Multi-Color Luminescence Transition of Upconversion Nanocrystals via Crystal Phase Control with SiO2 for High Temperature Thermal Labels

Behavioral biometric optical tactile sensor for instantaneous decoupling of dynamic touch signals in real time

Decoupling dynamic touch signals in the optical tactile sensors is highly desired for behavioral tactile applications yet challenging because typical optical sensors mostly measure only static normal force and use imprecise multi-image averaging for dynamic force sensing. Here, we report a highly sensitive upconversion nanocrystals-based behavioral biometric optical tactile sensor that instantaneously and quantitatively decomposes dynamic touch signals into individual components of vertical normal and lateral shear force from a single image in real-time. By mimicking the sensory architecture of human skin, the unique luminescence signal obtained is axisymmetric for static normal forces and non-axisymmetric for dynamic shear forces. Our sensor demonstrates high spatio-temporal screening of small objects and recognizes fingerprints for authentication with high spatial-temporal resolution. Using a dynamic force discrimination machine learning framework, we realized a Braille-to-Speech translation system and a next-generation dynamic biometric recognition system for handwriting.

Random fractal-enabled physical unclonable functions with dynamic AI authentication

A physical unclonable function (PUF) is a foundation of anti-counterfeiting processes due to its inherent uniqueness. However, the self-limitation of conventional graphical/spectral PUFs in materials often makes it difficult to have both high code flexibility and high environmental stability in practice. In this study, we propose a universal, fractal-guided film annealing strategy to realize the random Au network-based PUFs that can be designed on demand in complexity, enabling the tags' intrinsic uniqueness and stability. A dynamic deep learning-based authentication system with an expandable database is built to identify and trace the PUFs, achieving an efficient and reliable authentication with 0% "false positives". Based on the roughening-enabled plasmonic network platform, Raman-based chemical encoding is conceptionally demonstrated, showing the potential for improvements in security. The configurable tags in mass production can serve as competitive PUF carriers for high-level anti-counterfeiting and data encryption.

An overview of boosting lanthanide upconversion luminescence through chemical methods and physical strategies

Lanthanide-doped upconversion nanoparticles have attracted extensive research interest due to their promising applications in various fields.

Programmable multilayer printing of a mechanically-tunable 3D hydrogel co-culture system for high-throughput investigation of complex cellular behavior

Hydrogels are widely used as a 3D cell culture platform, as they can be tailored to provide suitable microenvironments to induce cellular phenotypes with physiological significance. Hydrogels are especially deemed attractive as a co-culture platform, in which two or more different types of cells are cultured together in close proximity, since the spatial distribution of different cell types can be rendered possible by advanced microfabrication schemes. Herein, programmable multilayer photolithography is employed to develop a 3D hydrogel-based co-culture system in an efficient and scalable manner, which consists of an inner microgel array containing one cell type covered by an outer hydrogel overlay containing another cell type. In particular, the mechanical properties of microgel array and hydrogel overlay are independently controlled in a wide range, with elastic moduli ranging from 1.7 to 31.6 kPa, allowing the high-throughput investigation of both individual hydrogel mechanics and mechanical gradients generated at their interface. Utilizing this system, phenotypical changes (i.e. proliferation, spheroid formation and Mφ polarization) of macrophages encapsulated in microgel array, in response to complex mechanical microenvironment and co-cultured fibroblasts, are comprehensively explored.

Overcoming thermal quenching in upconversion nanoparticles

Thermal quenching that is characterized by loss of light emission with increasing temperature is widely observed in luminescent materials including upconversion nanoparticles, causing problems in technological applications such as lighting, displays, and imaging. Because upconversion processes involve extensive intra-particle energy transfer that is temperature dependent, methods have been established to fight against thermal quenching in upconversion nanoparticles by engineering the energy transfer routes. In this minireview, we discuss the origin of thermal quenching and the role of energy transfer in thermal quenching. Accordingly, recent efforts in overcoming thermal quenching of upconversion are summarized.

Thermal enhancement of upconversion emission in nanocrystals: a comprehensive summary

Luminescence thermal stability is a major figure of merit of lanthanide-doped nanoparticles playing an essential role in determining their potential applications in advanced optics. Unfortunately, considering the intensification of multiple electron-vibration interactions as temperature increases, luminescence thermal quenching of lanthanide-doped materials is generally considered to be inevitable. Recently, the emergence of thermally enhanced upconversion luminescence in lanthanide-doped nanoparticles seemed to challenge this stereotype, and the research on this topic rapidly aroused wide attention. While considerable efforts have been made to explore the origin of this phenomenon, the key mechanism of luminescence enhancement is still under debate. Here, to sort out the context of this intriguing finding, the reported results on this exciting topic are reviewed, and the corresponding enhancement mechanisms as proposed by different researchers are summarized. Detailed analyses are provided to evaluate the contribution of the most believed "surface-attached moisture desorption" process on the overall luminescence enhancement of lanthanide-doped nanoparticles at elevated temperatures. The impacts of other surface-related processes and shell passivation on the luminescence behaviour of the lanthanide-doped materials are also elaborated. Lack of standardization in the reported data and the absence of important experimental information, which greatly hinders the cross-checking and reanalysis of the results, is emphasized as well. On the foundation of these discussions, it is realized that the thermal-induced luminescence enhancement is a form of recovery process against the strong luminescence quenching in the system, and the enhancement degree is closely associated with the extent of luminescence loss induced by various quenching effects beforehand.

Crystal engineering of nanomaterials: current insights and prospects

Nanocrystal engineering has evolved into a dynamic research area over the past few decades but is not properly defined. Here, we present select examples to highlight the diverse aspects of crystal engineering applied on inorganic nanomaterials.