Effects of Anionic Groups on Structural and Luminescent Properties of ZnO:Sm3+ Phosphors Synthesized via Combustion Method

BO₃^3-, PO₄^3-, and SO₄^2- anionic groups were used to study their effects on the structure and luminescence of Sm³⁺-doped ZnO. ZnO, ZnO:Sm³⁺, ZnO, Zn₄B₆O₁₃:Sm³⁺, and Zn₂P₂O₇:Sm³⁺ phosphors were successfully synthesized via combustion synthesis. While BO₃^3- and PO₄^3- ions led to the formation of new crystalline phases, the sulfate precursor decomposed during synthesis, yielding ZnO with only minor surface sulfur traces. The XRD results revealed the formation of wurtzite crystal structures in the ZnO, ZnO:Sm³⁺, and ZnO-SO₄:Sm³⁺ samples, while a complete change of structure was observed after the incorporation of borate (BO₃^3-) and phosphate (PO₄^3-) ions into ZnO:Sm³⁺ to Zn₄B₆O₁₃:Sm³⁺ and Zn₂P₂O₇:Sm³⁺, respectively. The structures for borate and phosphate ions were confirmed as cubic (Zn₄B₆O₁₃) and monoclinic (Zn₂P₂O₇) crystal structures, respectively. The morphological studies of ZnO:Sm³⁺ and ZnO-SO₄:Sm³⁺ were characterized by aggregated particles with different shapes and sizes. Zn₄B₆O₁₃ and Zn₂P₂O₇ samples were characterized by having cubic and rough surfaces, respectively. The oxidation state of the Sm ions was confirmed by XPS analysis. The photoluminescence studies revealed a broad-band emission for the ZnO:Sm³⁺ and ZnO-SO₄:Sm³⁺ materials and characteristic Sm³⁺ emissions (from the ⁴G_5/2 level to lower states ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2)) for the Zn₄B₆O₁₃ and Zn₂P₂O₇ samples. Enhanced emissions were observed after the incorporation of anionic group systems. The most intense PL emission was observed from the Zn₄B₆O₁₃ phosphor material. The CIE calculations revealed that the best color purity results were from Zn₄B₆O₁₃, which lay in the orange region with 98% color purity.