Unveiling the Local Structure and Luminescence Mechanism of Er3+-Doped LiYF4: A Promising Near-Infrared Laser Crystal

Visible and near-infrared laser radiation based on Er3+-doped LiYF4 (YLF:Er3+) crystals has attracted considerable attention because of its important use in biosensing, luminescence thermometry, and anticounterfeiting applications. However, the key issues such as the microstructure and luminescencet mechanism have not been well established yet, impeding the in-depth understanding of optical behavior. Herein, a detailed structural analysis was investigated by the crystal structure prediction method and first-principles calculations. A new tetragonal structure for Er3+-doped LiYF4 is uncovered, which is energetically and dynamically stable. Meanwhile, the complete Stark levels of Er3+ ions in a YLF crystal are further revealed based on our newly developed well-established parametrization matrix diagonalization (WEPMD) method. The main spectroscopic parameters of Er3+-doped LiYF4, including fluorescence branching ratios, spontaneous transition rates, line strengths, and radiative lifetimes, were studied systematically. Noticeably, two prominent emission bands peaked at 809 and 990 nm are identified, which originated from the 4I9/2 → 4I15/2 and 4I11/2 → 4I15/2 transitions of Er3+ ions, respectively. The above results imply that the predicted laser transition channels of Er3+-doped LiYF4 have a potential application in lasing materials. Furthermore, our study provides a new strategy for the design of lasing materials.