Nonlinear optical properties of stable Cs-doped FAPbBr3 core@shell layered perovskite nanocrystals: superior temperature sensing and flexible fiber-based pure green LEDs†

Abstract

Organic–inorganic lead halide perovskite nanocrystals (NCs) have evolved as superior materials for various optoelectronic and sensing applications. The ultrapure green emission, high luminescent intensity, narrow emission spectra, and exceptional stability at high temperatures of FAPbBr₃ NCs make them suitable for lighting and sensing technologies. However, little research has been conducted on the photophysical properties, stability improvement, and applications of FA-based NCs. Herein, we present the room-temperature synthesis of FA_1−xCs_xPbBr₃ NCs, which were subsequently encapsulated with a layered (OcA)₂PbBr₄ shell to enhance their stability and luminescence intensity. Although the 10% Cs-doped FAPbBr₃ NCs showed the maximum emission intensity, we coated (OcA)₂PbBr₄ shells around the 20% Cs-doped FAPbBr₃ NCs owing to their highest stability. The nonlinear optical properties of the NCs dominated by the thermal lens effect revealed 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 their flexibility and stability. The fluorescent microfibers exhibited excellent water stability for about four months when dipped in water. Finally, the fibers were tested as fluorescent sources to fabricate a down-converted green LED, which exhibited a CCT value of ∼8161 K and maximum efficiency of ∼85 Lm W⁻¹. This research unlocks new possibilities for FA-based NCs for efficient temperature sensing, flexible futuristic displays, and optical limiting applications.