ce³⁺-Ce³⁺ and Ce ³⁺-Tb³⁺ are analysed and determined to be electric dipole-dipole and dipole-quadrupole, respectively. The broad PLE spectra of Na₂Y₂B₂O₇:Ce³⁺ and Na₂Y₂B₂O₇:Ce³⁺,Tb ³⁺ are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs.