Structural and photoluminescence properties of stannate based displaced pyrochlore-type red phosphors: Ca3−xSn3Nb2O14:xEu3+

Abstract

New stannate based displaced pyrochlore-type red phosphors, Ca_3−xSn₃Nb₂O₁₄:xEu³⁺, were prepared via a conventional solid state method. The influence of partial occupancy of Sn in both A and B sites of the pyrochlore-type oxides on the photoluminescence properties was studied using powder X-ray diffraction, FT-Raman, transmission electron microscopy, scanning electron microscopy with energy dispersive spectrometry, UV-visible absorption spectroscopy, and photoluminescence excitation and emission spectra with lifetime measurements. The structural analysis establishes that these oxides belong to a cubic displaced pyrochlore type structure with a space group Fdm. These phosphors exhibit strong absorptions at near UV and blue wavelength regions and emit intense multiband emissions due to Eu^{3+ 5}D₀–⁷F_{0, 1, 2} transitions. The absence of characteristic MD transition splitting points out that local cation disorder exists in this type of displaced pyrochlores, reducing the D_3d inversion symmetry, which is not evidenced by such disorder in the X-ray diffraction analysis. The unusual forbidden intense sharp ⁵D₀–⁷F₀ transition indicates single site occupancy of Eu³⁺ with a narrower range of bonding environment, preventing the cluster formation. This is supported by the stable ⁵D₀ lifetime with Eu³⁺ concentration. The Judd–Ofelt intensity parameter assessment corroborates these results. The CIE color coordinates of these phosphors were found to be (0.60, 0.40), which are close to the NTSC standard values (0.67, 0.33) for a potential red phosphor.