Cs₃Cu₂X₅-based lead-free material (X = Cl, Br, and I) nanocrystals (NCs) are promising eco-friendly materials for various optoelectronic applications. Although manganese (Mn²⁺) ion doping into Cs₃Cu₂X₅ may widen the emission color gamut, incorporating them is challenging because of the robust tetrahedral [CuX₄] and triangular [CuX₃] structures. This paper addresses this challenge using a lattice engineering strategy, which induces appropriate lattice shrinkage by replacing I⁻ with Cl⁻ in the Cs₃Cu₂I₅ NC structure. The promotion effect of Cl⁻ substitution on the Mn²⁺ doping is confirmed by structural and chemical analysis, indicating the formation of highly crystalline NCs. The Mn-doping modifies the electronic structures of Cs₃Cu₂X₅ by reducing the band gap energy and forming effective energy transition pathways. The emission range of the NCs is expanded from blue to orange and finally manifest full-color gamut white light emission. The continuous broad spectrum is attributed to the combined blue emission of self-trapped excitons and the yellow-orange emission of the Mn²⁺ d–d energy transition. A white light-emitting diode with Mn-doped Cs₃Cu₂X₅ NCs as a color conversion layer exhibit stable white emission with CIE coordinates of (0.34, 0.32) and a correlated color temperature of 5010 K, closely matching daylight conditions and is applied as an intelligent artificial sunlight.