A review on synthesis and applications of gallium oxide materials

Simulation and experimentation of iron-doped liquid metal-based gallium oxide photocatalysts for environmental applications harnessing solar energy

Gallium-based liquid metals (GLM) have emerged as promising materials for cutting-edge technologies. However, their increased use raises environmental concerns. Sustainable strategies, such as using them as nanophotocatalyst precursors, can help mitigate these impacts. In this work, gallium oxides doped with different atomic ratios of Ga:Fe (100:0, 80:20, 70:30, and 50:50) were synthesized from GLM, characterized, and evaluated in the degradation of an emergent pollutant (acetaminophen). The study considers theoretical modeling through the density functional theory. The photocatalysts were characterized by different techniques to investigate and corroborate the effect of iron on the structural, optical, and morphological properties. The results showed that Fe content influences the properties of gallium oxides. After Fe doping, the band gap of FeGOx decreases to 3.21-2.78 eV. All materials showed photocatalytic activity in the visible region (k 1 = 0.00324 - 0.00562 min- 1 under visible illumination), reaching 65-80% mineralization under visible light, with similar performances under UVA light, making them suitable for use under solar radiation. Among the synthesized materials, FeGO30 displayed the best structural, optical, and morphological properties. Theoretical and experimental results are consistent. Several experiments were conducted using electron, proton, superoxide, and hydroxyl radical scavengers, suggesting that the reaction mechanism of Ac degradation could occur via HO• radicals or oxidation through holes. Additionally, a band diagram is proposed for the FeGOx materials.

Mg-doped α-Ga2O3 Nanorods for the Construction of Photoelectrochemical-Type Self-Powered Solar Blind UV Photodetectors and Underwater Imaging Application

Underwater imaging technologies are increasingly crucial for environmental monitoring and resource exploration. However, the development of advanced photodetectors for such applications faces significant challenges, including interference from ambient visible and infrared light, adaptation to underwater environments, and cost-effectiveness. Photoelectrochemical-type solar-blind photodetectors (PEC-SBPDs) based on wide bandgap semiconductors have shown great promise in overcoming these challenges. Here, a novel approach to enhance the performance of α-Ga2O3-based PEC-SBPDs is presented for underwater imaging through Mg-doping. By employing a low-cost hydrothermal synthesis technique, Mg-doped α-Ga2O3 nanorod arrays are fabricated, which induces the formation of VO-MgGa complexes that enhances the interfacial catalytic activity and improves the transport of photogenerated carriers. The optimized PEC-SBPDs exhibits a remarkable 435% increase in photocurrent response compared to undoped α-Ga2O3, with a peak responsivity of 34.54 mA W-1. A 5 × 5 PEC-SBPD array based on Mg-doped α-Ga2O3 nanorods is successfully demonstrated for underwater solar-blind imaging, achieving clear and efficient imaging in challenging underwater conditions. This study not only highlights the superior performance of Mg-doped α-Ga2O3 in underwater environments but also opens new avenues for the development of high-performance self-powered photodetectors in imaging, sensing, and other related applications.

Effects of Cu, Ag, and Au Elements Doping on the Electronic and Optical Properties of β-Ga2O3 via First-Principles Calculations

β-Ga2O3, as a semiconductor material with an ultrawide band gap (Eg > 4.8 eV), emerges as a promising candidate for ultraviolet (UV)-transparent semiconductors. Its distinctive property of high transparency from visible light to the ultraviolet region gives it broad application prospects in the fields of deep UV light-emitting diodes (LEDs), UV lasers, and electronic devices. This study employed first-principles calculations utilizing the generalized gradient approximation+ U (GGA+U) method to investigate the impact of doping β-Ga2O3 with transition metals including copper (Cu), silver (Ag), and gold (Au) on its electronic structure and optical properties. The findings reveal that under oxygen (O)-rich conditions, the formation energy of the doped system is lower compared to gallium (Ga)-rich conditions. And the Cu-doped β-Ga2O3 is demonstrated to possess the lowest formation energy, indicating an enhanced stability of the β-Ga2O3. Additionally, the intrinsic band gap of β-Ga2O3 is calculated to be 4.853 eV, whereas the band gaps of transition metal (TM)-doped β-Ga2O3 are significantly reduced. Specifically, the band gaps of Cu-doped, Ag-doped, and Au-doped β-Ga2O3 are 1.228, 0.982, and 1.648 eV, respectively. This reduction can be attributed to the introduction of impurity levels by the transition metals, which modify the electron distribution of gallium and oxygen atoms in the vicinity of the Fermi level. Remarkably, β-Ga2O3 exhibits superior ultraviolet light absorption performance, and the incorporation of transition metals such as Cu, Ag, and Au facilitates the expansion of the absorption region from the ultraviolet to the visible light range. This transformation not only enhances the material's light-harvesting capability but also improves the electron transition capability of the intrinsic β-Ga2O3, providing a crucial theoretical foundation for the development of novel β-Ga2O3-based optoelectronic devices.

Synthesis and Upconversion Luminescence Fine-tuning of Yb3+/Ho3+-Doped Indium and Gallium Oxide Nanoparticles

Rare earth (RE) dopants can modulate the bandgap of oxides of indium and gallium and provide extra upconversion luminescence (UCL) abilities. However, relevant UCL fine-tuning strategies and energy mechanisms have been less studied. In this research, InGaO, Ho3+ monodoped and Yb3+/Ho3+ codoped In2O3, and Ho3+ monodoped Yb3Ga5O12 nanoparticles (NPs) were synthesized by a solvothermal method. The effects of Yb3+ and Ho3+ dopants on the crystal structures, UCL properties, and optical bandgaps of the oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UCL spectroscopy, and measurements of decay times, pump power dependence, and transmittance spectra. The crystal structures of oxide products of indium and gallium were significantly modified with RE dopants. In2O3 and Yb3Ga5O12 were selected as the host materials. For Yb3+/Ho3+ codoped In2O3 NPs, there existed energy transfers from the defect states of In2O3 to Ho3+ and from Yb3+ to Ho3+. With a fixed Ho3+ concentration, In2O3:0%Yb3+,2%Ho3+ NPs showed the optimal UCL properties mainly due to In2O3-Ho3+ energy transfer and Ho3+-Yb3+ energy-back-transfer, while with a fixed Yb3+ concentration, In2O3:5%Yb3+,3%Ho3+ NPs with a slight Yb2O3 impurity and Yb3Ga5O12:2%Ho3+ NPs did mainly due to Ho3+-Ho3+ cross-relaxation. Besides, the optical bandgaps of In2O3 and Yb3Ga5O12 were noticeably broadened with RE dopants. These findings can offer feasible directions for the synthesis and UCL fine-tuning of RE-doped oxides of indium and gallium and improve their multifunction application prospects in the fields of semiconductor and UCL nanomaterials.