Pressure-Tuned Quantum Well Configuration in Two-Dimensional PA₈Pb₅I₁₈ Perovskites for Highly Efficient Yellow Fluorescence

Yellow fluorescent materials (emitting at wavelengths 580–595 nm) offer outstanding functionality for vivid displays, high-density information storage, and high-pressure lighting, especially in white-light-emitting diodes. Currently, the deliberate design of yellow phosphors with high photoluminescence quantum yields (PLQYs) is a developing field. Herein, we report high yellow emission in two-dimensional (2D) halide PA8Pb5I18 (PA = C3H7NH3) perovskite that shows over 80-fold enhancement of their PL under pressure. At an applied pressure of 3.5 GPa, PA8Pb5I18 produces a high PLQY of 77.0% and a color coordinate (0.55, 0.44) closely approaching the standard sodium yellow light (0.575, 0.424). Structural and optical measurements reveal that pressure-induced tilt of the octahedra along the I4–I2 axis is attributable to the deepening of trap states in the quantum well structures, leading to a significant Stokes shift. The resulting more localized excitons have a lower probability of scattering with defects, which results in significant suppression of nonradiative loss and promotion of radiative recombination rate, accounting for the efficient and high-color-purity emission. Our findings represent a deep insight into the photophysical nature of 2D halide perovskites, thus offering a promising strategy for the rational design of high-efficiency yellow phosphors.