Gallium Oxide Research Articles

Regeneration of bulk and silica-supported gallium oxide catalysts applied in the dehydrogenation of methanol to formaldehyde and hydrogen by reaction-oxygen regeneration cycles and oxygen pulses in the feed

The oxygen-free dehydrogenation of methanol to formaldehyde and hydrogen is a potential alternative to the established industrial oxidative dehydrogenation yielding aqueous formaldehyde solutions. Advantages are the production of anhydrous formaldehyde and of hydrogen as a valuable coupled product. However, fast deactivation of the catalyst occurs under the high-temperature reaction conditions mainly due to coking, which can be overcome by applying oxygen at a temperature high enough to allow fast oxidation of the carbon deposits but low enough to prevent the loss of Ga. From an engineering point of view, a stable reaction temperature in the catalyst bed and a high H2 yield have to be maintained, requiring that the catalyst enables methanol dehydrogenation, but not the oxidation of hydrogen to water. Thus, two modes of regeneration of GaOx-based catalysts were investigated using reaction − oxygen regeneration cycles and oxygen pulses in the feed. When using bulk Ga2O3 as catalyst and applying optimized reaction-regeneration cycles, a formaldehyde yield of 51 % and a hydrogen yield of 45 % at a stable methanol conversion of 65 % were achieved, whereas undiluted O2 pulsed into the feed every 30 s resulted in a continuous formaldehyde yield of 40 % and a hydrogen yield of 35 % at a stable methanol conversion of 59 % with water yields below 2 % and 4 %, respectively. The effects of the two operation modes on stability and product distribution are discussed in terms of the carbon removal rate from the surface, refilling of oxygen vacancies and parasitic reactions in the presence of oxygen. Specifically, the consumption of O2 did not lead to excessive water formation but preferentially effected the oxidation of the carbon deposits to CO and CO2.

Replacing the Gallium Oxide Shell with Conductive Ag: Toward a Printable and Recyclable Composite for Highly Stretchable Electronics, Electromagnetic Shielding, and Thermal Interfaces.

Liquid metal (LM)-based composites hold promise for soft electronics due to their high conductivity and fluidic nature. However, the presence of α-Ga2O3 and GaOOH layers around LM droplets impairs conductivity and performance. We tackle this issue by replacing the oxide layer with conductive silver (Ag) using an ultrasonic-assisted galvanic replacement reaction. The Ag-coated nanoparticles form aggregated, porous microparticles that are mixed with styrene-isoprene-styrene (SIS) polymers, resulting in a digitally printable composite with superior electrical conductivity and electromechanical properties compared to conventional fillers. Adding more LM enhances these properties further. The composite achieves EMI shielding effectiveness (SE) exceeding 75 dB in the X-band frequency range, even at 200% strain, meeting stringent military and medical standards. It is applicable in wireless communications and Bluetooth signal blocking and as a thermal interface material (TIM). Additionally, we highlight its recyclability using a biodegradable solvent, underscoring its eco-friendly potential. This composite represents a significant advancement in stretchable electronics and EMI shielding, with implications for wearable and bioelectronic applications.

Physical and enhanced photocatalytic MO dye degradation behaviour of Zn doped β-Ga2O3 microrods

This work explored the effects of Zn doping on the structural, micrographic, optical and photocatalytic behaviour of gallium oxide (β-Ga2O3) microrods. The X-ray diffractogram (XRD) and Raman spectral analyses confirmed the monoclinic structure of β-Ga2O3, with a shift to lower angles in the XRD pattern indicating Zn incorporation into the Ga2O3 lattice. The Scanning electron microscopy (SEM) images revealed a rod-like shape, with the diameter decreasing from 604 nm to 573 nm with Zn doping. Further analysis using TEM, HR-TEM, SAED, EDX, and elemental mapping confirmed the shape, crystallinity, crystal structure, and elemental distribution. The interplanar spacings were measured as 0.4 and 0.2 nm, corresponding to the (002) and (−311) planes of β-Ga2O3. UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) showed a slight shift in the absorption edge, while photoluminescence (PL) analysis demonstrated strong UV and weak visible light emission. Photocatalytic results revealed a high efficiency of dye degradation,(i.e) 98 % (20 ppm) and 89 % (30 ppm) against methyl orange (MO) dye aqueous solution over 150 min, with a rate constant of 0.02/min and 0.01/min, respectively for 1.5 wt% Zn doping. This suggests that the Zn-doped material holds promise as a photocatalyst for wastewater treatment applications.

A strategy for enhancing interfacial thermal transport in Ga2O3-diamond composite structure by introducing an AlN interlayer

Heat dissipation issues have emerged in power devices due to miniaturization and high power density, particularly for materials like low-thermal-conductivity gallium oxide (Ga2O3). Increasing interfacial heat transfer has been identified as a critical strategy for tackling these issues. This study first explored the thermal transport of Ga2O3-diamond interfaces in composite structures containing an AlN interlayer. First-principles calculations revealed that the AlN interlayer improved interfacial bonding between Ga2O3 and diamond. Subsequently, Ga2O3 membranes were deposited on diamond substrates with and without interlayers using pulsed laser deposition (PLD), and the structural and thermal characteristics were examined. The interlayer strategy was shown to be effective in improving the quality of Ga2O3 thin films, including improved crystallinity, a smoother surface, and fewer oxygen vacancies. The thermal characteristics were accordingly improved: the thermal conductivity of Ga2O3 increased from 5.5±0.3–6.0±0.3 W/m·K, and the thermal boundary conductance of Ga2O3-diamond interface (TBCGaO-dia) increased from 46.1±2.3–60.9±3.0 MW/m2·K. Molecular dynamics (MD) analysis further revealed that the enhancement in phonon transmission was due to the increase in the low-frequency phonon participation rate. Additionally, the electro-thermal simulation using COMSOL confirmed the effectiveness of the AlN interlayer in mitigating the self-heating effect. These findings offer a new route for improving interface heat transport and pave the way for the optimization and design of reliable Ga2O3-based devices.

Bubble Printing of Liquid Metal Colloidal Particles for Conductive Patterns.

Bubble printing is a patterning method in which particles are accumulated by the convection of bubbles generated by laser focusing. It is attracting attention as a method that enables the high-speed, high-precision patterning of various micro/nanoparticles. Although the bubble printing method is used for metallic particles and organic particles, most reports have focused on the patterning of solid particles and not on the patterning of liquid particles. In this study, liquid metal wiring patterns were fabricated using a bubble printing method in which eutectic gallium‒indium alloy (EGaIn) colloidal particles (≈diameter 0.7 µm) were fixed on a glass substrate by generating microbubbles through heat generation by focusing a femtosecond laser beam on the EGaIn colloidal particles. The wiring was then made conductive by replacing gallium oxide, which served as a resistance layer on the surface of the EGaIn colloidal particles, with silver via galvanic replacement. Fine continuous lines of liquid metal colloids with a line width of 3.4 µm were drawn by reducing the laser power. Liquid metal wiring with a conductivity of ≈1.5 × 105 S/m was formed on a glass substrate. It was confirmed that the conductivity remained consistent even when the glass substrate was bent to a curvature of 0.02 m-1.

Ultra‐Low BER Encrypted Communication Based on Self‐Powered Bipolar Photoresponse Ultraviolet Photodetector

AbstractUnderwater visible light communication often faces risks such as susceptibility to external light source interference, signal distortion, and information leakage. The cuprous oxide modified gallium oxide nanorod arrays detector prepared in this study can generate bipolar photocurrents under dual‐wavelength ultraviolet light without external bias voltage. Based on it, the constructed self‐powered ultraviolet ASCII code communication system not only reduce power consumption but also significantly enhance anti‐interference capability. Furthermore, the developed solar‐blind ultraviolet AMI and HDB3 ternary code communication systems can realize non‐visible light secure communication and automatic error correction. Notably, the encrypted communication system assembled using the additive property of bipolar photocurrents can also significantly improve communication security and reliability, whose bit error rate is only 0.26‰. This achievement contributes to technical advancements in underwater channel encryption and provides valuable insights for the further application of encrypted communication coding techniques.

Rhodium‐Alloyed Beta Gallium Oxide Materials: New Type Ternary Ultra‐Wide Bandgap Semiconductors

AbstractBeta gallium oxide (β‐Ga2O3) is an ultra‐wide‐bandgap semiconductor with advantages for high‐power electronics. However, the power resistance of β‐Ga2O3‐based devices is still much lower than its material limit due to its flat band dispersion at its valence band maximum (VBM) and the difficulty for p‐type doping. Here, β‐Ga2O3‐based new type ternary ultra‐wide bandgap semiconductors: β‐(RhxGa1‐x)2O3’s alloys are reported with x up to 0.5. The energy and band‐dispersion curvature of β‐Ga2O3’s VBM are significantly enhanced via Rh‐alloying. Compared to that in β‐Ga2O3, the β‐(RhxGa1‐x)2O3’s VBMs increase more than 1.35 eV. The hole mass of β‐(Rh0.25Ga0.75)2O3 is only 52.3% of that in β‐Ga2O3. The decreased hole mass is correlated with the equal Rh─O bond along the b‐axis. Thanks to the simultaneous rise of conduction band minimums, the bandgaps of β‐(RhxGa1‐x)2O3 are still much larger than that in commercial silicon carbide. Moreover, the alloys show direct bandgaps in a wide range of x, and a direct and ultra‐wide bandgap of 4.10 eV is determined in β‐(Rh0.3125Ga0.6875)2O3. Combined with the enhanced valence energy, reduced hole mass, and ultra‐wide bandgap, the β‐(RhxGa1‐x)2O3 can be candidate semiconductors for a new generation of power electronics, ultraviolet optoelectronics, and complementary metal‐oxide‐semiconductor (CMOS) technologies.

Extremely Low Thermal Resistance of β-Ga2O3 MOSFETs by Co-integrated Design of Substrate Engineering and Device Packaging.

Gallium oxide (Ga2O3) emerges as a promising ultrawide bandgap semiconductor, which is expected to surpass the performance of current wide bandgap materials, like GaN and SiC, in electronic devices. However, widespread application of Ga2O3 is hindered by its extremely low thermal conductivity and lack of effective device-level thermal management strategies. In this work, Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated by conducting co-integrated design of substrate engineering with layer transferring and device packaging. 3D Raman thermography is introduced as a novel method to analyze the temperature distribution within the device, which provides valuable insights into their thermal performances. A high-quality Ga2O3-SiC heterogeneous integrated material is successfully fabricated with an extremely low interface thermal resistance of 6.67 ± 2 m2·K/GW. Compared to the homoepitaxial Ga2O3 MOSFETs, the degradation of Ion/Ioff in Ga2O3-SiC MOSFETs is decreased by 1.5 orders of magnitude, and that of Ron is decreased by 31%, showing the great thermal stability of Ga2O3-SiC MOSFETs. With the additional device packaging, a significant one order-of-magnitude reduction in the thermal resistance of the Ga2O3-SiC MOSFET is achieved, reaching a record-low value of 4.45 K·mm/W in the reported Ga2O3 MOSFETs. This work demonstrates an efficient strategy for device-level thermal management in next-generation Ga2O3 power and RF applications.

Internal radiation effect on semiconductor β-Ga2O3 crystals grown by the VB Method and anisotropic thermal stress

Gallium oxide crystals are semitransparent semiconductors with good optical and electrical properties, which allow their use for several technological applications. During the growth process of β-Ga2O3 crystals, internal radiation plays a crucial role that affects the growth process and then the crystal quality. In this work, the effect of the melt and the crystal transparency on the vertical Bridgman growth of β-Ga2O3 oxide is thoroughly studied. Using a global 2D/3D finite element model, temperature, melt flow, melt-crystal interface, and three-dimensional anisotropic thermal stress are computed at different growth stages. At each stage, four cases are considered, namely, opaque melt and crystal, semi-transparent melt and opaque crystal, semitransparent crystal and opaque melt, and finally semitransparent melt and crystal. The role of internal radiation in each case at different growth stages is then highlighted separately and then coupled together. It was found that the melt-crystal interface is shifted from a convex shape at the early stage to a nearly plane and then to a concave shape at the last stage. The melt flow is then changed from two rolls pattern at the beginning to a single-roll structure at the last stage. Thermal stress of the as-grown ingot is decreased during the growth due to the decrease of temperature non-linearities. Internal radiation inside the crystal acts to increase the melt-crystal interface convexity at the early and middle stages of the growth process and leads to a decrease in its concavity at the final stage. However, the melt transparency leads to the opposite effects, i.e., it decreases the interface convexity at the early stage and increases the interface concavity at the final stage. As a result, for semitransparent crystal and melt, the interface is between the two previous cases. The calculated thermal stresses are found to be more affected by the transparency of the crystal than the melt as the absorption coefficient of β-Ga2O3 crystal is smaller than that of the melt. At all stages, the thermal stresses are found to be larger for the opaque case due to the increase of temperature non-linearities in the crystal. Large values are found at the bottom and the lower part of the periphery. Furthermore, internal radiation inside the melt plays a major role during the early growth stage due to the large liquid volume. It reduces the melt flow intensity close to the free surface where the shear stress is combined with the buoyant force and leads to the flattening of the interface decreasing then the radial temperature gradients, which leads to small attenuation of the thermal stress. At the final stage, the transparency of the melt plays the opposite role due to the increase of the interface concavity which leads to an increase in both of the temperature gradients and the thermal stress inside the crystal. Due to the crystal anisotropy, and especially to the large thermal expansion coefficient in the [010] direction, the 3D thermal stress values are found to be larger in this direction, especially in the bottom part of the ingot. Comparisons with available experimental and numerical works are provided in this paper.

High-temperature operation of Al2O3/Ga2O3 bi-layer gate stack GaN MOS-HEMT up to 450 °C with suppressed gate leakage

Abstract In this work, we report the reduced gate leakage current by using aluminum oxide (Al2O3) and gallium oxide (Ga2O3) as a bi-layer gate stack for GaN MOS-HEMT on a silicon substrate up to 450 °C. The bi-layer gate stack MOS-HEMTs suppressed the gate leakage by more than four orders of magnitude compared to only Al2O3-based GaN MOS-HEMT at 450 °C. The low gate leakage current is attributed to the reduced oxygen vacancies present in the Ga2O3 layer, which effectively impede the conduction path of the Poole-Frenkel emission at high temperatures, thereby enhancing the overall performance of GaN HEMTs.

Theoretical investigation of the thermal conductivity of Ga2O3 polymorphs

Gallium oxide (Ga2O3) is a promising thermal preserving and heat-insulating material; understanding the thermal properties is important to improve its performance in technological applications. The thermal conductivities of Ga2O3 polymorphs labeled as α, β, δ, and ε are computed via the Boltzmann phonon transport equation (BTE) employing first-principles techniques. The lattice thermal conductivity tensor k of Ga2O3 for temperatures ranging from 50 K to 1000 K is derived using the second and third-order interatomic force constants (IFCs) for the potential based on a generalized gradient approximation (GGA), as well as the phonon dispersion relation, projected density of states (PDOS), and phonon group velocities. The results agree with the observed experimental values of rhombohedral polymorph β-Ga2O3 and with the previously calculated results of the other phases. At room temperature, the predicted thermal conductivity of the δ-Ga2O3 phase is 15.6 W/(m•K). By breaking down k into mode contributions, it is projected that the optical phonons contribute significantly to the lattice thermal conductivity because of a peculiar phonon dispersion relation.

Unveiling the oxidation stability of 2D gallium-intercalated monolayer epitaxial graphene through correlative microscopy

The oxidation- and air-stability of 2D gallium-intercalated monolayer epitaxial graphene was determined using correlative microscopy. Site-specific studies including AFM, scanning electron microscope, cross section STEM-HAADF, and EELS revealed that the oxygen signal detected by XPS and AES analyses originated from oxidized surface carbon contaminants without the presence of oxygen at the 2D gallium layers. In addition, the air-stability of the 2D gallium was correlated with the presence of intact epitaxial graphene. The absence of graphene leads to oxidation of the 2D gallium in air, consequently losing the crystallinity of the epitaxial gallium layer. This study invokes the importance of correlative microscopy to better understand defects in 2D metals that have been recently recognized through the confinement heteroepitaxy. In addition, this study highlights the advantage of using high spatial resolution STEM techniques in comparison with XPS that has relatively lower resolution.

Flexible Single Microwire X-Ray Detector with Ultrahigh Sensitivity for Portable Radiation Detection System.

Sensitive, flexible, and low false alarm rate X-ray detector is crucial for medical diagnosis, industrial inspection, and scientific research. However, most semiconductors for X-ray detectors are susceptible to interference from ambient light, and their high thickness hinders their application in wearable electronics. Herein, a flexible visible-blind and ultraviolet-blind X-ray detector based on Indium-doped Gallium oxide (Ga2O3:In) single microwire is prepared. Joint experiment-theory characterizations reveal that the Ga2O3:In microwire possess a high crystal quality, large band gap, and satisfactory stability, and reliability. On this basis, an extraordinary sensitivity of 5.9×105µCGyair -1cm-2 and a low detection limit of 67.4nGyairs-1 are achieved based on the prepared Ag/Ga2O3:In/Ag device, which has outstanding operation stability and excellent high temperature stability. Taking advantage of the flexible properties of the single microwire, a portable X-ray detection system is demonstrated that shows the potential to adapt to flexible and lightweight formats. The proposed X-ray detection system enables real-time monitor for X-rays, which can be displayed on the user interface. More importantly, it has excellent resistance to natural light interference, showing a low false alarm rate. This work provides a feasible method for exploring high-performance flexible integrated micro/nano X-ray detection devices.

A Self-Driven Ga2O3 Memristor Synapse for Humanoid Robot Learning.

In recent years, the rapid development of brain-inspired neuromorphic systems has created an imperative demand for artificial photonic synapses that operate with low power consumption. In this study, a self-driven memristor synapse based on gallium oxide (Ga2O3) nanowires is proposed and demonstrated successfully. This memristor synapse is capable of emulating a range of functionalities of biological synapses when exposed to 255nm light stimulation. These functionalities encompass peak time-dependent plasticity, pulse facilitation, and memory learning capabilities. It exhibits an ultrahigh paired-pulse facilitation index of 158, indicating exceptional learning performance. The transition from short-term memory to long-term memory can be attributed to the remarkable relearning capabilities. Furthermore, the potential applications of the memristor synapse is showcased through the successful manipulation of a humanoid intelligent robot. Upon establishing artificial intelligence (AI) systems, the control commands originating from the synaptic device can drive the humanoid robot to perform various actions. Based on the memristor synapses, the autonomous feedback system of the humanoid robot facilitates a good collaboration between robotic actions and bio-inspired light perception. Therefore, this research opens up an effective way to advance the development of neuromorphic computing technologies, AI systems, and intelligent robots that demand ultra-low energy consumption.

Balancing Carrier Dynamics in Oxygen-Vacancy-Tuned Amorphous Ga2O3 Thin-Film Self-Powered Photoelectrochemical-Type Solar-Blind Photodetector Arrays for Underwater Imaging.

Underwater imaging technology plays a pivotal role in marine exploration and reconnaissance, necessitating photodetectors (PDs) with high responsivity, fast response speed, and low preparation costs. This study presents the synergistic optimization of responsivity and response speed in self-powered photoelectrochemical (PEC)-type photodetector arrays based on oxygen-vacancy-tuned amorphous gallium oxide (a-Ga2O3) thin films, specifically designed for solar-blind underwater detection. Utilizing a low-cost one-step sputtering process with controlled oxygen flow, a-Ga2O3 thin films with varying oxygen vacancy (VO) concentrations are fabricated. By balancing the trade-offs among electrocatalytic reactions, charge transfer, carrier recombination, and trapping, both the responsivity and response speed of a-Ga2O3-based self-powered PEC-PDs are simultaneously improved. Consequently, the optimized PEC-PDs demonstrated exceptional performance, achieving a responsivity of 33.75mA W-1 and response times of 12.8ms (rise) and 31.3ms (decay), outperforming the vast majority of similar devices. Furthermore, a pronounced positive correlation between anomalous transient photocurrent spikes and the concentration of VO defects is observed, offering compelling evidence for VO-mediated indirect recombination. Finally, the proof-of-concept solar-blind underwater imaging system, utilizing an array of self-powered PEC-PDs, demonstrated clear imaging capabilities in seawater. This work provides valuable insight into the potential for developing cost-effective, high-performance a-Ga2O3 thin-film-based PEC-PDs for advanced underwater imaging technology.

Comprehensive evaluation of recombination confined performance of CuGaO2 for solar cell application

In the quest to find an outstanding solar energy capturing system that meets requirements like affordability, widespread availability, eco-friendliness, remarkable efficiency, and enduring stability, thorough investigations have been carried out to explore the possibilities presented by ‘Delafossite’ copper gallium oxide (CuGaO2). β-CuGaO2 has an ideal bandgap of 1.5 eV, along with a high absorption coefficient and excellent carrier mobility, making it well-suited for high-efficiency solar cell applications. Theoretical modelling, utilizing the optical and electrical attributes of the CuGaO2 (CGO) material, is employed to analyze its photovoltaic performance when used as an absorber. The detailed balance analysis showed 56.9% of the incident power is wasted in spectrum loss (as thermalisation and non-absorption loss), 10.1% is wasted in intrinsic losses (such as radiative recombination, radiation dilution, entropy generation etc,), extrinsic recombination (originating from electrical losses, parasitic resistance, finite mobility, surface recombination velocity (SRV), non-ohmic contacts etc), eats up another 9.5% and the resultant 23.6% is available as net useful efficiency. Through the careful selection of a suitable buffer counterpart and optimization of material parameters, absorber thickness, defect density, contacts, and SRV, the CGO device dem onstrates an efficiency of 23.6%.

Impedance Spectroscopy Study of Charge Transfer in the Bulk and Across the Interface in Networked SnO2/Ga2O3 Core–Shell Nanobelts in Ambient Air

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO2/Ga2O3 core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO2 core. At temperatures above 530 °C, the thermal reduction of SnO2 and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga2O3 shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO2 nanobelts, as both structures are likely connected through existing SnO2/SnO2 homojunctions comprising thin amorphous layers.

Pulsed X‐Ray Detector Based on Vertical p‐NiO/β‐Ga2O3 Heterojunction Diode

Gallium Oxide (Ga2O3) devices have shown great potential for radiation detection. However, developing Ga2O3 detectors for pulsed radiation monitoring is still challenging, which requires high response sensitivity (R), low noise, high time resolution, and linear outputs. Herein, a vertical p‐NiO/β‐Ga2O3 heterojunction diode (HJD) is fabricated and its performance in X‐ray detection is analyzed. Benefiting from the high quality of the p‐n heterojunction, the HJD exhibits a low‐leakage current density of less than 1.73 × 10−7 A cm−2 at 100 V and features a high R of 7.92 μC Gy−1 cm−2, a low noise equivalent dose rate of 9.14 × 10−12 Gy−1 Hz−0.5 at an X‐ray dose rate of 0.383 Gy s−1, and good linear outputs to X‐ray dose rates from 0.0383 to 1.149 Gy s−1. The conductive process of the HJD detector is dominated by the tunneling mechanism, which leads to a longer response time associated with the trapping and releasing process of the deep‐level traps under the continuous X‐ray illumination. However, the pulsed X‐ray response property shows no significant influence from the slow trapping/releasing process of the traps. As a result, pulsed X‐ray radiation detection with a 50 ns full width is achieved, and the time resolution of the detector is characterized to be 3.31 ns by a 20 ps laser source.

Enhanced hypersensitive (5D0→7F2) transition characteristics of Eu3+ doped β-Ga2O3 microrods

Exploring and realizing the luminescence characteristics of rare earth metal (RE) ions doped gallium oxide (Ga2O3) is crucial for developing optoelectronic device applications. The current research used the solid-state reaction approach to synthesize Ga2O3 microrods doped with various europium (Eu3+) concentrations (0.1, 0.2, 0.3, 0.5, 0.75, and 1 mol). X-ray diffraction (XRD) and Raman spectral analyses confirm the monoclinic structure of β-Ga2O3. The intensity of the Raman phonon modes decreased and a peak shift was observed for Eu:β-Ga2O3. The electron microscopy (SEM, TEM) images depicted a nearly uniform distribution of microrods for undoped and Eu:β-Ga2O3 samples. The interplanar distance (d = 0.290 nm, 0.561 nm, and 0.433 nm), from HR-TEM images, corresponding to (0 0 4), (1 0 0), and (1 0 2) crystallographic orientations confirm the monoclinic structure of β-Ga2O3. The elemental mapping images showed a nearly homogeneous Ga, O, and Eu distribution. The UV–visible diffuse reflectance spectroscopy (UV-DRS) showed a notable reduction in the bandgap as the Eu3+ concentration increased. The emission spectra of Eu: β-Ga2O3 microrods showed a narrow red emission at 612 nm (5D0 → 7F2), which relates to the 5D0 → 7Fj (j = 0, 1, 2, 3) energy level arising from an intra-4f transition of Eu3+ ions upon 394 and 465 nm excitation. The red emission was found to increase with Eu content up to 0.5 mol.%. A quenching of emission due to the multipole–multipole interactions was obtained beyond 0.5 mol.% of Eu. The absolute quantum yield (η) calculated for Eu: β-Ga2O3 (0.5 mol.%) was 3.82 %. The luminescence decay curve using the bi-exponential fit and the average lifetime (τ) of the Eu: β-Ga2O3 (0.5 mol.%) was found to be ∼0.172 ms. CIE chromaticity and correlated color temperature analyses of Eu:β-Ga2O3 microrods yielded a red emission with a superior color purity (93 %). The obtained results suggest that Eu:β-Ga2O3 (0.5 wt.%) microrods could be one of the potential candidates for red light sources.

Multifunctional gallium doped bioactive glasses: a targeted delivery for antineoplastic agents and tissue repair against osteosarcoma

Osteosarcoma (OS) is the mostly commonly occurring primary bone cancer. Despite comprehensive treatment programs including neoadjuvant chemotherapy and tumour resection, survival rates have not improved significantly since the 1970s. Survival rates are dramatically reduced for patients who suffer a local recurrence. Furthermore, primary bone cancer patients are at increased risk of bone fractures. Consequently, there is an urgent need for alternative treatment options. In this paper we report the development of novel gallium doped bioactive glass that selectively kill bone cancer cells whilst simultaneously stimulating new bone growth. Here we show, using a combination of 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide, LIVE/DEAD assays and image analysis, that bioactive glasses containing gallium oxide are highly toxic and reduce both the proliferation and migration of bone cancer cells (Saos-2) in a dose dependant manner. Glasses containing 5 mol% gallium oxide reduced the viability of OS cells by 99% without being cytotoxic to the non-cancerous normal human osteoblasts (NHOst) control cells. Furthermore, Fourier transform infrared and energy-dispersive x-ray spectroscopy results confirmed the formation of an amorphous calcium phosphate/hydroxyapatite like layer on the surface of the bioactive glass particulates, after 7 d incubating in simulated body fluid, indicating the early stages of bone formation. These materials show significant potential for use in bone cancer applications as part of a multimodal treatment.