Angular Jahn-Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn 2+ Activators in Solids-A First-Principles Study.

First-principles calculations based on density functional theory have been performed to investigate the electronic structure, excited-state Jahn-Teller distortion, and photoluminescence of the multielectron d 5 system of the strongly covalent tetrahedral coordinated Mn 2+ activator in solids. The electronic structure of the 4 T 1 and 4 A 1 / 4 E excited states is analyzed, and Slater's transition-state method and occupation matrix control methodology are applied to deal with the spin contamination in the lower-spin excited states, which is due to the mixing of the ground state of the same spin projection number. In a series of covalent tetrahedral coordinations, the 6 A 1 → 4 T 1 and 4 A 1 / 4 E excitations and the 4 T 1 → 6 A 1 emission energies are obtained and compared to the reported experimental results. The nephelauxetic effect follows O 2- < S 2- ≈ Se 2- < N 3- , and the larger nephelauxetic effect and crystal field strength lead to the red-shifted emission of nitride phosphors. The Jahn-Teller distortion of the 4 T 1 states is dominated by the e -type angular distortion of the [Mn L 4 ] moiety ( L being the ligand), which accounts for the small Stokes shift of tetrahedral coordinated Mn 2+ . The results show that the ground- and excited-state electronic and geometric structures and the luminescent property of tetrahedral coordinated Mn 2+ can be reliably predicted. The method can be further explored to interpret and discriminate the luminescent properties of materials containing a variety of different Mn 2+ sites and complexes and even other transition metals.