Cyan-Light-Emitting Chalcogenometallate Phosphor, KGaS2:Eu2+, for Phosphor-Converted White Light-Emitting Diodes.

A novel KGaS2 phosphor host that emits a cyan light was discovered to fill the cyan gap in the visible spectrum of phosphor-converted white light-emitting diodes (pc-wLEDs). KGaS2, belonging to the chalcogenometallates of the type ABQ2, was synthesized via a solid-state route with compositions optimized to achieve a phosphor host that would achieve the best photoluminescence (PL) properties. The activation with Eu2+ gave rise to PL in the cyan region of the spectrum with a PL maximum at ∼498 nm, as measured under the near-UV (420 nm) and blue (450 nm) excitations. The PL properties at the near-UV excitation are found to be much better, as compared to those obtained at the blue excitation. The Rietveld analysis, using high resolution synchrotron X-ray diffraction calibrated at a wavelength of 1.522 Å and selected area electron diffraction (SAED) pattern analysis of the composition optimized with the highest PL intensity, revealed a centrosymmetric monoclinic structure in the C2/c space group. The stoichiometry of the optimized composition, as estimated using Rietveld refinement, was revealed as KGa0.921S1.882:Eu2+. The decay curve measurement, using time-resolved spectroscopy, yielded a 10% decay time of 0.41 μs, which is much smaller compared with the decay time of the commercially available β-SIALON phosphor that has a 10% decay time of 1.71 μs. The white pc-LED, fabricated with a cyan phosphor, had a higher value on the color rendering index and a lower value for color correlated temperatures, as compared with the version fabricated without a cyan phosphor, which makes this novel phosphor suitable for applications as a pc-wLED.