北京大学严纯华团队近日揭示了锰（II）近红外辐射的来源。相关论文于2025年5月13日发表在《光：科学与应用》杂志上。

围绕Mn²⁺近红外（NIR）发射的持久谜团继续引发激烈的学术讨论。从广泛的研究工作中出现了许多假设来解释这一现象，例如Mn²⁺–Mn²⁺离子对的形成，Mn²⁺占据立方配位位点，以及推测Mn³⁺参与了Mn²⁺的氧化或缺陷。尽管有这些不同且有价值的见解，但这些假设都没有达成广泛共识。研究组观察到Mn²⁺离子的近红外发射的荧光寿命延长（~10ms），这暗示这些离子占据了石榴石晶格固有的高对称八面体位点。 

这一推断得到了X射线吸收精细结构分析和第一性原理计算的证实。与AlO₆类似，八面体位点的强晶场有助于d–d能级的分裂，从而引起发射光谱向近红外区红移，这是由于分离的Mn²⁺发生⁴T₁（4G）→⁶A₁（6S）跃迁。该发现不仅为其他Mn²⁺激活的石榴石荧光粉表现出的近红外发射提供了合理的理论基础，而且为理解Mn²⁺离子近红外发射的基本机制铺平了明确的道路。

附：英文原文

Title: Tracing the origin of near-infrared emissions emanating from manganese (II)

Author: Xiao, Yu, Yang, Xun, Zhao, Hao-Ran, Wu, Dan, Chen, Ming-Xing, Zheng, Tianxiang, Zhang, Rui, Sun, Ling-Dong, Yan, Chun-Hua

Issue&Volume: 2025-05-13

Abstract: The enduring enigma surrounding the near-infrared (NIR) emission of Mn2+ continues to ignite intense academic discussions. Numerous hypotheses have emerged from extensive research endeavors to explain this phenomenon, such as the formation of Mn2+–Mn2+ ion pairs, Mn2+ occupying cubically coordinated sites, as well as conjectures positing the involvement of Mn3+ oxidized from Mn2+ or defects. Despite these diverse and valuable insights, none of the hypotheses have yet achieved broad consensus. In this study, we have observed prolonged fluorescence lifetimes (~10ms) for the NIR emissions of Mn2+ ions, hinting at these ions occupying the high-symmetry octahedral sites inherent to the garnet lattice. This inference is supported by the corroborating results from X-ray absorption fine structure analysis and first-principles calculations. The intense crystal field of octahedral sites, similar to that of AlO6, facilitates the splitting of d–d energy levels, thereby inducing a red-shift in the emission spectrum to the NIR region due to the transition 4T1(4G)→6A1(6S) of isolated Mn2+. Our findings not only offer a plausible rationale for the NIR emission exhibited by other Mn2+-activated garnet phosphors but also pave a definitive route towards understanding the fundamental mechanisms responsible for the NIR emission of Mn2+ ions.

DOI: 10.1038/s41377-025-01816-y

Source: https://www.nature.com/articles/s41377-025-01816-y