Achieving Deep Red Emission in Mn-Activated KMgGeO Phosphor with a Tetrahedral Network for Light-Emitting Diodes.

Designing a thermally robust Mn-based red-emitting phosphor is essential for warm phosphor-converted light-emitting diodes (pc-LEDs) with improved CRI and indoor plant cultivation applications. However, the major constraint is selecting a host with octahedral crystallographic sites and poor thermal stability. Herein, we report the stabilization of Mn ions in tetrahedral coordination in a KMgGeO matrix. The combined experimental and theoretical results confirmed the location of Mn in tetrahedral coordination, preferably occupied at GeO lattice sites of KMgGeO. The Mn-doped KMgGeO phosphors emit deep red emission (662 nm), and the temperature-dependent photoluminescence study revealed good thermal stability of KMgGeO:Mn phosphor, retaining 70% of the initial emission intensity at 423 K. The defect formation energies calculated for various defects using density functional theory, thermoluminescence measurement, and positron annihilation lifetime spectroscopy confirmed the presence of cation vacancies (V, V) and V with wide-ranging trap depths (∼0.8 to 1 eV). The thermal quenching mechanism and defect-assisted thermal stability of Mn emission are discussed in detail. Finally, a red pc-LED device was fabricated using a KMgGeO:Mn phosphor and a UV-LED chip to demonstrate its potential for indoor plant growth. This work explored the stabilization of Mn in the tetrahedral crystal field, which will open new directions for matrix selection of multifunctional red-emitting phosphors.