Facile synthesis of self-activated oxyfluorotungstate phosphor with high QE and its thermal quenching

Self-activated phosphors could convert high energy light into visible light from the internal ion groups of host lattice before externally introducing luminescent ions. In this work, we propose a facile route to synthesize self-activated oxyfluorotungstate (Na₂WO₂F₄) phosphor. Excited by the UV light, the emission spectrum covers nearly the entire visible light region. After careful analysis of the first principle calculation results and other sufficient investigation, it is believed that the efficient emission of Na₂WO₂F₄ phosphor comes from the strong parity-allowed absorption of O-2p to W-5d charge transfer band. Moreover, the quantum efficiency of Na₂WO₂F₄ phosphor reaches up to 76% at room temperature. However, the increase of temperature not only lowers the intensity of the PL emission and the quantum efficiency but gives rise to a blue shift of the emission maxima, due to the phonon interaction with the luminescence center in a vibrating crystalline environment.