Synthesis, crystal structure and photoluminescence properties of Mn4+ activated K2WO2F4·H2O

Oxyfluorides activated with Mn 4+ have great potential in phosphors converted LED. Phosphors with intensive zero phonon line (ZPL) emission are expected to improve the performance of the light sources. Microcrystalline powders of oxyfluoride K 2 WO 2 F 4 ·H 2 O activated with Mn 4+ were synthesized by using a coprecipitation method. The structural parameters and atomic coordinations of K 2 WO 2 F 4 ·H 2 O were determined by both refinement and calculation. K 2 WO 2 F 4 ·H 2 O crystallizes in the monoclinic crystal system with C2/m group space. The unit cell could be considered as a stack of KWO 2 F 4 slices with another K + ion and H 2 O molecule in the interstitial. The morphology and photoluminescence properties of K 2 WO 2 F 4 ·H 2 O: Mn 4+ were studied as a function of Mn 4+ concentration. It is revealed that the microcrystalline shows highly orientational preferred growth. Mn 4+ shows bright red emission upon the excitation of blue light. The emission is due to the 2 E g → 4 A 2g transition. Furthermore, the photoluminescence features intensive ZPL emission and short excitation state lifetime, which is ascribed to the highly distorted coordination environment. The effects of octahedron distortion and the second coordination sphere on the ZPL emission intensity are discussed.