Multiple-Valence and Visible to Near-Infrared Photoluminescence of Manganese in ZnGa₂O₄: A First-Principles Study

Abstract

The transition metal manganese is attractive for magnetism and luminescence engineering due to the nontrivial interplay of charge, spin, lattice, and orbital freedom degrees. Here, we report the manganese site occupancy and valence states by taking experimental synthesis conditions into consideration and the optical features of target intra-atomic Mn2+, Mn3+, and Mn4+ in the framework of density functional theory in a prototype spinel ZnGa2O4 host. The formation energy results show that Mn2+ dominates in tetrahedral ligands at the Zn2+ site and Mn3+ and Mn4+ dominate in octahedral ligands at the Ga3+ site under the corresponding different chemical potential conditions, and the distortion of the local coordination environment of Mn3+ in octahedral ligands due to the Jahn–Teller effect is studied in detail. The excited-state equilibrium geometries and energies are obtained via spin or orbital occupancy constraints, which are further complemented by the Tanabe–Sugano diagram to predict the energy spectra and to interpret the experimental results on Mn2+, Mn4+, and Mn3+. In particular, the competition of 5T2 and 1T2 excited states and the relaxation processes leading to near-infrared luminescence of rarely reported Mn3+ are analyzed. First-principles calculations complemented by the Tanabe–Sugano diagram analysis may serve as an effective and predictive tool for exploring valence states, energy structures, and luminescence of complexes containing 3d n transition-metal ions.

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

“…It has been reported that the calculated 2 E → 4 A 2 transitions overestimated the experiments by ∼0.2 eV. 28 In our work, the calculated transitions are overestimated by only ∼0.1 eV after the inclusion of nonspherical contributions. Besides, we note that since the 2 E → 4 A 2 emission of Mn 4+ is insensitive to the ligand-field strength, the experimentally observed luminescence is sharp, and the emission energies of Mn oct 4+ are close in CAGG and CGGG hosts.…”

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

“…However, it is noticed that the 4 T 1 excited states might not be attainable even based on Slater's transition-state method or the occupation matrix control methodology for sites with large distorted coordinations; the namely calculated 6 A 1 ↔ 4 T 1 transition energies would be underestimated by about 0.2 eV at the HSE06 level in these cases, and a similar underestimation has been reported previously. 64 Besides, the transition energies calculated by Slater's transition-state method at the GGA+U (U eff = 0) level are systematically underestimated by 0.6−0.7 eV compared to the experimental values, and so a systematical correction by adding a similar value is required. We attribute this to the underestimated Coulomb interaction between Mn-3d electrons (see Figure S3 in the Supporting Information).…”

“…The crystal is composed of [MgO 4 ] tetrahedra and [AlO 6 ] octahedra, and Mn 2+ prefers to substitute the tetrahedral Mg 2+ site due to the similar ionic radii and chemical properties, which has been confirmed by the formation-energy calculation, similar to the case of Mn 2+ in ZnGa 2 O 4 . 64 In the tetrahedral coordinations, as shown in Figure 1, the five 3d orbitals split into the higher 3-fold degenerate t 2 orbitals and the lower 2fold degenerate e orbitals. The ground state of Mn 2+ is the 6…”

Extended Positron‐Trapping Defects in the Eu3+‐Doped BaGa2O4 Ceramics Studied by Positron Annihilation Lifetime Method

“…[ 15–24 ] Nevertheless, doping of such ceramics not only leads to modification of their luminescent properties and changes in phase composition, but also causes structural transformation. [ 25–27 ] Such significant transformation of the inner structure in ceramics facilitates the formation of additional defect‐related free volumes. [ 28–33 ]…”

“…[15][16][17][18][19][20][21][22][23][24] Nevertheless, doping of such ceramics not only leads to modification of their luminescent properties and changes in phase composition, but also causes structural transformation. [25][26][27] Such significant transformation of the inner structure in ceramics facilitates the formation of additional defect-related free volumes. [28][29][30][31][32][33] Among the less conventional but promising methods to study the defect-related free volumes in solids of different structural types is positron annihilation lifetime (PAL) spectroscopy.…”