Ionic conductivity and optical properties of self-activated phosphor CsYP2O7

Abstract Pyrophosphates are interesting compounds as optical materials, ionic conductors, solid electrolytes, battery electrodes, solid-state lasers and active layer for sensors. In this context, the compound CsYP 2 O 7 has been synthesized by the solid-state reaction method. The X-ray powder diffraction at room temperature confirmed the phase formation of the synthesized compound in the monoclinic phase. The composition and morphology were performed by energy dispersive spectroscopy coupled with scanning electron microscope . The optical properties of the compound were studied by UV–Vis absorption spectroscopy. By direct investigation of the UV absorption measurements and using the Tauc model, we have found that the direct optical band gap is equal to 3.7eV. Two of the relaxation mechanisms were clearly identified from Nyquist plots and modulus analysis, which can be discerned to both grain and grain boundary contributions effect. The obtained results were analyzed by fitting the experimental data to an equivalent circuit model.Bulk resistance and grain boundary resistance decreased with the increase of temperature, which confirmed negative temperature coefficient of resistance behavior. The same values of activation energies obtained from the impedance (0.43 eV ) and hopping frequency (0.42 eV),prove that the transport happens through an ion hopping mechanism dominated by the motion of the Cs + cations in the structure of the CsYP 2 O 7 material. The results confirm tha the synthesized compound is suitable for catalysis and optoelectronic applications.