Narrow‐Band Nonlinear Near‐Infrared Photodetection Using TiO ₂ ‐Wrapped Multilayer Lanthanide Nanocrystals

Abstract Lanthanide nanocrystals have unique near‐infrared (NIR) absorption and nonlinear upconversion luminescence (UCL) abilities, making them potential candidates for constructing narrow‐band NIR photodetectors. However, significant improvements are still required in NIR absorption, device stability, UCL, and interfacial energy migration efficiency for their commercial applications. Here, to synergistically overcome the above scientific bottlenecks, TiO ₂ @Ln NCs‐980 nano‐assemblies are fabricated by in situ growth of dense TiO ₂ nanocrystals (TiO ₂ NCs) on the surface of NaYbF ₄ @NaYbF ₄ :Gd/Tm@NaYF ₄ nanocrystals (Ln NCs‐980). Ln NCs‐980 are designed with independent NIR absorption, UCL, and inert layers, thereby preventing adverse dissipation and enabling simultaneous upgrades in NIR absorption and UCL efficiency. The ideal energy coupling and spatial distance in nano‐assemblies allow for energy transfer efficiency of ≈ 94% from Ln NCs‐980 to TiO ₂ NCs. A narrow‐band NIR detection electrode constructed with TiO ₂ @Ln NCs‐980 exhibits remarkable selectivity (FWHM ≈ 82 nm), responsivity (≈ 58.5 mA W ⁻¹ ), detectivity (≈ 1.7 × 10 ¹¹ Jones), and stability (over 120 days). In addition, a portable NIR detector is developed by integrating TiO ₂ @Ln NCs‐980 electrode, ammeter, Bluetooth, etc., realizing the application demonstration in collaboration with a smartphone. This work provides a new perspective for the development of lanthanide‐based optoelectronics.