Broadband-excited and green-red tunable emission in Eu2+-sensitized Ca8MnTb(PO4)7 phosphors induced by structural-confined cascade energy transfer

Abstract

Novel green-red color-tunable Ca₈(Mg,Mn)Tb(PO₄)₇:Eu²⁺ phosphors have been synthesized via the traditional solid-state method. Since Tb³⁺/Mn²⁺ ions are the parent ions in the lattice, the structural confinement occurs when the sensitizer Eu²⁺ is introduced into the Ca₈(Mg,Mn)Tb(PO₄)₇:Eu²⁺ structure. The distance from Eu²⁺ to Tb³⁺/Mn²⁺ is confined in the 5 Å range, which induces a highly efficient energy transfer process. At Eu²⁺ 350 nm excitation, Ca₈MgTb(PO₄)₇:Eu²⁺ shows dominant Tb³⁺ green emission with almost-vanished Eu²⁺ emission. Red emission is clearly observed as Mn²⁺ ions doping into Ca₈MgTb(PO₄)₇:Eu²⁺, and color-tuning from green to red is realized by varying the Mn²⁺ contents. Eu²⁺–Tb³⁺–Mn²⁺ cascade energy transfer process is in effect due to short Eu²⁺–Tb³⁺/Mn²⁺ and Tb³⁺–Mn²⁺ distances, which is verified by PL and decay variations. Meanwhile, the Ca₈(Mg,Mn)Tb(PO₄)₇:Eu²⁺ phosphor indicates good thermal stability and maintained the 45% emission level at 150 °C, which demonstrates their potential applications in white light LEDs.