Influence of Anion/Cation Substitution (Sr²⁺ → Ba²⁺, Al³⁺ → Si⁴⁺, N^3– → O^2–) on Phase Transformation and Luminescence Properties of Ba₃Si₆O₁₅:Eu²⁺ Phosphors

Abstract

A series of promising cyan, green, and yellow emission (Ba, Sr)₃(Si, Al)₆(O, N)₁₅:Eu²⁺ phosphors were synthesized by a Pechini-type sol–gel ammonolysis method. Variations in luminescence properties and crystal structure caused by the modification of phosphor composition were studied in detail. The prefired temperatures of the precursors play a key role in the process of forming the final products. Under UV light excitation, the as-prepared Ba₃Si₆O₁₅:Eu²⁺ phosphor presents a strong cyan emission located at 498 nm. Moreover, the as-prepared oxynitride phosphors, Eu²⁺-activated (Ba_1–<i>y</i>Sr_<i>y</i>)₃Si_6–<i>x</i>Al_<i>x</i>O_15−μN_δ (<i>x</i> = 0–1.2, <i>y</i> = 0–0.6), display a broader excitation band covering the entire visible region. Under blue light excitation, Ba₃Si_6–<i>x</i>Al_<i>x</i>O_15−μN_δ:Eu²⁺ phosphors show a intense and narrow green emission at 520 nm, and the luminescent intensity can be enhanced by increasing Al content within a certain range. However, (Ba_1–<i>y</i>Sr_<i>y</i>)₃Si₆O_15−μN_δ:Eu²⁺phosphors exhibit green (520 nm) to yellow (554 nm) emission with increasing Sr content. Unexpectedly, Eu²⁺ doped Ba₃Si₆O₉N₄-type Ba₃Si₆O_15−μN_δ–1300 °C phosphor exhibits a bluish green emission and strong thermal quenching behavior. The (Ba_1–<i>y</i>Sr_<i>y</i>)₃Si_6–<i>x</i>Al_<i>x</i>O_15−μN_δ:Eu²⁺ phosphors exhibit a small thermal quenching, and the quantum yields measured under 460 nm excitation could reach up to 89% for green Ba₃Si_6–<i>x</i>Al_<i>x</i>O_15−μN_δ:Eu²⁺ phosphor and 71% for yellow (Ba_1–<i>y</i>Sr_<i>y</i>)₃Si_6<i>x</i>O_15−μN_δ:Eu²⁺ phosphor. White LEDs with tunable color temperature and higher color rendering index were fabricated by combining the prepared cyan Ba₃Si₆O₁₅:Eu²⁺/green Ba_2.91Eu_0.09Si_6–<i>x</i>Al_<i>x</i>O_15−μN_δ (<i>x</i> = 0.06)/yellow (Ba_{0.97–<i>y</i>}Sr_<i>y</i>)₃Eu_0.09Si₆O_15−μN_δ (<i>y</i> = 0.4) phosphor and a red phosphor with a UV or blue LED chip, indicating that they are promising phosphors for white LEDs