Structural characterization and photoluminescence behavior of pure and doped potassium strontium niobates ceramics with tetragonal tungsten-bronze structure

KSr2Nb5O15 and K1.2Sr1.6Ln0.2Nb5O15 (Ln=La, Pr, and Nd) were synthesized by the Pechini method and calcined at 1373 K for 10 h under air atmosphere. Rietveld refinements indicated the presence of structural defects in both KSN and KSN-Ln, especially distortions in O-Nb-O and Nb-O-Nb bonds. Modifications in bond distances of [NbO6] clusters were also confirmed by Raman spectroscopy. Ultraviolet-visible absorption spectra and photoluminescence profiles were influenced by lanthanide atoms in the band structure of modified KSN materials, creating new defects and intermediary energy levels within the band gap.