Highly efficient and thermally stable cyan-emitting ZnS/ZnO phosphors for full-visible-spectrum LED lighting

Near-ultraviolet (NUV)-pumped white light-emitting-diodes (WLEDs) often suffer from poor color rendering in the 480-520 nm range, highlighting the need for an efficient cyan phosphor with strong absorption at 370-420 nm. This study presents the successful synthesis of cyan-emitting ZnS/ZnO phosphors using a high-energy planetary ball milling method followed by post-annealing. The fabricated phosphors, with particle sizes ranging from 1 to 3 μm, exhibit strong cyan emission with CIE chromaticity coordinates of (0.2302, 0.3759) and excellent thermal stability with an activation energy of 0.26 eV. A prototype near-ultraviolet (NUV)-pumped cyan LED was developed, achieving chromatic coordinates of (0.2769, 0.4380) and a quantum efficiency of 77% by coating an NUV chip at 370 nm with the synthesized phosphor. These results demonstrate the potential of ZnS/ZnO-based materials as efficient, non-toxic alternatives to rare-earth phosphors, paving the way for advancements in full-spectrum white LEDs for solid-state lighting.