Rare Earth Ion-Doped Upconversion Nanocrystals: Synthesis and Surface Modification

Abstract

The unique luminescent properties exhibited by rare earth ion-doped upconversion nanocrystals (UCNPs), such as long lifetime, narrow emission line, high color purity, and high resistance to photobleaching, have made them widely used in many areas, including but not limited to high-resolution displays, new-generation information technology, optical communication, bioimaging, and therapy. However, the inherent upconversion luminescent properties of UCNPs are influenced by various parameters, including the size, shape, crystal structure, and chemical composition of the UCNPs, and even the chosen synthesis process and the surfactant molecules used. This review will provide a complete summary on the synthesis methods and the surface modification strategies of UCNPs reported so far. Firstly, we summarize the synthesis methodologies developed in the past decades, such as thermal decomposition, thermal coprecipitation, hydro/solvothermal, sol-gel, combustion, and microwave synthesis. In the second part, five main streams of surface modification strategies for converting hydrophobic UCNPs into hydrophilic ones are elaborated. Finally, we consider the likely directions of the future development and challenges of the synthesis and surface modification, such as the large-scale production and actual applications, stability, and so on, of the UCNPs.

Shaping Luminescent Properties of Yb3+ and Ho3+ Co‐Doped Upconverting Core–Shell β‐NaYF4 Nanoparticles by Dopant Distribution and Spacing

“…Despite numerous possible applications of UCNPs in biotechnology, nanomedicine, biophotonics, and photovoltaics, there are still some drawbacks to overcome. Challenges to address include the reproducible and predictable preparation of high color purity UCNPs for multiplexed imaging, as well as the low absorption cross sections of the lanthanide ions and the low efficiency of the upconversion (UC) processes, especially for small UCNPs with sizes < 30 nm, diminishing particle brightness and hence, limits of detection. The latter two factors are particularly important for biological and biomedical applications, which require nanoscale optical agents with sizes below 50 nm to assure at least partial physical compatibility with the size of biologically relevant structures and biomolecules.…”

Fabrication of a LRET-based upconverting hybrid nanocomposite for turn-on sensing of H2O2and glucose

“…[29][30][31][32][33][34][35][36] In contrast to traditional fluorescence material, UCNPs possess remarkable advantages, such as large anti-Stokes shifts, negligible light scattering background, high resistance to photobleaching and non auto-fluorescence from biosamples. [29][30][31][32][33][34][35][36] In contrast to traditional fluorescence material, UCNPs possess remarkable advantages, such as large anti-Stokes shifts, negligible light scattering background, high resistance to photobleaching and non auto-fluorescence from biosamples.…”

Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications

“…It is a wet‐chemical method which involves rapid hydrolysis of a molecular precursor followed by polycondensation reactions. After drying, the resulting gel is subjected to calcination increase crystallinity . Sol–gel processing is influenced by several parameters such as pH, the concentration of reactants, temperature, and presence of additives.…”