Structural investigation and luminescence of nanocrystalline lanthanide doped NaNbO3 and Na0.5K0.5NbO3

Nd3+ and Eu3+ doped NaNbO3 and Na0.5K0.5NbO3 nanostructured multiferroics (nanoparticles or nanorods) were prepared by a sol–gel route. X-Ray powder diffraction results evidence that the sodium and mixed sodium–potassium niobates show orthorhombic (Pmc21 space group), and monoclinic structure (Pm space group), respectively, confirmed by the Raman spectra. The local structure around the trivalent lanthanides was investigated with Extended X-ray Absorption Fine Structure spectroscopy at the Ln–K edge and luminescence spectroscopy. The Ln3+ ions enter the structure by substituting the alkali metals, with a 12-fold oxygen coordination, and inducing a large amount of static disorder. The visible emission bands of the Eu3+ ions indicate that multiple sites exist for the lanthanide ions, in agreement with the EXAFS results showing the largest amount of static disorder in these samples. A possible indication of clustering of oxygen vacancies around the LnNa″ defect is obtained by VBS calculations.