Abstract: In recent years, luminescent materials in near-infrared fluorescence conversion light-emitting diodes (NIR pc-LEDs) attract increasing attention. However, most NIR fluorescent materials exhibit low photoluminescence quantum yield (PLQY), which is unfavorable for the fabrication of NIR pc-LEDs. Therefore, this work synthesizes high-quality Cu–In–Ga–S (CIGS) @ZnS quantum dots (QDs) as near-infrared fluorescent materials using a one-pot method. By changing the molar content of Ga, the photoluminescence (PL) spectrum is tunable in the range of 800 nm to 930 nm. After coating with a ZnS shell, the PLQY increases from 42.3% for CIGS QDs to 92.3% for CIGS@ZnS QDs. The PL spectra and PL decay curves under varying excitation power indicate that the CIGS and CIGS@ZnS QDs primarily emit light through the mechanism of donor-acceptor pair (DAP) recombination. Temperature-dependent PL tests on CIGS and CIGS@ZnS QDs reveal that the ZnS shell suppresses the electron-phonon interactions within the QDs, leading to an increase in radiative recombination of charge carriers and thus enhancing the PLQY. A 1.5 mm thick near-infrared composite film, prepared by blending polymethyl methacrylate (PMMA) with CIGS@ZnS QDs, combined with commercial blue LED chips, results in NIR pc-LEDs that exhibit the highest optical power and a greater proportion of near-infrared light in the emission spectrum.