New insight into the structure evolution and site preferential occupancy of Na2Ba6(Si2O7)(SiO4)2:Eu2+ phosphor by cation substitution effect

Publication date: 25 March 2017
Source:Journal of Alloys and Compounds, Volume 698
Author(s): Yingli Zhu, Yujun Liang, Shiqi Liu, Xingya Wu, Rui Xu, Kai Li
A series of single-phased Na2Ba5.99-x(Si2O7)(SiO4)2:0.01Eu²⁺, xMg²⁺ and Na2Ba5.99-y(Si2O7)(SiO4)2:0.01Eu²⁺, yZn²⁺ phosphors have been successfully prepared via the solid-state reaction. Structural refinement, luminescence property, color tuning and thermally stability were systematically investigated. The as-prepared Na2Ba6(Si2O7)(SiO4)2:0.01Eu²⁺ phosphor showed broad excitation bands from 250 nm to 450 nm and presented wide emission bands under 365 nm excitation, which could be decomposed by Gaussian fitting into three peaks corresponding to different Eu luminous centers named Eu1, Eu2 and Eu3. By substituting Mg²⁺ or Zn²⁺ for Ba²⁺, the relative intensities of Eu1, Eu2 and Eu3 emission bands changed gradually. Combined with the variation tendencies of BaO bond lengths by Rietveld refinement, the possible mechanism of the luminescence transformation of Eu²⁺ ion was the preferential occupancy of Eu²⁺ at different crystallographic sites. In addition, the introduction of Mg²⁺ ion expressed more obvious improvement on the thermal quenching behaviors of Eu²⁺ than Zn²⁺ ion in this matrix. The emission intensities of Eu2 and Eu3 could be enhanced from 63.2% to 82.7% and 35.1%–46.8% at 373 K compared to the initial intensity when Mg²⁺ concentration was 0.10. Generally, this work sheds some new lights on the design and structure explanation of preferential occupancy at different crystallographic sites in phosphors.

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