Influence of copper substitution on the electronic structure and magnetic properties of SnO2 quantum dots: An experimental and DFT insights

Diluted magnetic semiconductor quantum dots exhibit integrated electronic and magnetic properties, making them suitable for spintronics and optoelectronics device applications. Although copper-doped SnO 2 nanostructures showing magnetic properties have been widely studied, the ferromagnetism and magnetic origin of copper-doped SnO 2 at the quantum dot scale remain poorly understood. Herein, we report the influence of non-magnetic copper incorporation (2% and 4% Cu) and the decisive contribution of oxygen vacancies on the magnetic properties and electronic structure of copper-substituted SnO 2 quantum dots prepared via the hydrothermal method. Powder X-ray diffraction and characteristic Raman modes at 632 (A 1 g ), 774 (B 2 g ), and 477 (E g ) cm −1 revealed a monophase tetragonal rutile structure. UV-Visible optical absorption spectroscopy indicated a blue-shifted band gap of 3.64 and 3.70 eV for 2% Cu and 4% Cu-doped SnO 2 quantum dots, respectively, demonstrating quantum-size effects. Magnetic studies showed strong room-temperature ferromagnetism at the quantum-dot scale, attributed to the bound magnetic polaron mechanism. Notably, 2% Cu-doped SnO 2 quantum dots exhibited a larger magnetic saturation of 3.4 × 10 −3 emu/g, while 4% Cu-doped SnO 2 quantum dots showed a higher coercivity of 457.2 Oe. Spin-polarized density functional theory substantiated that the emergence of new hybridized Cu 3d–O 2p states in the range −2.5–0 eV, narrowing the band gap, and revealed that a magnetic moment of 2.95 µ B originates from the Cu 3d spin polarization. The combination of experimental and spin-polarized density functional theory offers deep insight into the magnetic characteristics and electronic band structure of copper-substituted SnO 2 quantum dots. The comprehensive experimental and density functional theory analysis demonstrated that unique quantum size effects and long-range ferromagnetism were associated with oxygen vacancy-driven bound magnetic polarons. • Pristine and copper-substituted SnO 2 quantum dots were prepared by the hydrothermal method. • Formation of quantum dot structure was confirmed using X-ray diffraction and Raman studies. • Optical studies indicated the Moss-Burstein effect and band gap exhibited quantum size effects. • Room temperature ferromagnetism with larger coercivity and magnetization was realized. • Spin-polarized DFT reveals a magnetic moment of 2.95 µ B that originates from Cu 3d spin polarization.