Intensive Enhancement of Near-Infrared Emission in ZnAl2O4:Fe3+ via Li-Substitution for Application in Identifying Lithium Bearing Ores

Abstract

Owing to the extensive use of lithium compounds in various strategic emerging fields, the global demand for lithium minerals has surged in recent years. However, the existing spectroscopic techniques tend to be time-consuming and inefficient. As a result, there is an urgent need for the development of efficient and rapid methods for identifying lithium ores. Here, by choosing the environment-friendly Fe³⁺ ions as activators and ZnAl₂O₄ (ZAO) spinel oxide as the host, the novel Li⁺-sensitive materials of Zn_1-xLi_xAl₂O₄:Fe³⁺ (ZLAO:Fe³⁺) near-infrared (NIR) phosphors are synthesized. The oxygen vacancy defect levels are reduced due to the occupation of interstitial sites by Li⁺, thus prohibiting detrimental electron trapping. Meanwhile, the site preference and valence state of Fe ions are altered by Li⁺ doping, resulting in more efficient utilization of excited electrons by Fe³⁺ in the octahedral sites for radiative transitions. Notably, the optimal ZLAO:Fe³⁺ (x = 0.4) phosphor presents a 53-fold higher NIR emission intensity than that of ZAO:Fe³⁺ and an outstanding thermal stability (86%@373 K, 74%@423 K). The NIR ceramic plates sensitive to additional Li⁺ are fabricated and their application in identifying lithium bearing ores is demonstrated. The proposed strategy initiates a new way to design Fe³⁺-activated NIR materials for multifunctional applications.