Multilayer Core–Shell Upconversion Nanoparticles for Dynamic Dual‐Color Emission Switching and High‐Sensitivity Temperature Sensing in Information Security

Abstract Information security and temperature sensing play vital roles in various areas such as financial transactions, product authentication, and privacy protection. However, integrating precise control in information security technologies with highly sensitive temperature sensing remains a significant challenge. Here, a multilayer core–shell upconversion nanoparticle (UCNP) system is presented that enables dynamic dual‐color emission switching and highly sensitive temperature sensing through controlled energy transfer mechanisms. By tuning the excitation wavelength, power density, and pulse width, the system exhibits a green‐to‐blue emission transition with multimodal tunability. Using fluorescence intensity ratio techniques, maximum relative sensitivity of 1.85% K −1 , demonstrating superior temperature detection performance is achieved. Furthermore, the tunable multicolor emission properties of UCNPs enable diverse applications in information security, including dynamic pattern recognition, Morse code encryption, and quick response code‐based anti‐counterfeiting. This research not only broadens the application scope of UCNPs in security and environmental monitoring but also offers perspectives on the design of multifunctional optical materials.