α-Ag_2-2xZn_xWO₄ (0 ≤ x ≤ 0.25) Solid Solutions: Structure, Morphology, and Optical Properties

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Silver tungstate (α-Ag₂WO₄) is a material with interesting optical and electronic properties.
• Doping with other elements can tune these properties for specific applications.
• Understanding the structural and electronic modifications induced by doping is crucial for material design.

Purpose of the Study:

• To investigate the effects of zinc (Zn²⁺) doping on the structural, morphological, and electronic properties of α-Ag₂WO₄.
• To support experimental findings with theoretical calculations based on density functional theory (DFT).
• To elucidate the relationship between doping-induced changes and photoluminescence properties.

Main Methods:

• Synthesis of Zn-doped α-Ag_2-2xZn_xWO₄ (0 ≤ x ≤ 0.25) solid solutions via coprecipitation.
• Characterization using X-ray diffraction (XRD) and micro-Raman spectroscopy.
• Theoretical calculations employing DFT with the B3LYP hybrid functional for band structure and surface energy analysis, alongside Wulff constructions.

Main Results:

• Zn-doping resulted in α-Ag_2-2xZn_xWO₄ with an orthorhombic structure, reduced crystal size, and altered morphology (rod-like to roll-like).
• A decrease in band gap from 3.18 to 3.08 eV and a red shift in photoluminescence were observed with increasing Zn²⁺ content.
• DFT calculations confirmed an indirect band gap and revealed that electronic properties and photoluminescence shifts are influenced by lattice distortions and oxygen vacancies (V_O^x).

Conclusions:

• The substitution of Ag⁺ by Zn²⁺ in α-Ag₂WO₄ leads to significant structural, morphological, and electronic property modifications.
• Theoretical and experimental results consistently explain the observed changes in band gap and photoluminescence due to doping-induced effects.
• The study provides insights into the random substitution of Zn²⁺ in the α-Ag₂WO₄ lattice, favoring the Ag4 site.