Theoretical Study on Narrow-Band White Quantum Dot LEDs Based on Asymmetric F-P Microcavities

White LEDs are widely used in fields such as lighting and display. However, existing white light devices suffer from excessively broad emission spectra full width at half maximum (FWHM) and severe leakage of pump blue light. Hence, this study proposes a theoretical design for an ultra-narrow-band white LEDs based on an asymmetric Fabry-Pérot (F-P) microcavity. The microcavity employs a dual-DBR configuration with asymmetric optical responses: the bottom DBRs utilize a ZnS/MgF2 (dL/2-dH-dL/2)5 stack, providing a low reflectance of ~20% at 457 nm for efficient blue light transmission and quantum dot excitation; conversely, the final device incorporating top DBRs with a TiO2/MgF2 (dH/2-dL-dH/2)4-stacked structure achieved a high reflectivity of approximately 89% at 457 nm, effectively decreasing the excessive blue light in the output spectrum. The intermediate emissive layer uses polymethyl methacrylate (PMMA) as the quantum dot host. By precisely tuning the cavity thickness, the resonant modes of the F-P microcavity—specifically the fourth-order (626 nm) and fifth-order (534 nm)—are aligned with the emission peaks of the red and green quantum dots, respectively. Simulation results demonstrate that the structure leverages the cavity filtering effect to compress the FWHM of the red and green emissions from initial values of 36.5 nm and 29.8 nm down to 2.2 nm and 1.9 nm, respectively, representing an order-of-magnitude improvement in color purity. Through the co-optimization of the top-DBR’s central wavelength, cavity optical thickness, and the doping ratio of red/green quantum dots, standard white light emission with CIE coordinates of (0.32, 0.33) was achieved, accompanied by emission efficiencies of 6.3% (green) and 22.3% (red) for the QDs. However, strict manufacturing tolerances and narrow observation angles limit the applicability of the device. This work provides theoretical research for developing white light sources.