Narrow band deep red photoluminescence of Y₂Mg₃Ge₃O₁₂:Mn⁴⁺,Li⁺ inverse garnet for high power phosphor converted LEDs

This work concerns a novel red emitting Mn⁴⁺ doped phosphor showing an extraordinarily high thermal quenching temperature. The composition Y₂Mg₃Ge₃O₁₂:Mn⁴⁺,Li⁺ exhibits efficient red photoluminescence peaking at 658 nm, which can be assigned to the ² E_g → ⁴A_2gintraconfigurational transition of Mn⁴⁺ ([Ar]3d³ configuration) located at the octahedral site in the garnet structure. Photoluminescence properties, such as temperature dependence of the luminescence intensity and luminescence lifetime are presented. Additionally, the band structure of the undoped host material were treated with Density Functional Theory (DFT) and evaluated with UV-reflectance spectroscopy. Furthermore, the energy levels of the Mn⁴⁺ ion in the Y₂Mg₃Ge₃O₁₂ host were calculated with the exchange charge model of crystal field theory and compared to those obtained experimentally from luminescence studies.