Abstract: White light-emitting diodes (WLEDs) are promising alternatives to traditional lighting sources owing to their energy efficiency, compact design, long lifespan, and environmental benefits. However, the practical application of quantum dots (QDs) in WLEDs faces significant challenges, including low luminous efficiency and thermal quenching. Herein, we propose a strategy to obtain QDs with excellent photoluminescence properties and thermal stability by building the well-designed Zn-carboxylate-based porous coordination polymer (MOF-5) and embedding AgInS₂ (AIS) QD nanocomposite structures via a microwave-assisted organic synthesis method; the resulting nanocomposites are suitable for practical adoption in warm WLED devices. The MOF-5 metal–organic framework provides spatial and electronic isolation for the QDs, effectively preventing fluorescence quenching. Moreover, it simultaneously increases the emission efficiency by generating a ZnS layer that passivates the surface defects and reduces non-radiative recombination, thereby improving the fluorescence quantum yield (PLQY) and thermal stability. The AIS@ZnS@MOF-5 nanocomposite exhibits a 12.6-fold increase in thermal stability and a 3.45-fold enhancement in the PLQY (44.88%). The nanocomposite is further integrated with commercial green-emitting (Ba,Sr)Si₂O₂N₂:Eu²⁺ phosphors as a color-conversion layer in WLEDs. The resulting WLED device emits warm white light with a color rendering index of 83.5, a correlated color temperature of 3638 K, and a luminous efficiency of 83.42 lm/W. This strategy effectively enhances both the luminescence efficiency and stability of AIS QDs, serving as a significant step toward the development of QD-based WLEDs for practical applications.