Color tuning and energy transfer in Eu2+/Mn2+-doped Ba3Y(PO4)3 eulytite-type orthophosphate phosphors

Abstract

Eulytite-type orthophosphate phosphors Ba₃Y(PO₄)₃:Eu²⁺, Mn²⁺ and Ba₃Ln(PO₄)₃:Eu²⁺ (Ln = Lu, Y and Gd) were synthesized by high-temperature solid state reactions under reductive atmospheres. Their photoluminescence showed a surprising red-shift in the emission spectrum with the increase in the ionic radius of Ln in the Ba₃Ln(PO₄)₃:Eu²⁺ (Ln = Lu, Y and Gd) phosphors system, which arises from the splitting of the 5d energy level. The phase formation, luminescence properties, and energy-transfer mechanism from the Eu²⁺ to the Mn²⁺ ions, and the CIE coordinates in the Ba₃Y(PO₄)₃:Eu²⁺, Mn²⁺ phosphors were investigated. From powder X-ray diffraction (XRD) analysis, the formation of the single-phased Ba₃Y(PO₄)₃ in a cubic crystal system with the space group I3d (no. 220) was confirmed. With the doping of Mn²⁺, the spectral overlap between the emission spectrum of Eu²⁺ and the excitation spectrum of Mn²⁺ allows resonance-type energy transfer to occur from Eu²⁺ to Mn²⁺ with the mechanism carefully studied by luminescence spectra, energy transfer efficiency and decay times. By increasing the Mn²⁺ doping concentration in the Ba₃Y(PO₄)₃:Eu²⁺, Mn²⁺ phosphors, the emission colors can be tuned from yellowish-green through yellow and ultimately to orange. Such color tuning emissions originate from the change in intensity between the 4f–5d transitions of the Eu²⁺ ions and the ⁴T₁–⁶A₁ transitions of the Mn²⁺ ions through the energy transfer from the Eu²⁺ to the Mn²⁺ ions. In particular, compared with the commercial YAG:Ce phosphor, our developed phosphor contains a larger amount of red-emitting component; thus, it possesses favorable properties for application in warm white LEDs.