<p>Quantum dots (QDs) have emerged as promising candidates for next-generation display owing to their exceptional optoelectronic properties. However, despite substantial advancements in QD synthesis, the blue-emitting QDs, especially heavy-metal-free blue ones, still underperform compared with their red and green counterparts. ZnSeTe QDs offer a viable ecofriendly alternative for blue emissions, but their performance is limited by spectrum broadening (linewidth &gt;20 nm) and structural instability. These issues stem from compositional inhomogeneity, which is primarily induced by Te aggregation during synthesis. Recently, we realized the synthesis of homogeneous quaternary-alloyed ZnSeTeS QDs through a synergistic strategy of reactivity modulation and isoelectronic control. This Protocol enables precise bandgap tuning in the blue spectral region (450–475 nm) by controlling the Te ratio, while ensuring high color purity and stability of QDs. Furthermore, the as-prepared ZnSeTeS QDs exhibit outstanding electroluminescence performance, with a peak external quantum efficiency of 24.7% and half-life of 29,600 h at 100 cd cm⁻², and demonstrate strong potential for applications such as solid-state lighting and bioimaging owing to their high stability and low toxicity. Here we detail a synthesis Protocol for ZnSe_0.94Te_0.03S_0.03/ZnSe/ZnS core/shell/shell QDs via a hot-injection method using zinc carboxylate and anionic phosphine precursor, systematically outlining the design and preparation of precursors and QDs, post treatments (including purifications) and characterization methods, including time-resolved photoluminescence spectroscopy. The entire process typically requires 11–12 h for QD synthesis and 6 h for characterizations, demanding only accessible chemistry knowledge and routine colloidal synthesis techniques.</p>