II-VI group phosphors stabilized by alternating Al2O3/TiO2 nanocoatings for warm white light emitting devices

We describe the synthesis and characterization of CaSe 1-x S x :Eu (0 ≤  x  ≤ 1) phosphors, uniformly coated with alternating metal oxide layers via a customized fluidized-bed chemical vapor deposition (FB-CVD) technique. Through precise sintering control, the phosphor composition is engineered for tunable red emission under 450 nm blue excitation. First-principles calculations show that Eu 2+ substitution introduces localized Eu 4f states just below the conduction band minimum, enabling efficient blue excitation and red emission, while sulfur substitution enhances lattice stability by increasing intrinsic chalcogenide migration barriers. This energy-level configuration explains efficient Eu 2+ luminescent center activation, yielding intense red emission. Moreover, Se substitution with S increases the anionic migration barrier progressively, consistent with experimental observations of CaSe 1-x S x degradation in humid environments due to Se's inherent instability. However, this moisture susceptibility is markedly reduced via uniform, conformal FB-CVD barrier coatings on individual phosphor particles. Stabilized CaSe 1-x S x phosphors serve as promising components in high-performance warm white light-emitting diodes (W-LEDs), enabling blue-to-red light conversion. As a result, fabricated W-LEDs retain >95% of initial luminance after 1000 h of operation, with negligible chromaticity coordinate shifts.