Zero-dimensional metal halides have emerged as a promising class of luminescent materials, attracting significant interest due to their unique electronic structures and fascinating optical characteristics. The photoluminescence (PL) properties of inorganic ternary Cs₃Er_xYb_1-xCl₆ nanocrystals (NCs) were investigated. These alloyed NCs emit dual-band near-infrared (NIR) PL, featuring a sharp NIR-II emission at 1543 nm alongside an NIR-I emission around 987 nm, which originate from the rare earth Er³⁺ and Yb³⁺ ions, respectively. Cs₃Er_0.06Yb_0.94Cl₆ NCs exhibit efficient NIR-II PL with a quantum yield of 2.7% and a lifetime of 157 µs. The enhanced NIR-II PL can be attributed to highly localized excitons, fast energy transfer from Yb³⁺ to Er³⁺ ions and passivation of nonradiative defect states in the Er-Yb alloyed NCs. Given their good penetrability of the NIR-II PL from Er³⁺ ions, a single-component NIR phosphor-converted light-emitting diode (pc-LED) fabricated using Cs₃Er_0.06Yb_0.94Cl₆ NCs demonstrates their potential for future applications in optical communication.