稀土发光材料理论计算方法研究现状

Current Status of Theoretical Approaches to Rare Earth Luminescent Materials

稀土发光材料在激光、照明、显示、辐射探测等众多领域起着至关重要的作用,建立相应的微观理论对于稀土发光材料的进一步发展和应用有着重要的科学意义。然而,由于4f电子复杂的多组态特征和很强的相对论效应,使得对稀土发光性质的理论研究到目前为止主要集中在经验或半经验模型的层面上,不依赖于任何经验信息的第一性原理方法仍然面临很大的挑战。尽管如此,稀土发光材料的第一性原理计算近年来也取得了重要的进展。在波函数方法方面,发展了相对论多电子离散变分和基于嵌入簇模型的多组态从头算方法等适合于镧系掺杂材料的方法;密度泛函理论方法也被越来越多地应用于这类材料的电子结构计算,并发展出了约束占据数、限制性开壳层Kohn-Sham等针对特殊类型激发态的近似计算方法。本文回顾了传统晶体场理论和Dorenbos经验模型对稀土发光微观机制的描述,梳理总结了针对稀土发光性质的第一性原理计算方法的最新发展和应用,并对未来可能的发展方向提出展望。

Rare earth luminescent materials play an important role in various advanced technologies including laser, lighting, display and radiation detection. Establishment of the corresponding microscopic theories is of great scientific significance for further developments and applications of these materials. However, due to the complex multi-configurational characters and strong relativistic effects of 4 f electrons in lanthanide elements, theoretical understanding of luminescent properties of rare earth materials has been mainly focused on empirical and semi-empirical models so far, and first principles approaches, which do not rely on any empirical information, are still confronted with great challenges for these materials. Nevertheless, significant progress has been made in first principles-based theoretical study of rare earth luminescent materials in recent years. In the framework of wave-function theory, the relativistic discrete variational multi-electron method and the multi-configurational ab initio embedded-cluster method have been developed for lanthanide doped materials. In the meanwhile, there is growing interest in the development and application of density-functional theory(DFT) based methods to the investigation of electronic structures of such materials. The constrained occupancy approximation and restricted open shell Kohn-Sham approach are two promising methods that can efficiently describe luminescent properties of materials dominated with some specific excitations. In this review, after a short overview on the description of rare earth luminescence based on conventional crystal field theory and the Dorenbos empirical model, we summarized the latest developments and application of first principles approaches to luminescent properties of rare earth, and remarked on the limitation of the current methods and the possible new developments in the future.