(Luminescence and Display Materials Division Centennial Outstanding Achievement Award Address) Investigation of Luminescent Materials based on First-principles Calculations of Multiplet States

The transitions between multiplet states of rare-earth (RE) and transition-metal (TM) ions in crystals are utilized in variety of luminescent materials. Therefore, for the theoretical design of novel luminescent materials, a deep understanding of multiplet states and a nonempirical prediction of multiplet spectra are indispensable. For these purposes, a configuration interaction calculation program based on the discrete-variational Xa (DV-Xa) molecular orbital method [1] was developed, which is known as the discrete-variational multi-electron (DVME) program [2]. There is also a relativistic version of the DVME program [3] based on the relativistic DV-Xa method [4], which is especially useful for the analysis of RE-doped luminescent materials [5] since both the relativistic effects and the many-electron effects can be considered simultaneously without any empirical parameters. The DVME calculations have been applied to analyze various luminescent materials such as ruby [2], Mn4+-doped fluorides [6] and RE-doped LiYF4 [5]. Various types of multiplet spectra originating from d-d, f-f, f-d, and charge transfer (CT) [7, 8] transitions have been reproduced without any empirical parameters and the origins of the spectral peaks have been elucidated based on the configuration analysis of the explicitly obtained many-electron wave functions. In addition, relationships between the multiplet energy and the local structure of TM ions in crystals have been investigated in detail by creating various energy-structure maps based on systematic DVME calculations. The systematic data obtained by first-principles calculations can be also used as the training data for machine learning to create a simple predictive model. In this lecture, some representative results of the investigation of luminescent materials based on first-principles calculations of multiplet states using the DVME program will be presented. [1] H. Adachi, M. Tsukada, and C. Satoko, J. Phys. Soc. Jpn., 45, 875 (1978). [2] K. Ogasawara T. Ishii, I. Tanaka, and H. Adachi, Phys. Rev. B, 61 143 (2000). [3] K. Ogasawara, T. Iwata, Y. Koyama, and T. Ishii, I. Tanaka, and H. Adachi, Phys. Rev. B, 64, 115413 (2001). [4] A. Rosén, D.E. Ellis, H. Adachi, and F.W. Averill, J. Chem. Phys., 65, 3629 (1976). [5] K. Ogasawara, S. Watanabe, H. Toyoshima, M.G. Brik, Handbook on Physics and Chemistry of Rare Earths, 37, 1 (2007). [6] M. Novita, T. Honma, B. Hong, A. Ohishi, K. Ogasawara, J. Lumin. 169, 596 (2016). [7] S. Takemura, K. Ogasawara, Opt. Mater.: X, 1, 100005 (2019). [8] S. Takemura, K. Ogasawara, J. Lumin. 214, 116542 (2019).