Effect of rare earth ions on the optical and electronic properties of defect chalcopyrite: Experimental and theoretical investigation

The present research is a systematic experimental and computational study focused on structural, electronic, and optical properties of ZnGa₂S₄ doped with neodymium rare earth ions for the first time. High-intensity, narrow-band luminescence peaks are observed in the visible and infrared regions by doping the matrix with Nd ions. These peaks in the background of the broadband spectrum are due to intercenter 4f-4f transitions of Nd³⁺ ions. The fact that the Raman peaks of the alloy crystal are more intense than that of the pure crystal confirms that the neodymium does not move freely in the lattice and occupies the place of defects. This confirms the results from our X-ray structural analysis. The crystal lattice parameters of the studied materials were determined as follows: a = 5.496 Å, c = 10.99 Å, c/a = 2. To explain the electronic, optical and magnetic properties, using ATK-DFT method, electronic energy band structure, density of states and optical spectrum for pure and doped with ZnGa₂S₄:Nd compound are computed and discussed. DFT result shows that impurity Nd leads to a decreased bandgap of ZnGa₂S₄ due to the hybridization of Nd-4d with S-3p orbital in the forbidden gap. The peaks in the optical spectrum are shifted toward the lower energy range for doped supercell.