Relation of Crystallinity and Fluorescent Properties of LaF3:Nd3+ Nanoparticles Synthesized with Different Water-Based Techniques

We use two water based synthetic approaches to LaF3:Nd3+ nanoparticles (NPs), hydrothermal microwave treatment (HTMW) and co-precipitation (CO) technique, with different temperature of the reaction mixture to study the correlation between the degree of crystallinity of LaF3:Nd3+ NPs and their fluorescence properties. We showed that the fluorescence spectra and quenching kinetics can be a powerful tool to reveal the crystal lattice defects, namely agglomerations of the dopant ions (Nd3+) and the OH- positioned in the volume of the doped NPs. We found that reduced number of such crystal lattice defects as Nd3+ pairs and clusters and the OH groups in the volume of the HTMW NPs leads to much higher fluorescence brightness than for CO NPs. The higher temperature of reaction mixture during HTMW synthesis results in better crystallinity and much higher fluorescence brightness of the produced NPs. But we believe that these results could be applied more generally to the development of synthetic strategies for bright fluorescent NPs. In sum, it's not the condition of NPs surface, but the degree of their crystallinity should be a major concern while choosing the synthetic path, as it generally predetermines their fluorescent properties.