In this work, DFT calculations were used to study Sc and Ga substitutional doping effects on the structural and optical properties of an AlP nanosheet. Both dopants decrease the bandgap from 2.35 eV to 1.92 eV (Sc, 6%) and 2.19 eV (Ga, 6%). Ga doping reduces the VIP from 2.67 eV to 2.38 eV, while Sc doping increases it to 4.30 eV. Both dopants lower chemical hardness and increase softness. Structurally, Ga preserves the planar hexagonal geometry, while Sc induces significant distortions. Optically, Sc suppresses the dielectric function, refractive index (2.8 to 2.1), and reflectivity (0.51 to 0.21). In contrast, Ga maintains or slightly improves these properties. Therefore, Ga is more compatible with the AlP lattice, while Sc offers a way to raise the VIP while narrowing the bandgap. This study provides a basis for engineering AlP-based 2D materials for optoelectronic devices.