Hygrothermal degradation kinetics analysis and stability enhancement of K2GeF6:Mn4+ phosphors via plasma-assisted nanoscale silica coating

KGe 2 F 6 :Mn 4+ phosphors exhibit a narrow emission peak at 625 nm with a FWHM of only 3-5 nm, enabling their widespread use in smartphones, televisions, and automotive displays. However, as an ionic crystal consisting of K + and [GeF 6 ] 2- units with relatively weak electrostatic bonding, KGF easily develops surface water films under high-temperature and high-humidity conditions, leading to K + migration and accelerated luminescence degradation. In this study, a rapid Plasma-Assisted Film Deposition (PAFD) technique was employed to construct a nanoscale silica layer with a thickness of approximately 200 nm on KGF phosphor particles, followed by hygrothermal aging tests at 100 °C and 100 % RH. Arrhenius kinetics modelling and analysis revealed that the coating increased the apparent activation energy from 20.05 to 21.35 kJ mol −1 , suggesting improved resistance against hygrothermal degradation. First-principles calculations confirmed that water was physisorbed on all crystal facets, with the (021) surface exhibiting the highest adsorption energy (−0.80eV). Furthermore, 5 ps ab initio molecular dynamics (AIMD) simulations demonstrated that adsorbed water induced K + displacement from lattice sites, a phenomenon that intensifies with increasing temperature. The nanoscale silica coating effectively suppresses this migration. These findings demonstrate that the rapid plasma-assisted coating strategy significantly enhances KGF's hygrothermal stability and ensures reliable performance in demanding harsh environments.