Crystallization and architecture engineering of ZnWO4 for enhanced photoluminescence

Abstract

Oxalic acid (H₂C₂O₄) and (NH₄)₂SO₄ were originally examined as crystallization and architecture directing reagents for the hydrothermal synthesis of ZnWO₄, with the pivotal roles of the C₂O₄²⁻/Zn²⁺ (R) and SO₄²⁻/Zn²⁺ (R′) molar ratios and hydrothermal temperature/duration investigated in detail. It was clearly demonstrated that C₂O₄²⁻ remarkably altered the reaction pathway and suppressed the intrinsic 1D growth of ZnWO₄, eventually leading to 2D crystallites with exposed ab planes. (NH₄)₂SO₄ further promoted 2D growth and self-assembly of the ZnWO₄ crystallites, leading to flower-like architectures of up to ∼2.5 μm sized large microplates. Photoluminescence properties were thoroughly analyzed and discussed for the representative ZnWO₄ and (Zn_0.98Eu_0.02)WO₄ products after 700 °C calcination to show the importance of crystallite/architecture engineering.