A reverse coprecipitation route for preparing Na2WO2F4:Mn4+ phosphor with high yield

Abstract

For the coprecipitation preparation of the Na2WO2F4:Mn4+ phosphor, we propose a new reverse approach, i.e., adding the precursor solution into a precipitant, which efficiently induces the precipitation of the targeted composition with much higher yield than a conventional forward approach. NaHF2 occurred as a secondary phase due to the high HF concentration in the precursor solution but was successfully avoided by varying the precipitant from alcohols to acetic acid. The as-precipitated Na2WO2F4:Mn4+ phosphor exhibits strong zero phonon line emission (ZPL) at 619 nm; the ZPL/ν6 (Stokes) intensity ratio varies from 137% to 73%, depending on the type and amount of the precipitant, the reason for which is ascribed mainly to the nonstoichiometry of Na+. This reverse coprecipitation approach could be applicable to prepare any other oxyfluoride compositions with considerable solubility.