Correlation between Structural Studies and the Cathodoluminescence of Individual Complex Niobate Particles

Lanthanide-doped semiconductors and the mechanism of energy transfer from host to lanthanide ions have always been a topic of great interest. In this study, we underline the effect of the lanthanide ions' surroundings on the width of the emission lines. We show that different crystal structures and lattice defects within the crystal lead to different atomic coordinates of the ion. In this work, complex niobates synthesized in a solid-state route were investigated. Because of the micron size of the particles, scanning electron microscopy in addition to energy dispersive X-ray spectroscopy were used to study the morphology and chemical composition, respectively. Moreover, the correlation between chemical composition and the crystal structure of the particles was investigated using transmission electron microscopy. These analyses show the presence of two phases with different chemical compositions and crystal structures, namely PrNbO4 and Pr3+:Ca2Nb2O7. We studied the optical properties of both phases using a cathodoluminescence spectrometer attached to the scanning electron microscope. In the cathodoluminescence spectra of PrNbO4, that is, for particles with higher Pr content, brighter emission lines were observed. Possible causes for the improved luminescent properties of PrNbO4 are the higher amounts of Pr as both K and Ca atoms are substituted in the initial KCa2Nb3O10 powder by Pr; therefore, Pr3+ ions are surrounded by Nb and O only. As a result, Pr3+ ions occupy the sites with C2 symmetry, which helps remove the parity forbidden f–f transitions.