Red and Deep Red Emissions from Cubic K₂SiF₆:Mn⁴⁺and Hexagonal K₂MnF₆Synthesized in HF/KMnO₄/KHF₂/Si Solutions

Cubic K 2 SiF 6 :Mn 4+ and hexagonal ( h -) K 2 MnF 6 red phosphors are synthesized in HF/KMnO 4 /KHF 2 /Si solutions under KMnO 4 -rich and KHF 2 -rich conditions, respectively. K 2 SiF 6 :Mn 4+ exhibits efficient red photoluminescence (PL) emission at ∼630 nm. h -K 2 MnF 6 also exhibits red emission at ∼630 nm and deep red emission at ∼680 nm; however, the deep red emission undergoes considerable thermal quenching above 100 K. These two emission bands observed in h -K 2 MnF 6 have the same PL excitation bands as those in K 2 SiF 6 :Mn 4+ . The red emissions can be assigned to the 2 E g → 4 A 2g transition of the 3 d 3 electrons in the octahedra of h -K 2 MnF 6 and K 2 SiF 6 . The deep red emission in h -K 2 MnF 6 is considered to arise from a strongly distorted Mn 4+ center in its hexagonal lattice. PL properties, such as the temperature dependence of the PL intensity and luminescence lifetime, of h -K 2 MnF 6 are presented in details in comparison with those of K 2 SiF 6 :Mn 4+ . The addition of KHF 2 is also found to be not so efficient to control the Mn doping level in K 2 SiF 6 :Mn 4+ .