Sol-gel synthesis, crystal structure and luminescence properties of Eu3+ doped double perovskite molybdates NaCaBi1−xEuxMoO6 (x = 0–0.27)

Abstract

Sodium and calcium containing bismuth molybdates of double perovskite structured NaCaBi1−xEuxMoO6 (x = 0.0–0.27) were prepared by a sol-gel combustion method. The samples were finally sintered at 500, 600 & 700 °C/5 h each and characterized by using powder X-ray diffraction (XRD), UV–Visible absorption and fluorescence spectroscopy. The powder XRD patterns indicated a monoclinic phase initially for x = 0 to 0.09 and then a mix of monoclinic and triclinic phases for x = 0.12 to 0.18. For the remaining compositions, i.e. for x = 0.21–0.27 the samples crystallized in triclinic phase only. A corresponding change of lattice parameters and peak positions were observed in powder XRD patterns as the Eu3+ concentration was increased. The powder samples sintered at 700 °C /5 h were excited at 395, 465 & 540 nm and their corresponding emission spectra showed major peaks in the vicinity of 595 & 614 nm for all the excitation wavelengths. The Eu3+ concentration of x = 0.12 gave highest red light emission intensity, related to the transition 5D0–7F2. The morphology of powders showed clear and characteristic nano-flake like structure. The color rendering index (CRI) coordinates of all the samples were calculated and showed values close to National Television Standards Committee (NTSC) coordinates of pure red phosphor showing promise for phosphor converted -white light emitting diodes (pc-WLEDs).