Illustration of (a) atomic undercoordination induced surface bond contraction (C_z) and potential-well quantum entrapment (QT), and (b) heterocoordination induced interface bond nature alteration and potential well/barrier formation with γ = V_cryst(r, I)/V_cryst(r, B) being the well depth (γ > 1, QT dominance) or barrier height (γ < 1, charge polarization (CP) dominance). (c) Irregular coordination effects on the CL shift from the E(0) to E(B) upon bulk formation and further shift under perturbation. Reprinted with permission from [26, 27]. Copyright 2014, 2020, Springer-Verlag.