Luminescence and energy transfer properties of Ca8Gd2(PO4)6O2:A (A = Ce3+/Eu2+/Tb3+/Dy3+/Mn2+) phosphors

Abstract

A series of Ca₈Gd₂(PO₄)₆O₂, (CGPO):A (A = Ce³⁺, Eu²⁺, Tb³⁺, Dy³⁺, Mn²⁺, and their combination), phosphors with the oxyapatite structure have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, absolute quantum yield and lifetimes were utilized to characterize the samples. Under UV and low voltage electron beam excitation, the Ce³⁺ ion, as a sensitizer, can transfer its energy to other activators (Eu²⁺, Tb³⁺, Dy³⁺, and Mn²⁺) in the CGPO:Ce³⁺, Eu²⁺/Tb³⁺/Dy³⁺/Mn²⁺ system. The energy transfer from Ce³⁺ to Eu²⁺ and Tb³⁺ has been demonstrated to be a resonant type, via a dipole–dipole and dipole–quadrupole mechanism, respectively, and the critical distances are calculated to be 28.70 and 12.60 Å, respectively. The absolute quantum yields of the Ce³⁺ and Eu²⁺ coactivated CGPO phosphors are enhanced with respect to those of the Eu²⁺ singly activated samples via energy transfer. Under the excitation of a low voltage electron beam, the emitting colors of CGPO:Ce³⁺/Tb³⁺/Dy³⁺/Mn²⁺ samples can be adjusted from blue to green, and from blue to white to yellow-green by control of the contents of Ce³⁺, Tb³⁺, Dy³⁺, and Mn²⁺. The CL properties have been investigated in detail, and the results indicate that the as-prepared Ca₈Gd₂(PO₄)₆O₂:A (A = Ce³⁺/Eu²⁺/Tb³⁺/Dy³⁺/Mn²⁺) samples have good CL intensity and CIE coordinate stability with a wide color-tunable emission. Based on the good PL and CL properties and the varied hues of the CGPO host by adjusting the concentration of the activators (Ce³⁺/Eu²⁺/Tb³⁺/Dy³⁺/Mn²⁺), CGPO might be promising as a host material for use in solid-state lighting and display fields.