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

Abstract

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 C 2 symmetry, which helps remove the parity forbidden f–f transitions.

Effects of Defect Density on Optical Properties Using Correlative Cathodoluminescence and Transmission Electron Microscopy Measurements on Identical PrNbO4Particles

“…Because higher emission lines are observed for the twinned areas, we believe that these crystal defects are perturbing f–f transitions, resulting in increased intensity. Based on these results and our recent findings published in ref , the high amount of Pr in addition to the presence of defects in PrNbO 4 makes these particles excellent luminescent materials. Moreover, we showed with our multitechnique approach that higher density of the twins leads to the strongest luminescence brightness, and therefore they are better candidates to be used in optical applications.…”

“…This reaction was done to obtain particles with the nominal formula Pr x K 1– x Ca 2– x Nb 3 O 10 . X-ray diffraction reported in ref showed the formation of two phases, namely, Pr 3+ :Ca 2 Nb 2 O 7 and PrNbO 4 . PrNbO 4 particles were produced due to the excess of Pr.…”

“…Synthesis of the polycrystalline samples was done by using a solid-state route with protocols altered from the literature . The optimum amount, described in ref , of K 2 CO 3 , CaCO 3 , and Nb 2 O 5 was mixed together with Pr 6 O 11 . Afterward, to complete the reaction progress, various temperatures between 1100 and 1300 °C were used to anneal the mixture.…”

“…In our recent work, 16 we compared two types of complex niobates with different praseodymium (Pr) concentration and reported that PrNbO 4 with monoclinic structure has enhanced luminescence compared to the cubic Pr 3+ :Ca 2 Nb 2 O 7 . In this study, we focus on PrNbO 4 but with the emphasis on its crystal defects (such as twins) and the local differences in defect density to understand the excellent luminescent properties of these materials.…”

Combined structural analysis and cathodoluminescence investigations of single Pr3+-doped Ca2Nb3O10 nanosheets

“…The optical properties of individual nanosheets with different thicknesses are correlated to their crystal structure and chemical composition obtained via transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). We found that due to the lower Pr content observed in the nanosheets compared to bulk particles 10 , 11 , different luminescence properties are observed.…”