We found that substitution of not only a larger ion like Ba 2+ [J. Am. Ceram. Soc., 93, 138 (2010)] but also a smaller one like Mg 2+ (this paper) replacing no >14.9% Ca 2+ ions could enhance integrated down-shifting (DS) emission intensity of red phosphor Ca 3(VO 4) 2:0.12Eu 3+, indicating that both lattice expansion and contraction can decrease the site symmetry of Eu 3+ in Ca 3(VO 4) 2:0.12Eu 3+ phosphor. This finding is anticipated to improve the Eu 3+ emission intensity of other Eu 3+-doped phosphors. To further investigate Eu 3+ up-conversion (UC) behaviors, Yb 3+ ion was used as a sensitizer. Interestingly, 5D 1 → 7F 3,4,6 transitions of Eu 3+, which were barely detectable under DS excitation, exhibited strong intensity under UC excitation. A "recycling" process, arising from the 5D 1 → 7F 3 transition of Eu 3+ and cross-relaxation Eu 3+ ( 7F 3) + Eu 3+ ( 5D 0) → Eu 3+ ( 7F 0) + Eu 3+ ( 5D 1), is presumably the leading mechanism of such inconsistency.
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