Figure 1. Schematic synthetic process of the KSF:Mn⁴⁺ phosphor.

Figure 2. (a) XRD patterns of KSF:Mn⁴⁺ phosphor before and after washing with acetic acid and standard patterns of cubic KSF (c-KSF),hexagonal KSF (h-KSF), and KCl. (b) SEM morphology image of KSF:Mn⁴⁺. (c) EDS elemental mappings of KSF:Mn4+ after washing with acetic acid.

Figure 3. (a) PL and PLE spectra of KSF:6%Mn4+. (b) Histogram of the luminescence intensity vs Mn⁴⁺ ion concentration. The orange column presents the luminescence intensity of the KSF:6%Mn⁴⁺&KCl sample. (c) UV−vis−NIR diffuse reflectance spectra of KSF:x%Mn⁴⁺ samples. (d) Luminescence decay curves of KSF:x%Mn⁴⁺ samples. The inset shows the lifetimes dependent on the Mn4+ ion concentration.

Figure 4. (a) SEM morphology and EDS elemental mappings of KSF:Mn⁴⁺@CaF₂. (b) PL spectra and (c) luminescence IQE and EQE values of KSF:Mn⁴⁺&KCl, KSF:Mn⁴⁺, and KSF:Mn⁴⁺@CaF₂ samples.

Figure 5. (a) Normalized luminescence intensity of KSF:Mn⁴⁺, KSF:Mn⁴⁺@CaF₂, and KSF:Mn⁴⁺ (TEOS) phosphors before and after processing with 85 °C temperature and 85% humidity for different times. (b) Photographs under indoor light with different processing times. (c) Temperature-dependent (80−500 K) luminescence color mapping of KSF:Mn⁴⁺@CaF₂ phosphor. (d) CIE 1931 color coordinates of KSF:Mn⁴⁺@CaF₂phosphor at different temperatures.