Improving　polarizability　is　an　important　strategy　for　designing　high-performance　mid-infrared　(mid-IR)　nonlinear　optical　(NLO)　materials.　The　substitution　of　equivalent　or　aliovalent　atoms　can　manipulate　the　polarizability　by　adjusting　the　symmetry　of　the　polyhedron.　Herein,　the　Li+　and　Cd2+　are　introduced　into　the　Cu3PS4　as　the　equivalent　and　aliovalent　dopants　for　the　Cu　site.　As　a　result,　Li+　can　significantly　improve　the　bandgap　(Eg)　of　LixCu3−xPS4　from　2.38　to　2.88 eV,　leading　to　a　higher　laser-induced　damage　threshold　(LIDT)　of　4.9　times　than　AgGaS2　(AGS)　with　a　comparable　second　harmonic　generation　(SHG)　response　of　AGS　(26−45 µm).　Interestingly,　Cd2+　can　improve　the　SHG　response　and　enlarge　the　Eg　simultaneously.　As　a　result,　Cd0.4Cu2.2PS4　has　a　large　SHG　response　of　10　×　AGS　at　2050 nm　(26−45 µm)　and　a　LIDT　of　2.6　×　AGS.　Theoretical　calculations　reveal　that　lattice　vacancies　induced　by　Cd2+　significantly　boost　polarizability　compared　to　LixCu3−xPS4　with　no　vacancy,　leading　to　a　strong　NLO　response.　©　2024　Wiley-VCH　GmbH.