This study uses precation exchange reactions to gauge terbium emission enhancement through cosensitization effects in Zn(Tb)S NPs that are modified postsynthetically by Pb²⁺, Sn²⁺, Sn⁴⁺, Sb³⁺, Bi³⁺, In³⁺, and Tl⁺ to generate Zn(Tb)S/M (Mⁿ⁺ = Pb²⁺, Sn²⁺, Sn⁴⁺, Sb³⁺, Bi³⁺, In³⁺, and Tl⁺) NPs. Mⁿ⁺-induced cosensitization of Tb³⁺ emission is observed in the Sn²⁺, Pb²⁺, and Sb³⁺-containing NPs, with [Zn(Tb)S]: [Mⁿ⁺] = 1:10^–2. Tl⁺ produces similar sensitized emission in the NPs, however, only when the amount of these cations is in stoichiometric excess. On the contrary, the NPs with Sn⁴⁺, Bi³⁺, and In³⁺ do not provide such sensitization. The electronic cross-talk in these codopant(s) leading to cosensitization effects is correlated with the placement of codopant energy levels in the host NPs from the density functional theory calculations. The results collectively offer a rationale for predicting the appropriate codopant–Tb³⁺ (donor–acceptor) pair to achieve favorable electronic interactions that cosensitize Tb³⁺ emission in Zn(Tb)S/M NPs. Such Tb³⁺ emission enhancements create inroads for applications in sensing and imaging.