Angular Jahn-Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn²⁺ Activators in Solids-A...

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 d⁵ system of the strongly covalent tetrahedral coordinated Mn²⁺ activator in solids. The electronic structure of the ⁴T₁ and ⁴A₁/⁴E 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 ⁶A₁ → ⁴T₁ and ⁴A₁/⁴E excitations and the ⁴T₁ → ⁶A₁ 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 ⁴T₁ states is dominated by the e-type angular distortion of the [MnL₄] moiety (L being the ligand), which accounts for the small Stokes shift of tetrahedral coordinated Mn²⁺. The results show that the ground- and excited-state electronic and geometric structures and the luminescent property of tetrahedral coordinated Mn²⁺ can be reliably predicted. The method can be further explored to interpret and discriminate the luminescent properties of materials containing a variety of different Mn²⁺ sites and complexes and even other transition metals.