ZnGa2O4 Research Articles

Cation Occupation Engineering Realizes Valence Modulation of Manganese-Activated ZnGa2O4.

Herein, a series of Mn-activated ZnGa2O4 (ZGO) phosphors have been developed for multifunctional applications. The characteristic green and red emission at 503 and 668 nm of Mn-activated ZGO phosphors can be observed under excitation of 247 and 375 nm, respectively, attributed to the partial oxidation of Mn2+ ions resulting in the coexistence of Mn2+ and Mn4+ ions in the host lattice. The valence modulation of Mn content not only realizes the adjustment of red and green luminescence intensity but also achieves the management of persistent luminescence time and thermo-luminescence time. Further, the codoping of Mg2+ could transform the position occupancy preference of Mn and effectively facilitate the conversion of Mn2+ to Mn4+, leading to the regulation of the valence state of manganese ions. Surprisingly, the existence of Mg2+ ions broadens the emission band of Mn4+ and enhances the photoluminescence intensity to 3.8 times, which can be ascribed to the weakened crystal field leading to the downward shift of the 4T2 energy level and the increase of Mn4+ concentration. For this valence modulation behavior, two different hypotheses about the occupancy of Mg2+ have been proposed to explain the corresponding phenomenon. Finally, the potential applications of the synthesized phosphors have been explored in advanced anticounterfeiting strategies, information storage, and plant lighting field.

Growth optimization, optical, and dielectric properties of heteroepitaxially grown ultrawide-bandgap ZnGa2O4 (111) thin film

Ultrawide bandgap ZnGa2O4 (ZGO) thin films were grown on sapphire (0001) substrates at various growth temperatures with a perspective to investigate the electrical and optical characteristics required for high-power electronic applications. Due to the variation in the vapor pressure of Zn and Ga, severe loss of Zn was observed during pulsed laser deposition, which was solved by using a zinc-rich Zn0.98Ga0.02O target. A pure phase single-crystalline ZGO thin film was obtained at a deposition temperature of 750 °C and an oxygen pressure of 1 × 10−2 Torr. The out-of-plane epitaxial relationship between the sapphire and ZGO thin film was obtained from φ-scan. The x-ray rocking curve of the ZGO thin film grown at 750 °C exhibits a full width at half maximum of ∼0.098°, which indicates a good crystalline phase and quality of the thin film. Core-level x-ray photoelectron spectroscopy of ZGO grown at 750 °C indicated that Zn and Ga were in the 2+ and 3+ oxidation states, respectively, and the atomic ratio of Zn/Ga was estimated to be ∼0.48 from the fitted values of Zn-2p3/2 and Ga-2p3/2. The high-resolution transmission electron microscopy images revealed a sharp interface with the thickness of the ZGO film of ∼265 nm, and the signature of minor secondary phases was observed. The bandgap of the ZGO film at different growth temperatures was calculated from the ultraviolet-diffuse reflectance spectroscopy spectra, and its value was obtained to be ∼5.08 eV for the 750 °C grown sample. The refractive index (n) and the extinction coefficient (k) were determined to be ∼1.94 and 0.023 from the ellipsometric data, respectively, and the real dielectric function (ɛr) was estimated to be ∼6.8 at energy 5 eV. The ultrawide bandgap and dielectric function of ZGO recommend its possible potential applications in deep-ultraviolet optoelectronic devices and high-power electronics.

Formation of quaternary [formula omitted] epilayers driven by thermally induced interdiffusion between spinel [formula omitted] epilayer and [formula omitted] substrate

Zinc aluminogallate, Zn(AlxGa1−x)2O4 (ZAGO), a single-phase spinel structure, offers considerable potential for high-performance electronic devices due to its expansive compositional miscibility range between aluminum (Al) and gallium (Ga). Direct growth of high-quality ZAGO epilayers however remains problematic due to the high volatility of zinc (Zn). This work highlights a novel synthesis process for high-quality epitaxial quaternary ZAGO thin films on sapphire substrates, achieved through thermal annealing of a ZnGa2O4 (ZGO) epilayer on sapphire in an ambient air setting. In-situ annealing x-ray diffraction measurements show that the incorporation of Al in the ZGO epilayer commenced at 850 °C. The Al content (x) in ZAGO epilayer gradually increased up to around 0.45 as the annealing temperature was raised to 1100 °C, which was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy. X-ray rocking curve measurement revealed a small full width at half maximum value of 0.72 °, indicating the crystal quality preservation of the ZAGO epilayer with a high Al content. However, an epitaxial intermediate β–(AlxGa1−x)2O3 layer (β - AGO) was formed between the ZAGO and sapphire substrate. This is believed to be a consequence of the interdiffusion of Al and Ga between the ZGO thin film and sapphire substrate. Using density functional theory, the substitution cost of Ga in sapphire was determined to be about 0.5 eV lower than substitution cost of Al in ZGO. Motivated by this energetically favorable substitution, a formation mechanism of the ZAGO and AGO layers was proposed. Spectroscopic ellipsometry studies revealed an increase in total thickness of the film from 105.07 nm (ZGO) to 147.97 nm (ZAGO/AGO) after annealing to 1100 °C, which were corroborated using TEM. Furthermore, an observed increase in the direct (indirect) optical bandgap from 5.06 eV (4.7 eV) to 5.72 eV (5.45 eV) with an increasing Al content in the ZAGO layer further underpins the formation of a quaternary ZAGO alloy with a tunable composition.

Color tunability and NIR luminescence in Cr3+/Li+ co-doped ZnGa2O4 phosphor for solid state lighting and NIR LEDs

In this work, we report the color tunable photoluminescence in the Cr3+/Li+ doped and co-doped ZnGa2O4 (ZGO) phosphors synthesized by solid state reaction method. The phase and surface morphology of ZGO phosphor were examined by XRD and SEM measurements, respectively. The EDS spectra revealed the presence of Zn, Ga, Cr and O elements in the phosphor. The vibrational structure of the phosphor materials has been analyzed by FTIR measurements. The Cr3+ doped phosphor shows electronic absorption bands at 302, 408 and 544 nm alongwith the host CTB at 260 nm. The optical band gap of the phosphor decreases via doping of Cr3+ and Cr3+/Li+ ions. The ZGO is a self-activated host and emits broad blue emission with maximum at 434 nm upon excitation at 260 nm. The Cr3+ doped phosphors show emission bands due to spin-allowed as well as spin-forbidden transitions due to Cr3+ ion in the blue, green and NIR regions on excitation with 260, 302, 408 and 544 nm wavelengths. The emission intensity is optimum for 0.5 mol% concentration of Cr3+ ion. The emission intensity of Cr3+ doped ZGO phosphor increases via doping of Li+ ion. The color tunability has been observed in the phosphor upon 260 and 302 nm excitations. The lifetimes of 4T2 (4F) and 2E states of Cr3+ ion have been measured and it is found that it decreases with increasing concentrations of Cr3+ and Cr3+/Li+ ions. The Cr3+/Li+ doped and co-doped ZGO phosphors may be suitable candidates for display devices, solid state lighting and NIR LEDs.

H2 O2 -Induced Persistent Luminescence Signal Enhancement Applied to Biosensing.

Persistent luminescence nanoparticles (PLNPs) are innovative materials able to emit light for a long time after the end of their excitation. Thanks to this property, their detection can be separated in time from the excitation, making it possible to obtain images with a high signal-to-noise ratio. This optical property can be of particular interest for the development of in vitro biosensors. Here, wereport the unexpected effect of hydrogen peroxide (H2 O2 ) on the signal intensity of ZnGa2 O4 :Cr3+ (ZGO) nanoparticles. In the presence of H2 O2 , the signal intensity of ZGO can be amplified. This signal amplification can be used to detect and quantify H2 O2 in various media, using non-functionalized ZGO nanoparticles. This small molecule can be produced by several oxidases when they react with their substrate. Indeed, the quantification of glucose, lactic acid, and uric acid is possible. The limit of detection could be lowered by modifying the nanoparticles synthesis route. These optimized nanoparticles can also be used as new biosensor to detect larger molecules such as antigen, using the appropriate antibody. This unique property, i.e., persistent luminescence signal enhancement induced by H2 O2 , represents a new way to detect biomolecules which could lead to a very large number of bioassay applications.

Synthesis and Nanostructure Investigation of Hybrid β-Ga2 O3 /ZnGa2 O4 Nanocomposite Networks with Narrow-Band Green Luminescence and High Initial Electrochemical Capacity.

The material design of functional "aero"-networks offers a facile approach to optical, catalytical, or and electrochemical applications based on multiscale morphologies, high large reactive area, and prominent material diversity. Here in this paper, the synthesis and structural characterization of a hybrid β-Ga2 O3 /ZnGa2 O4 nanocomposite aero-network are presented. The nanocomposite networks are studied on multiscale with respect to their micro- and nanostructure by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and are characterized for their photoluminescent response to UV light excitation and their electrochemical performance with Li-ion conversion reaction. The structural investigations reveal the simultaneous transformation of the precursor aero-GaN(ZnO) network into hollow architectures composed of β-Ga2 O3 and ZnGa2 O4 nanocrystals with a phase ratio of ≈1:2. The photoluminescence of hybrid aero-β-Ga2 O3 /ZnGa2 O4 nanocomposite networks demonstrates narrow band (λem = 504nm) green light emission of ZnGa2 O4 under UV light excitation (λex = 300nm). The evaluation of the metal-oxide network performance for electrochemical application for Li-ion batteries shows high initial capacities of ≈714 mAh g-1 at 100mA g-1 paired with exceptional rate performance even at high current densities of 4 A g-1 with 347 mAh g-1 . This study provides is an exciting showcase example of novel networked materials and demonstrates the opportunities of tailored micro-/nanostructures for diverse applications a diversity of possible applications.

Effect of Annealing Time on Structural and Optical Properties of ZnGa2O4: Cr3+ (2.0mol %) Nanostructure Prepared by Sol Gel Method

ZnGa2 O4 : Cr3+ (2.0mol %) nanopowders annealed at annealing times (AT) of = 1, 2, 3, and 4H (hour) were synthesized by the sol-gel method. X-ray diffraction (XRD) results confirmed that the prepared ZnGa2 O4 : Cr3+ samples were cubic structures. In this study we showed that the annealing time has no pronounced influence on the ZnGa2O4: Cr3+ crystallite size at annealing times in the range of 1H to 3H. A significant change in the crystallite size was observed for the sample annealed for a relatively long time (4H). Scanning electron microscopy (SEM) images show the morphology of the prepared nanopowders influenced by annealing time. UV-visible spectrophotometer measurements showed that the energy gap of the prepared nanoparticles could be tuned from 4.50 to 4.12 eV as the annealing time changed from 1H to 4H. Photoluminescence (PL) measurement showed that the annealing time increased, and the PL intensity also increased reaching the maximum value for the sample annealed at AT=3H. Energy dispersive X-ray spectroscopy (EDS) measurements confirmed the presence of Zn, Ga, O and Cr ions.

Structure Effect on the Response of ZnGa2O4 Gas Sensor for Nitric Oxide Applications.

We fabricated a gas sensor with a wide-bandgap ZnGa2O4 (ZGO) epilayer grown on a sapphire substrate by metalorganic chemical vapor deposition. The ZGO presented (111), (222) and (333) phases demonstrated by an X-ray diffraction system. The related material characteristics were also measured by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. This ZGO gas sensor was used to detect nitric oxide (NO) in the parts-per-billion range. In this study, the structure effect on the response of the NO gas sensor was studied by altering the sensor dimensions. Two approaches were adopted to prove the dimension effect on the sensing mechanism. In the first approach, the sensing area of the sensors was kept constant while both channel length (L) and width (W) were varied with designed dimensions (L × W) of 60 × 200, 80 × 150, and 120 ×100 μm2. In the second, the dimensions of the sensing area were altered (60, 40, and 20 μm) with W kept constant. The performance of the sensors was studied with varying gas concentrations in the range of 500 ppb~10 ppm. The sensor with dimensions of 20 × 200 μm2 exhibited a high response of 11.647 in 10 ppm, and 1.05 in 10 ppb for NO gas. The sensor with a longer width and shorter channel length exhibited the best response. The sensing mechanism was provided to explain the above phenomena. Furthermore, the reaction between NO and the sensor surface was simulated by O exposure of the ZGO surface in air and calculated by first principles.

Mechanoluminescence from highly transparent ZGO:Cr spinel glass ceramics

Light emission in response to mechanical stimulation-termed mechanoluminescence (ML)-enables the optical detection and visualization of mechanical strain. In particular, materials with ML response in the transmission window of aqueous media or biological tissue enable in situ stress level monitoring, biophysical imaging or mechanically induced light delivery. However, most of today’s ML materials are polycrystalline ceramics or ceramic particle composites, which puts constraints on their bulk processability, material homogeneity and optical transparency. Here, we demonstrate ML from highly transparent glass ceramics comprising of a high-volume fraction of extraordinarily small Cr3+-doped ZnGa2O4 (ZGO) crystals embedded in a binary potassium germanate glass matrix. The ZGO phase is precipitated directly from the precursor glass by homogeneous nucleation in a narrow temperature window; entropic phase separation and a self-limited crystal growth rate yield a crystal number density above 1023 m-3. The residual glass matrix encapsulates these crystals in a dense, highly homogeneous material, whereby the microstructural stability and the extended supercooling range of the glass enable glass-like processing, for example, in the shapes of fiber, beads or microspheres.

Influence of Al doping on crystal structure, optical, and photoluminescence characteristics of ZnGa2O4 films

Al-doped ZnGa2O4 (ZAGO) thin film phosphors were grown on the c-plane sapphire substrates by co-sputtering of ceramic ZnGa2O4 (ZGO) and metallic Al targets with the Al concentration in the range of 0–5.35%. A systematic investigation on the effects of Al dopant contents on the crystal structure and optical characteristics of ZAGO films has been conducted. First principle calculations were performed to investigate the preferable site of Al atoms in ZAGO supercell in detail. The high-crystalline nature of 1.65% ZAGO film was evidenced by X-ray diffraction patterns and transmission electron microscopy. Al doping revealed the enhanced bandgap of 5.32 eV for ZAGO films. The X-ray photoelectron spectroscopy was utilized in order to determine the chemical states as well as the stoichiometric Zn/Ga ratio in the ZAGO films. The crystallinity, optical, and photoluminescence (PL) characteristics of the ZAGO films are found strongly influenced by Al doping, O/(Zn + Ga + Al), and Zn/Ga ratio. The PL spectra exhibited the broad bands expanding from 380 to 600 nm with the peak located at 525 nm. The improved PL characteristics of ZAGO phosphors with trace Al (1.65%) demonstrate the promise of a relatively new semiconductor material system ZAGO for high-crystalline thin film phosphors.

CO2 reduction by photocatalytic and photoelectrocatalytic approaches over Eu(III)-ZnGa2O4 nanoparticles and Eu(III)-ZnGa2O4/ZnO nanorods

Value-added products by CO2 reduction have extensively been researched using many developed catalysts. Herein, Eu(III)-doped ZnGa2O4 (ZGO) nanoparticles and ZGO hybridized ZnO nanorods (ZGO/ZnONR) were evaluated for photocatalytic and photoelectrocatalytic CO2 reduction under diverse experimental conditions. For photocatalytic CO2 reduction, the CO/CH3OH production ratio was > 1 for ZGO, but < 1 for ZGO/ZnONR. For electrochemical CO2 reduction, CO and H2 were major products with minor formate, and dependent on the parameters including Eu(III)-doping. H2 and formate were increased with increasing applied potential, and CO showed the highest Faradaic efficiency at −1.6 V (vs. Ag/AgCl). Syngas (H2/CO) ratio was shown to be efficiently controlled from 0.5 to 2.0. UV light showed a dramatic effect on increasing CO production but not on H2. Formate was also increased under UV light. Overall, the present study provides strategies of controlling reduction products and syngas ratio by employing hybridized ZGO/ZnONR, doping, and UV light.

Effect of dopant concentration on the optical characteristics of Cr3+:ZnGa2O4 transparent ceramics exhibiting persistent luminescence

ZnGa2O4 (ZGO) persistent luminescence (PersL) ceramics doped with different concentrations of Cr3+ were prepared by the co-precipitation method and hot isostatic pressing (HIP) post-treatment. After HIP post-treatment, the ZGO PersL ceramics was significantly improved from opaque to transparent visual appearance due to the elimination of micro-pores during HIP process. The effects of Cr3+ concentration on the morphology, transmittance and PersL properties of ZGO PersL ceramics were systematically investigated. The ZGO PersL ceramics with higher Cr3+ dopant concentrations show less micro-pores and higher transmittance, which indicates that the Cr3+ can also work as a sintering additive to increase the density and to improve the optical quality of ZGO PersL ceramics. The photoluminescence excitation (PLE) and emission (PL) intensities increase with the increase of Cr3+ concentration up to 0.25 at.%. At yet higher Cr3+ concentrations, the ZGO PersL ceramics exhibits weaker PL and PLE intensities which is probably caused by the concentration quenching effect. However, the PersL decay curves show that the PersL performance of ZGO ceramics increases with increasing Cr3+ concentrations, indicating that the doping by Cr3+ ions may cause another traps formation leading to stronger and longer PersL. The PersL decay curves of all ZGO PersL ceramics were fitted by the second-order exponential function, indicating that at least two kinds of traps with different electron release rates exist in the ZGO ceramics. The influence of Cr3+ concentration on the thermoluminescence (TL) of ZGO PersL ceramics was also studied, and the results showed that the TL curves of the pre-sintered ceramics shifted to lower temperatures, indicating that the depth of trap related to Cr3+ ions is shallower than the depth of trap caused by the intrinsic defects.

Growth and characterization of co-sputtered Al-doped ZnGa2O4 films for enhancing deep-ultraviolet photoresponse

Al-doped ZnGa2O4 (ZGO) films were deposited on c-plane sapphire substrates by co-sputtering of Al and ZGO targets at a substrate temperature of 400 ℃ and thermally annealed at 800 ℃ to enhance their crystalline quality. In this investigation, the DC power for metallic Al target was varied from 0 to 50 W and its effect on structural, optical, and optoelectronic properties of these films were investigated. After annealing, all films exhibited the crystalline nature with the ZGO phase. Further, this investigation revealed that the 800 ℃ annealed Al-doped ZGO film deposited with the 20 W DC power possessed the highest crystalline quality among other films along with the wide-bandgap of 5.18 eV. The X-ray photoemission spectrum measurements revealed from the Ga 2p3/2 and Al 2p core-level spectra that the Al atoms occupy the octahedral sites, which makes Al─O─Ga bonding in the ZGO network. The metal–semiconductor-metal photodetector with this annealed 20 W Al-doped ZGO film exhibited the photocurrent to the dark current ratio of 3.35 × 104 and high responsivity of 3.01 A/W (at 3 V and 220 nm), which shows the enhancement in device performance about 12 times when compared with that of annealed 0 W Al-doped ZGO photodetector.

On the relation of structural disorder and thermoelastic properties in ZnGa2O4 and Zn1−xMgxGa2O4 (x ≈ 0.33)

The cation distribution at room temperature, as well as elastic properties and thermal expansion of single crystal ZnGa2O4 (ZGO) and Zn1−xMgxGa2O4 (x ≈ 0.33; ZMGO) with spinel-type structure were studied in a wide temperature range using single crystal X-ray diffraction, neutron powder diffraction, inductive gauge dilatometry and resonant ultrasound spectroscopy. ZGO adopts an almost normal spinel structure, whereas ZMGO is significantly disordered. At room temperature, the elastic properties of ZMGO mostly fall between those of ZGO and MgGa2O4 (MGO). The temperature dependences of the thermoelastic properties of ZGO and ZMGO, as well as thermal expansion of ZGO reveal distinct signatures of glass-like transitions, which separate states in which the cation dynamics are fast enough to relax the cation order in response to temperature change in laboratory timescales from those in which they are not. In equilibrium, thermal expansion is increased in ZMGO, whereas the thermoelastic coefficients are decreased in both ZGO and ZMGO. The temperature range of the transition is significantly larger in ZGO compared to ZMGO and MGO. Trends within the elastic properties, thermoelastic properties, thermal expansion and the glass-like transition in the (Zn,Mg)Ga2O4 solid solution series are discussed based on the impact of inversion, structural disorder, bond character and in comparison to other spinels.

Molten-Salt-Assisted Annealing for Making Colloidal ZnGa2 O4 :Cr Nanocrystals with High Persistent Luminescence.

Persistent luminescent nanocrystals (PLNCs) in the sub-10 nm domain are considered to be the most fascinating inventions in lighting technology owing to their excellent performance in anti-counterfeiting, luminous paints, bioimaging, security applications, etc. Further improvement of persistent luminescence (PersL) intensity and lifetime is needed to achieve the desired success of PLNCs while keeping the uniform sub-10 nm size. In this work, the concept of molten salt confinement to thermally anneal as-synthesized ZnGa2 O4 :Cr3+ (ZGOC) colloidal NCs (CNCs) in a molten salt medium at 650 °C is introduced. This method led to significantly monodispersed and few agglomerated NCs with a much improved photoluminescence (PL) and PersL intensity without much growth in the size of the pristine CNCs. Other strategies such as i) thermal annealing, ii) overcoating, and iii) the core-shell strategy have also been tried to improve PL and PersL but did not improve them simultaneously. Moreover, directly annealing the CNCs in air without the assistance of molten salt could significantly improve both PL and PersL but led to particle heterogeneity and aggregation, which are highly unsuitable for in vivo imaging. We believe this work provides a novel strategy to design PLNCs with high PL intensity and long PersL duration without losing their nanostructural characteristics, water dispersibility and biocompatibility.

Neutrophil Delivered Hollow Titania Covered Persistent Luminescent Nanosensitizer for Ultrosound Augmented Chemo/Immuno Glioblastoma Therapy.

Glioblastoma (GBM) is the most malignant brain tumor with unmet therapeutic demand. The blood‐brain‐barrier (BBB) and tumor heterogeneity limit the treatment effectiveness of various interventions. Here, an ultrasound augmented chemo/immuno therapy for GBM using a neutrophil‐delivered nanosensitizer, is developed. The sensitizer is composed of a ZnGa2O4:Cr3+ (ZGO) core for persistent luminescence imaging and a hollow sono‐sensitive TiO2 shell to generate reactive oxygen species (ROS) for controlled drug release. Immune checkpoint inhibitor (Anti‐PD‐1 antibody) is trapped in the interior of the porous ZGO@TiO2 with paclitaxel (PTX) loaded liposome encapsulation to form ZGO@TiO2@ALP. Delivered by neutrophils (NEs), ZGO@TiO2@ALP‐NEs can penetrate through BBB for GBM accumulation. After intravenous injection, ultrasound irradiation at GBM sites initiates ROS generation from ZGO@TiO2@ALP, leading to liposome destruction for PTX and anti‐PD‐1 antibody release to kill tumors and induce local inflammation, which in‐turn attractes more ZGO@TiO2@ALP‐NEs to migrate into tumor sites for augmented and sustained therapy. The treatment enhances the survival rate of the GBM bearing mice from 0% to 40% and endows them with long‐term immuno‐surveillance for tumor recurrence, providing a new approach for precision therapy against GBM and other cancers.

Near‐Infrared Nanophosphor Embedded in Mesoporous Silica Nanoparticle with High Light‐Harvesting Efficiency for Dual Photosystem Enhancement

Light-harvesting and conversion ability is important to promote plant growth, and especially when resources are limited. A near-infrared (NIR) nanophosphor embedded with mesoporous silica nanoparticles (MSN), ZnGa2 O4 :Cr3+ ,Sn4+ (ZGOCS), was developed and its optical properties were harnessed to enhance the photosynthetic ability of Brassica rapa spp. chinensis. The broad excitation of ZGOCS from the ultraviolet to the visible region allowed the conversion of extra light into near-infrared light (650-800 nm) and thus promoted the dual photosystem via the Emerson effect. ZGOCS@MSN was spherical with a size of 65±10 nm and good dispersion. A light conversion ability of up to 75 % under different wavelengths was achieved. Moreover, the electron transfer rate of photosynthesis increased by 100 % with a suitable ZGOCS@MSN concentration. Plant and animal models were used to explore the effects of the nanophosphor. ZGOCS@MSN distribution was tracked by monitoring its NIR emission in plant and animal tissues, demonstrating that this nanophosphor can be potentially utilized in plant growth.

Radioiodinated Persistent Luminescence Nanoplatform for Radiation-Induced Photodynamic Therapy and Radiotherapy.

Radionuclide with Cerenkov radiation (CR) can serve as an internal excitation source to activate photosensitizers for photodynamic therapy (PDT) in deep tumor. However, the low efficiency of CR limits its therapeutic efficacy. A 131 I labeled zinc tetra(4-carboxyphenoxy) phthalocyaninate (ZnPcC4) conjugated Cr3+ -doped zinc gallate (ZnGa2 O4 :Cr3+ , ZGCs) nanoplatform (131 I-ZGCs-ZnPcC4) is developed for radiotherapy (RT) and radiation-induced PDT. 131 I can not only activate ZGCs for long-lasting luminescence via both Cerenkov luminescence (CL) and ionizing radiation, which further continuously activate photosensitizer ZnPcC4 for PDT, but also can directly kill cancerous cells. This 131 I-ZGCs-ZnPcC4 exhibits excellent tumor inhibition both in vitro and in vivo. Combining self-activated PDT and RT, it is believed that the 131 I-ZGCs-ZnPcC4 can greatly benefit the deep tumor therapy.

In Vivo Repeatedly Activated Persistent Luminescence Nanoparticles by Radiopharmaceuticals for Long-Lasting Tumor Optical Imaging.

Persistent luminescence nanoparticles (PLNPs) with rechargeable near-infrared afterglow properties attract much attention for tumor diagnosis in living animals since they can avoid tissue autofluorescence and greatly improve the signal-to-background ratio. Using UV, visible light, or X-ray as excitation sources to power up persistent luminescence (PL) faces the challenges such as limited tissue penetration, inefficient charging capability, or tissue damage caused by irradiation. Here, it is proved that radiopharmaceuticals can efficiently excite ZnGa2 O4 :Cr3+ nanoparticles (ZGCs) for both fluorescence and afterglow luminescence via Cerenkov resonance energy transfer as well as ionizing radiation. 18 F-FDG, a clinically approved tumor-imaging radiopharmaceutical with a short decay half-life around 110 min, is successfully used as the internal light source to in vivo excite intravenously injected ZGCs for tumor luminescence imaging over 3 h. The luminescence with similar decay time can be re-obtained for multiple times upon injection of 18 F-FDG at any time needed with no health concern. It is believed this strategy can not only provide tumor luminescence imaging with high sensitivity, high contrast, and long decay time at desired time, but also guarantee the patients much less radiation exposure, greatly benefiting image-guided surgery in the future.

Thin film transistors based on ultra-wide bandgap spinel ZnGa2O4

We report on thin film transistors (TFTs) based on spinel ZnGa2O4 (ZGO) that was recently spotlighted as an ultra-wide bandgap oxide semiconductor. The ZGO layers were grown in a spinel structure by pulsed laser deposition on the cubic spinel MgAl2O4 (MAO) as well as on cubic MgO substrates while changing the Zn/Ga ratio. The compressive strained epitaxial growth of ZGO on MgAl2O4 (100) and the tensile strained epitaxial growth of ZGO on MgO (100) without any misfit or threading dislocations were confirmed by the reciprocal space map and cross-sectional transmission electron microscopy. The electrical transport properties were demonstrated through TFTs based on ZGO as the channel layer, Al2O3 as the gate oxide, and Sn-doped In2O3 as the source, drain, and gate electrodes. When the Zn/Ga ratio is slightly lower than the ideal value of 0.5 on MgO substrates, the ZGO TFT showed the highest mobility of 5.4 cm2/V s. The ION/IOFF ratio and subthreshold swing (S) value are 4.5 × 108 and 0.19 V/dec, respectively.