Potassium‐Impurity‐Modulated Self‐Trapped Excitons and Energy Transfer in Phase‐Separated, Mn 4+ ‐Doped Li 2 HfF 6
Menuka Adhikari, Thomas Murray, Cameron J. Lewis, Jett Wu, Hari Adhikari, Cheng Li, Jianguo Wen, Hui Wu, Zhiping LuoABSTRACT
Self‐trapped excitons (STEs) play an important role in the luminescence of halide materials, yet their formation and manipulation in complex fluorides remain largely underexplored. Here, Mn 4+ ‐doped Li 2 HfF 6 phosphors were synthesized by room‐temperature coprecipitation to investigate impurity‐modulated STEs and their role in Mn 4+ sensitization. High‐resolution neutron powder diffraction reveals impurity‐associated phase separation into two closely related Li 2 HfF 6 lattices. Photoluminescence and cathodoluminescence measurements resolve two broad host‐emission components: STE1, assigned to intrinsic Li 2 HfF 6 , and redshifted STE2, associated with a K‐containing lattice. Under high‐energy cathodoluminescence excitation, enhanced Mn 4+ red emission correlates with STE2 emission but not with STE1 emission, supporting a selective STE2 → Mn 4+ energy‐transfer pathway. Density functional theory ΔSCF (self‐consistent field) calculations yield distinct relaxed STE1 and STE2 configurations, confirming the K‐induced redshift of the STE emission. These results identify K‐associated STE2 as a key sensitizing state for Mn 4+ luminescence, establishing impurity modulation as an effective strategy for tuning excitonic emission and host‐to‐activator energy transfer in complex fluoride phosphors.