Exploration of the structural and optical properties of a red-emitting phosphor K₂TiF₆:Mn⁴⁺

The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode (WLED) devices. Transition metal Mn-doped compounds are fascinating luminescent materials. Herein, we performed a systematic theoretical study of the microstructure and optical properties of K₂TiF₆:Mn⁴⁺ using the CALYPSO structure search method in combination with first-principles calculations. We uncovered a novel structure of K₂TiF₆:Mn⁴⁺ with space group P-3m1 symmetry, where the impurity Mn⁴⁺ ions are accurately located at the center of the MnF₆ octahedra. Based on our developed complete energy matrix diagonalization (CEMD) method, we calculated transition lines for ²E_g→⁴A₂, ⁴A₂→⁴T₂, and ⁴A₂→⁴T₂ at 642 nm, 471 nm, and 352 nm, respectively, which are in good agreement with the available experimental data. More remarkably, we also found another transition (⁴A₂→²T₂) that lies at 380 nm, which should be a promising candidate for laser action.