Angular Jahn–Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn²⁺ Activators in Solids–A First-Principles Study

Abstract

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 [MnL 4 ] moiety (L being the ligand), which accounts for the small Stokes shift of tetrahedral coordinated Mn 2+ . The results show that the groundand 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.

Mechanistic insights for regulating the site occupancy, valence states and optical transitions of Mn ions in yttrium–aluminum garnets via codoping

“…The influences of different U eff , k-point mesh and HSE06 method on the optimized structures and transition energies have been discussed previously. 19,38 As a compromise between accuracy and computational resources of hybrid functional HSE06 calculations, 400 eV was applied for the kinetic energy cutoff and only one G-point was applied to sample the Brillouin zone for the supercell. The conjugate gradient method was used for the geometric optimizations until the Hellmann-Feynman forces on atoms were less than 0.01 eV Å À1 .…”

“…The excited states and optical transitions of Mn 2+ , Mn 3+ and Mn 4+ ions in various hosts are separately investigated in our previous works. 19,37,38 In the DFT framework, the multiplet states are rationally approximated with the combination of single determinants. A spin multiplicity control method supplemented by a constrained occupancy approach is adopted for the excitedstate calculations.…”

Unraveling Broadband Near-Infrared Luminescence in Cr3+-Doped Ca3Y2Ge3O12 Garnets: Insights from First-Principles Analysis

“…Notably, such a coordination environment results in two distinct Ca-O distances (2.469 and 2.560 Å). Slater's transition-state method [30,31] was employed to estimate the 4 A 2 -4 T 2 excitation and emission energies, respectively, at the equilibrium geometric structures of the ground 4 A 2 and excited 4 T 2 states. This process involves examining the disparities in energy between the lowest e g and highest t 2g KS orbitals in the density of states (DOS) diagrams obtained from such calculations based on the single-electron configuration t 2g 2.5 e g 0.5 , as depicted in Figure 1.…”

Elucidating the Multisite and Multivalence Nature of Mn Ions in Solids and Predicting Their Optical Transition Properties: A Case Study on a Series of Garnet Hosts

“…For dodecahedral Mn 2+ , Slater's transition method is applied to address the spin contamination problem in 4 T 1 excited states similar to our previous work on tetrahedral Mn 2+ . 29 To check the excited state, the partial charge density distribution is analyzed and the overlap of the wave functions of the occupied orbital of the minority spin and the unoccupied orbital of the majority spin is calculated, which show that the two orbitals are orthogonal, and the spin contamination is eliminated (see Note S2 of the Supporting Information). Then, the 6 A 1 → 4 T 1 excitation energy, 4 T 1 → 6 A 1 emission energy, and Stokes shift are calculated, as shown in Table 1.…”

“…Here, garnet hosts, including Ca 3 Al 2 Ge 3 O 12 (CAG G ), Ca 3 Ga 2 Ge 3 O 12 (CGG G ), and Ca 3 Sc 2 Si 3 O 12 (CSS G ), are chosen as a series of prototype systems. First-principles calculations based on density functional theory in the periodic supercell formalism have been successfully applied in the study of the optical transitions of Mn activator centers , in solids, including Mn 2+ , Mn 3+ , and Mn 4+ . Here, we propose a theoretical scheme and demonstrate its capability of revealing the preferable manganese site occupancies and valence states with chemical conditions and predicting their optical transition properties in a garnet series.…”