Realization of color tuning via solid-solution and energy transfer in Ca3−xSrx(PO4)2:Eu2+,Mn2+ phosphors

Abstract

Three series of phosphors, namely, Ca_3−xSr_x(PO₄)₂:0.015Eu²⁺, Ca_2.5Sr_0.5(PO₄)₂:yEu²⁺ and Ca_2.5Sr_0.5(PO₄)₂:0.015Eu²⁺, zMn²⁺, are synthesized via a high-temperature solid-state reaction. The partial substitution of Ca²⁺ by Sr²⁺ formed a solid-solution of Ca_3−xSr_x(PO₄)₂:0.015Eu²⁺ (0 ≤ x ≤ 2). The crystallographic sites of Eu²⁺ in the Ca_2.5Sr_0.5(PO₄)₂ host have been identified by photoluminescence spectral analysis. The relationship among four different Eu²⁺ luminescence centers originating from four different Ca/Sr crystallographic sites has been determined and verified. The color of the Eu²⁺ emission can be tuned from blue to greenish yellow by modifying the composition of the host lattice of a solid solution with similar whitlockite structure. In addition, on tuning the Eu²⁺/Mn²⁺ ratio via the energy transfer varied the emission color of Ca_2.5Sr_0.5(PO₄)₂:0.015Eu²⁺,zMn²⁺ from blue-green (0.24, 0.35) to white-light (0.33, 0.33) and eventually to red (0.46, 0.31). Our results suggest that the single-phased Ca_2.5Sr_0.5(PO₄)₂:0.015Eu²⁺,0.05Mn²⁺ phosphor may have a potential application as a near-UV convertible white-light emission phosphor for white LEDs. More importantly, a facile route based on the Grassman's law of color mixing has been provided to realize a white light emission to meet the needs of different illumination applications.