Realization of color tuning via solid-solution and energy transfer in Ca3−xSrx(PO4)2:Eu2+,Mn2+ phosphors
Abstract
Three series of phosphors, namely, Ca3−xSrx(PO4)2:0.015Eu2+, Ca2.5Sr0.5(PO4)2:yEu2+ and Ca2.5Sr0.5(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 Ca3−xSrx(PO4)2:0.015Eu2+ (0 ≤ x ≤ 2). The crystallographic sites of Eu2+ in the Ca2.5Sr0.5(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 Ca2.5Sr0.5(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 Ca2.5Sr0.5(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.