Role of electronegativity on the crystal field splitting of Eu3+ manifold in pyrochlore-type oxides, Ca3M3Nb2O14 (M = Ti and Sn)

Abstract

In this work, the influence of partial substitution of tetravalent cations like Ti and Sn on both A and B sites of the pyrochlore type Ca3M3Nb2O14:0.15Eu3+ (M = Ti and Sn) red phosphors on the photoluminescence properties was studied. In this attempt, the compositions of the formula Ca3Sn3-xTixNb2O14:0.15Eu3+ (x = 0, 1.5 and 3) and Ca3Ti3Nb2O14:xEu3+ (x = 0.05–0.20) phosphors were prepared via the conventional ceramic route and characterized for their structure, morphology and photoluminescence properties through various advanced techniques. Powder XRD analysis of these phosphors confirm the formation of the pyrochlore-type structure with partial occupation of Ti/Sn cations on the A site. Thus the mixing of Ti/Sn ions on the A site revealed the role of electronegativity of these ions on the photoluminescence properties of these phosphors. The full width half maximum (fwhm) of the charge transfer band in titanate phosphor is more compared to that of stannates and charge transfer band is relatively located at longer wavelength (333 nm) in titanate phosphors compared to stannate system The splitting of characteristic Eu3+ manifold is smaller in titanates relative to the stannate phosphors. Further, the fwhm of 5D0-7F2 electric dipole transition is observed to be narrow for titanium substituted compositions which is ascribed to the difference in bonding environment of Ti and Sn in the host lattice. The titanate phosphors exhibit intense sharp narrow red emissions due to 5D0–7F2 transitions of Eu3+ ions with higher asymmetric ratio. The presence of the single sharp 5D0-7F1 magnetic dipole transition in both systems without splitting confirms the loss of pyrochlore D3d symmetry around the Eu3+ ions. These results imply that displaced pyrochlore system offers a lot of opportunities to manipulate the luminescence properties.