Effect Of Doping On Magnetic/Optical Properties And Electronic Structure Of In₂S₃

By combining the spin and charge degrees of freedom of electrons,spintronics devices exhibit many advantages,such as high speeds,high storage density,small volume,low-power-consumption and non-volatile memory,which make them possess the prospect applying very broadly in electronic information science and technology.Diluted magnetic semiconductors as the most potential material for spintronics devices,have become the hotspot of science community.The preparation of novel materials with optical,electrical and magnetic properties will open the way to new generation of multi-functional spintronic devices.In₂S₃ has many vacancy defects due to its defective spinel structure,which facilitates the incorporation of guest ions.In₂S₃,having low toxicity,stable physicochemical characteristics,and excellent optical and electrical properties,has been applied widely in photocatalysis,solar cells,spin-dependent optoelectronic devices and other multi-functional devices.Doping,as an effective method to change the properties of semiconductor materials,can tune the optical,electrical and magnetic properties of materials by regulating dopant concentration.In this work,the doped In₂S₃ nanoparticles with rare earth elements?Gd,Tm and Sm?and transition metal?Cu?were fabricated and showed luminescence,photoelectric properties and room temperature ferromagnetism.The effect of doping concentration on the optical and magnetic properties of the as-obtained samples were studied experimentally.The electronic structure and magnetic origin of the samples were systematically analyzed by the first-principles calculations.The main results obtained in this paper are as follows:1.The undoped In₂S₃ and In₂S₃:Gd nanoparticles of about 3-5 nm in size with tetragonal phase were fabricated by gas-liquid phase chemical deposition method.The UV-vis absorption spectra show that the as-synthesized samples have strong absorption in the visible light region,and the bandgap values of the samples first increase and then decrease with increasing Gd dopant content.The particle sizes of the samples are smaller than the exciton Bohr radius of In₂S₃?33.8 nm?,therefore,the photoluminescence?PL?spectra show a significant blue shift due to strong quantum confinement effect.The magnetic measurement results show that all samples exhibit room temperature ferromagnetism,and the saturation magnetizations of the samples increase as Gd content increased and then gradually decreased.This phenomenon can be reasonably explained based on bound magnetic polarons mechanism.The first principle calculation reveal that the ferromagnetism of the system is induced by In vacancies and Gd dopants,and the total magnetic moment is mainly contributed by S3p states around the In vacancy and Gd 4f states.2.In₂S₃:Tm nanoparticles?3-5 nm?with different doping concentration were synthesized.Doped rare earth element Tm results in redshift of optical absorption edge and reduction of bandgap values.The UV-vis absorption spectra show that absorption bands at 686 nm and 789 nm are ascribed to ³H₆?³H_2,3 and ³H₆?³H₄transitions of Tm³⁺ions.The low Tm doping concentrations lead to the increased PL intensities of the samples.For Tm doping concentration higher than 1.22 at.%,the PL intensities are gradually decreased because of the concentration quenching.Analyses on the concentration quenching reveal that electric dipole-dipole interaction is the main physical mechanism.The fluorescence lifetimes of the samples decrease with the increase Tm dopant concentration,indicating that the effective energy transfer occur between the host In₂S₃ and the doped Tm³⁺ions.The photoelectric properties were investigated by manufacturing p-si/In₂S₃ heterostructures and the measured results reveal that the introduction of Tm³⁺ions significantly improve the sensitivity of In₂S₃ to visible light.In addition,the In₂S₃:Tm nanoparticles display room temperature ferromagnetism,and the values of the saturation magnetizations can be regulated by changing the Tm³⁺dopant concentration.The density-of-states calculations show that incorporation of the Tm³⁺ions decrease bandgap values of host In₂S₃ and increase carrier concentration,and the ferromagnetism of the In₂S₃:Tm samples mainly originates from the Tm 4f orbitals.3.The undoped In₂S₃ and In₂S₃:Sm nanoparticles?around 3-5 nm?with high purity were fabricated.The bandgap values of the system can be tuned by regulating Sm³⁺dopant concentration.The introduction of Sm³⁺ions results in PL intensities enhanced due to increased internal defects and decreased the local symmetry.The all samples exhibit room temperature ferromagnetism,and the values of the saturation magnetizations increase first and then decrease with the increase of Sm dopant concentration.The weak ferromagnetism signal in undoped In₂S₃ nanoparticles is induced by vacancy defects formed during crystal growth,and the first principle calculation confirm that the magnetism of In₂S₃ is due to In vacancy.The ferromagnetism of the defect complex system with In vacancy and Sm doping is derived from the nearest neighboring S 3p states around the In vacancy and Sm 4f states.The calculated band structures results show that the as-synthesized samples is characteristic of the indirect band-to-band transition,and the doped Sm³⁺ions lead to bandgap narrowing,which are consistent with the measured result of UV-vis diffuse reflectance spectra.4.The pristine In₂S₃ and In₂S₃:Cu nanoparticles with room temperature ferromagnetism were prepared.The absorption edge position of the as-synthesized samples can be manipulated by changing the Cu doping concentration.The introduction of Cu leads to the increase of defect states in host In₂S₃,resulting in enhanced PL intensities.The saturation magnetizations of the samples increase monotonously with the increase of Cu dopant concentration,indicating that Cu doping can enhance the ferromagnetism of In₂S₃.The first principle calculations show that In vacancies play an important role in inducing ferromagnetism.The spin polarization of the Cu doped system arises from the orbitals hybridization between S 3p states and Cu3d states.The contribution of magnetic moment mainly comes from S 3p states surrounding indium vacancy and Cu 3d states.