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

Abstract

Oxyfluorides activated with Mn4+ 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 K2WO2F4·H2O activated with Mn4+ were synthesized by using a coprecipitation method. The structural parameters and atomic coordinations of K2WO2F4·H2O were determined by both refinement and calculation. K2WO2F4·H2O crystallizes in the monoclinic crystal system with C2/m group space. The unit cell could be considered as a stack of KWO2F4 slices with another K+ ion and H2O molecule in the interstitial. The morphology and photoluminescence properties of K2WO2F4·H2O: Mn4+ were studied as a function of Mn4+ concentration. It is revealed that the microcrystalline shows highly orientational preferred growth. Mn4+ shows bright red emission upon the excitation of blue light. The emission is due to the 2Eg→4A2g 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.