Lithiation-Driven Phase Engineering Unlocking Broadband NIR Emission in Cr-Doped Zinc Tantalate

Abstract

Structural phase evolution is among the most powerful tools for tuning material properties, enabling advancements in catalysis, dielectrics, optoelectronics, and photoluminescence. Such an evolution can significantly enhance the near-infrared (NIR) emission properties of Cr³⁺-doped phosphors. Herein, we present, to the best of our knowledge, the first observation of lithiation-induced continuous structural phase evolution in ZnTa₂O₆ phosphors, driven by Li⁺ incorporation. This evolution proceeds systematically from orthorhombic ZnTa₂O₆ (Pbcn) to tetragonal ZnTa₂O₆ (P4₂/mnm) and ultimately to trigonal (Li_0.5Zn_0.5)TaO₃ (R3c) as the Li⁺ content increases. When doped with Cr³⁺, the NIR emission peak exhibits a progressive blue shift, moving from 949 to 885 nm and eventually to 862 nm, in tandem with the phase evolution. This phase evolution also yields significant enhancements in photoluminescent intensity, internal quantum yield (IQY), and photoluminescence thermal stability. Our findings establish a new paradigm for designing highly efficient ultra-broadband NIR phosphors and offer a foundation for developing tantalate-based materials with versatile functionalities, including improved dielectric properties.