New red-emitting phosphor Rb K_3- SiF₇:Mn⁴⁺ (x = 0, 1, 2, 3): DFT predictions and synthesis

Finding new phosphors through an efficient method is important in terms of saving time and cost related to the development of phosphor materials. The ability to identify new phosphors through preliminary simulations by calculations prior to the actual synthesis of the materials can maximize the efficiency of novel phosphor development. In this paper, we demonstrate the use of density functional theory (DFT) calculations to guide the development of a new red phosphor. We performed first-principles calculations based on DFT for pristine and Mn-doped Rb K_3- SiF₇ (x = 0, 1, 2, 3) and predicted their stability, electronic structure, and luminescence properties. On the basis of the results, we then synthesized the stable Rb₂KSiF₇:Mn⁴⁺ red conversion phosphor and investigated its luminescence, structure, and stability. As a result, we confirmed that Rb₂KSiF₇:Mn⁴⁺ emitted red light with a longer wavelength than that emitted by K₃SiF₇:Mn⁴⁺ and a wavelength similar to that of K₂SiF₆:Mn⁴⁺. These results show that DFT calculations can provide rational insights into the design of a phosphor material before it is synthesized, thereby reducing the time and cost required to develop new red conversion phosphors.