Nonlinear Optical Properties of Stable Cs-doped FAPbBr3 Core@Shell Layered Perovskite Nanocrystals: Superior Temperature Sensing and Flexible Fiber-Based Pure Green LEDs

Organic-inorganic lead halide perovskite nanocrystals (NCs) have evolved as a superior material for various optoelectronic and sensing applications. The ultrapure green emission, high luminescent intensity, narrow emission spectra, and exceptional stability at high temperatures of FAPbBr3 make them suitable for lighting and sensing technologies. Very little research has been explored on photophysical properties, stability improvement, and applications on FA-based NCs. Herein, we represent a room-temperature synthesis of FA1-xCsxPbBr3 NCs, then encapsulated with a layered (OcA)2PbBr4 shell to enhance the NCs' stability and luminescence intensity. Though 10% Cs-doped FAPbBr3 NCs showed maximum emission intensity, we coated (OcA)2PbBr4 shells around 20% Cs-doped FAPbBr3 NCs for their highest stability. The nonlinear optical properties of the NCs dominated by the thermal lens effect reveal reverse saturable absorption and self-focusing effects with higher χ(3) values in the order of 10-6 e.s.u. The core@shell NCs were tested as temperature sensors, demonstrating a maximum relative sensitivity of 3.31 %-K-1. Further, these NCs were embedded in PMMA microfibers to improve flexibility and stability. These fluorescent microfibers offered excellent water stability for about four months while dipped in water. Finally, the fibers were tested as a fluorescent source to fabricate down-converted green LED, which unveils a CCT value of ~8161 K and a maximum efficiency of ~85 Lm/W. This research unlocks new possibilities for FA-based NCs for efficient temperature sensing, flexible futuristic displays, and optical limiting applications.