Realization of color hue tuning via efficient Tb3+–Mn2+ energy transfer in Sr3Tb(PO4)3:Mn2+, a potential near-UV excited phosphor for white LEDs

Abstract

A n-UV convertible phosphor Sr₃Tb(PO₄)₃:Mn²⁺ with tunable-emitting color has been synthesized by solid state reaction. The GSAS refinement shows that the obtained powder crystallizes as a cubic unit cell with space group I3d, and Mn²⁺ ions occupy the Sr²⁺ crystallographic sites. Under ⁷F₆ → ⁵D₃ of Tb³⁺ excitation at 381 nm, Sr₃Tb(PO₄)₃:Mn²⁺ not only exhibits ⁵D₄ → ⁷F_6–3 of Tb³⁺ green emission lines but also ⁴T₁ → ⁶A₁ of the Mn²⁺ orange emission band. In addition, the intensity ratio of the orange/green emission bands can be enhanced through the increase of Mn²⁺ content. The intense orange emission band of the Mn²⁺ ions is attributed to the efficient energy transfer from the Tb³⁺ to Mn²⁺ ions, which has been justified through the luminescence spectra and fluorescence decay dynamics. The energy transfer mechanism was demonstrated to be the electric dipole–dipole interaction based on the Inokuti–Hirayama theoretical model, and the energy transfer efficiency was calculated. Optimal-composition samples show high external quantum efficiency, up to 59.3%, indicating the potential of the powder as a n-UV convertible phosphor for white LEDs.