Combined <i>In Situ</i> Spectroscopies Reveal the Ligand Ordering-Modulated Photoluminescence of Upconverting Nanoparticles
Qingbo Xiao, Yonglan Xi, Jian Wang, Datao Tu, Wenwu You, Xiaomei Ye, Hong Liu, Xueyuan Chen, Hongzhen Lin
Abstract
Clear understanding of the complicated interfacial effect of luminescent nanoparticles is of vital importance for their practical applications. Here, combined in situ spectroscopies based on sum-frequency generation and photoluminescence characterization of lanthanide-doped upconversion nanoparticles are established to distinguish the interfacial quenching effects from ligands and solvents. We provide clear spectroscopic evidence to demonstrate that the ligand conformation significantly influences the extent of luminescence quenching from both the ligands and solvents. Moreover, the ligand disordering induced by an enlarged surface curvature is proved to be one of the major reasons for the notorious size-dependent luminescence quenching of the upconversion nanoparticles. Finally, a conformational entropy-driven strategy is provided to increase the luminescence intensity of the upconversion nanoparticles via capping with mixed layers of oleic and dodecanoic acids. Our findings may open up new avenues for clarifying the complex interfacial photophysical issues regarding inorganic luminescent nanoparticles and promoting their practical applications.