Interstitial TM–P Pairing in P3-Coordinated Wide-Gap Quantum Dots: Spin-Selective Insulating States and Enhanced Hyperpolarizability

Abstract

The variation in electronic, magnetic, and nonlinear optoelectronic properties due to interstitial doping on group-12 based single-atom thick ternary metal-phosphorus-chalcogenide quantum dots (MPC QDs) have been studied with density functional theory computations. This novel doping strategy intended to examine the impacts of P3–TM hybridizations in surface-bound region and how it systematically regulates multifunctional behavior of these nanoflakes. It is found that the placement of a transition metal (TM) atom at a hollow site, in proximity to the substituted phosphorus, leads to localized magnetic moments in these honeycomb-shaped nanoflakes. Moreover, a few configurations retain their nonmagnetic character despite the interstitial coordination (spin compensation), while nonlocal chalcogen coordination within the host framework modulates the overall magneto-electronic response. The spin-polarization can be tuned to achieve specific magnetic ordering with S = 1, 3/2, 2, and 3, confirming constrained spatial extent of stable spin density around the dopant. Pristine MPCQDshaveenergy gaps of 2.7–7.37 eV, which increase for Zn/Cd and decrease for Hg with chalcogens, while Co-, Ni-, Mn-, or V-doped cases range from 4.53 to 9.10 eV (E↑ g) and from 3.89 to 7.13 eV (E↓ g). Moreover, linear polarizability increases with chalcogens (S to Te) for pristine and ternary cases, while interstitial cases show enhanced static first-hyperpolarizability due to co-doping-induced charge asymmetry. Overall, understanding doping-induced local hybridization in wide-gap nanoflakes, which gives rise to proximal magnetic moments with controllable HOMO-LUMO distributions and enhanced hyper(polarizability), enables the effort to engineer spin-filtering devices, spin-based quantum computation, second-harmonic generation (SHG), and electro-optic modulation.