In recent years, the design and application of multifunctional nanocomposites have attracted extensive research interest from scientists. Combining two or more materials through a specific route to construct a new type of material not only overcomes the limitations of a single component itself, but also exhibits dual or multifunctional properties. Rare earth ion-doped upconversion nanoparticles (UCNPs) are favored by researchers in various fields due to their unique physical and chemical properties. UCNPs are combined with other functional materials to achieve synergistic effects, and the resulting nanocomposites show great application potential in biomedicine, anti-counterfeiting and photocatalysis.
Prospects and Challenges of Upconversion Nanoparticles Composites
As one of the most groundbreaking frontier technologies, nanotechnology has promoted the cross-disciplinary integration and development, as well as the design and construction of nanocomposites. In recent years, rare earth ion-doped UCNPs have aroused research interest due to their unique physical and chemical properties. UCNPs combined with other functional materials to construct nanocomposites and achieve synergistic effects can be used as candidate materials with more powerful functions, providing better upconversion luminescence effects and thus exerting greater application potential. It is worth noting that despite the good progress made in the synthesis and application of UCNPs-based nanocomposites, there are still challenges in the following aspects.
The existing synthesis methods based on UCNPs nanocomposites still have many shortcomings. The self-assembly method has the disadvantages of being time-consuming, easy to aggregate, and weakly adsorbed, and the structure is easily destroyed under the action of certain solvents. The in-situ growth method also has certain limitations. The surface of UCNPs must be modified with a polymer with special functional groups to form a precursor, which is used as a nucleation and growth center to induce other nanodots to grow further on the surface. This has prompted us to develop more novel modified materials to ensure that the luminescence of UCNPs will not be excessively quenched, and it can also well ensure that other materials grow uniformly on the surface of UCNPs. The epitaxial growth method often uses toxic and expensive precursors or organic solvents, the product is hydrophobic, and the synthesis temperature is relatively high. Heteroepitaxial growth requires more stringent conditions, and it is difficult to track the reaction process in situ and thus it is difficult to accurately elucidate its reaction mechanism. Therefore, other simple and outstanding synthetic methods still need to be developed and explored.
The biological application research based on UCNPs nanocomposites is still in its infancy, and there are still many problems to be solved. It is of great significance to quantitatively load functional molecules into nanocomposites and achieve controlled release. It cannot be ignored that reducing biological toxicity, improving metabolic efficiency in vivo, and ensuring the repeatability of diagnostic and therapeutic effects are prerequisites for the future use of UCNPs-based nanocomposites in biomedicine.
By combining UCNPs with other luminescent substances, tunable, multicolor, and multimodal luminescent nanocomposites are obtained, which greatly improves the level of fluorescent anti-counterfeiting. Although multiple anti-counterfeiting materials can be used simultaneously to give them multiple security features, the implementation process is complicated, resulting in low production efficiency. This has prompted researchers to develop new nanocomposites with photostability, multiple anti-counterfeiting features and identification methods, and easy processing to promote their practical application.
