ZnGa2O4 Research Articles

Low Dose of X-Ray-Excited Long-Lasting Luminescent Concave Nanocubes in Highly Passive Targeting Deep-Seated Hepatic Tumors.

Chromium-doped zinc gallate, ZnGa2 O4 :Cr3+ (ZGC), is viewed as a long-lasting luminescence (LLL) phosphor that can avoid tissue autofluorescence interference for in vivo imaging detection. ZGC is a cubic spinel structure, a typical agglomerative or clustered morphology lacking a defined cubic shape, but a sphere-like feature is commonly obtained for the nanometric ZGC. The substantial challenge remains achieving a well-defined cubic feature in nanoscale. The process by which dispersed and well-defined concave cubic ZGC is obtained is described, exhibiting much stronger LLL in UV and X-ray excitation for the dispersed cubic ZGC compared with the agglomerative form that cannot be excited using X-rays with a low dose of 0.5 Gy. The cubic ZGC reveals a specific accumulation in liver and 0.5 Gy used at the end of X-ray excitation is sufficient for imaging of deep-seated hepatic tumors. The ZGC nanocubes show highly passive targeting of orthotopic hepatic tumors.

NO gas sensor based on ZnGa2O4 epilayer grown by metalorganic chemical vapor deposition

A gas sensor based on a ZnGa2O4(ZGO) thin film grown by metalorganic chemical vapor deposition operated under the different temperature from 25 °C to 300 °C is investigated in this study. This sensor shows great sensing properties at 300 °C. The sensitivity of this sensor is 22.21 as exposed to 6.25 ppm of NO and its response time is 57 s. Besides that, the sensitivities are 1.18, 1.27, 1.06, and 1.00 when exposed to NO2(500 ppb), SO2 (125 ppm), CO (125 ppm), and CO2 (1500 ppm), respectively. These results imply that the ZGO gas sensor not only has high sensitivity, but also has great selectivity for NO gas. Moreover, the obtained results suggest that ZGO sensors are suitable for the internet of things(IOT) applications.

Broadband Cr3+ , Sn4+ -Doped Oxide Nanophosphors for Infrared Mini Light-Emitting Diodes.

Light-emitting diodes break barriers of size and performance for displays. With devices becoming smaller, the materials also need to get smaller. Chromium(III)-doped oxide phosphors, which emit near-infrared (NIR) light, have recently been used in small electronic devices. In this work, mesoporous silica nanoparticles were used as nanocarriers. The nanophosphor ZnGa2 O4 :Cr3+ ,Sn4+ formed in the mesopore after sintering. Good dispersity and morphology were performed with average diameters of 71±7 nm. It emitted light at 600-850 nm; the intensity was optimized by tuning the doping ratio of Cr3+ and Sn4+ . Meanwhile, the light conversion efficiency increased from 7.8 % to 37 % and the molar concentration increased from 0.125 m to 0.5 m. The higher radiant flux of 3.3 mW was obtained by operating an input current of 45 mA. However, the NIR nanophosphor showed good performance on mini light-emitting diode chips.

Controlling the white phosphorescence ZnGa2O4 phosphors by surface defects

White phosphorescence that lasted ≈ 212 s, being the longest phosphorescence time reported so far for any Ga based material, has been observed in undoped ZnGa2O4 (ZGO) phosphors. The samples were synthesized by a simple combustion method by using two different Gallium precursors (Gallium nitrate and Gallium Acetylacetonate). According to the X-ray diffraction analysis, the samples prepared with the two different precursors presented the same single cubic phase. TEM images demonstrated that the ZGO phosphors made with both precursors are formed by nanoparticles with quasi-spherical shape, and they have nanoparticle sizes in the range of 17–43 nm. When excited with UV light (400 nm), these phosphors produced a broad blue-green-yellow luminescence. The blue band was associated to transitions from the Ga-O levels, while that of green-yellow band was attributed to radiative transitions from oxygen vacancies. Particularly, the sample synthesized with Gallium acetylacetone precursor presented the highest phosphorescent emission intensity and had a CIE coordinates of (x = 0.27, y = 0.33), which is close to that for pure white light (x = 0.33, y = 0.33). Since the ZGO presented a white phosphorescent emission without doping with rare earths, they could be good candidates for lighting or signaling applications.

Oxygen Vacancy-Modified B-/N-Codoped ZnGa2O4 Nanospheres with Enhanced Photocatalytic Hydrogen Evolution Performance in the Absence of a Pt Cocatalyst

Here, we report oxygen vacancy (VO)-modified B/N-codoped ZnGa2O4 (VO-B/N-ZGO) nanospheres, showing excellent photocatalytic H2 production even without a Pt cocatalyst, which is better than that obtained with VO-modified B-doped ZnGa2O4 (VO-B-ZGO) or N-doped ZnGa2O4 (N-ZGO) and as high as about three times of that achieved with the undoped ZnGa2O4 (ZGO) photocatalyst. The dramatically enhanced photocatalytic activity of VO-B/N-ZGO predominately originates from the improvement of charge separation and surface activation. Experimental characterization combined with the theoretical calculation method demonstrates that VO-B/N-ZGO can show effective charge compensation more easily through the interaction of oxygen vacancies, interstitial boron, and substitutional nitrogen; especially for the formation of a B–N bond, it avoids the presence of semioccupied states as new recombination centers in a doped photocatalyst. In addition, VO-B/N-ZGO rich in reactive sites is generated by oxygen vacancy-modified B/N-codopi...

Long term in vivo imaging with Cr3+ doped spinel nanoparticles exhibiting persistent luminescence

Persistent luminescence is a singular property of some materials which are able to store the excitation or light irradiation energy at intrinsic traps or defects before slowly emitting lower energy photons within several hours. When such compounds are prepared as nanoparticles (NPs), when functionalization is realized to get colloidal materials well dispersed in aqueous medium, such nanoprobes open the use of the persistent luminescence for bioimaging applications. Recently, the numbers of in vivo applications increased with new modalities and new expectations.In this review, we focused our attention on the ZnGa2O4:Cr (ZGO:Cr) nanoparticles. When ZnGa2O4 (ZGO), a normal spinel is doped with Cr3+ ions, a high brightness persistent luminescence material with an emission spectrum perfectly matching the transparency window of living tissues is obtained. It allows in vivo mouse imaging with an excellent target-to-background ratio. One interesting characteristic of ZGO:Cr lies in the fact that its persistent luminescence can be excited with orange/red light, well below its band gap energy and in the transparency window of living tissues. This important property allows multiple re-excitations to perform long term bioimaging. Antisite defects of the direct spinel structure are assumed to provide shallow traps which store the excitation light. Charge release by room temperature thermal excitation and recombination center, here trivalent chromium, are responsible for the persistent luminescence. Following a primary excitation (UV or visible), one also observed that trapped charges can be released under 977nm light stimulation for several spinel gallate materials, therefore increasing the modalities and the materials envisioned for in vivo excitation of these NPs.

Chromium Doped Persistent Phosphors for Medical Imaging

Persistent luminescent materials or glow-in-the-dark compounds have been known for centuries, but due to their limited performance in terms of total light output, they were never used for large scale applications. It is only since about 20 years ago, when SrAl2O4:Eu,Dy was introduced as a new persistent phosphor [1], that a leap forward in both brightness and decay time was achieved. This paper has initiated substantial research, which has led to an entire family of materials, showing an appreciable afterglow for more than 24 hours [2,3]. These developments have opened up a whole new series of applications, ranging from emergency illumination, decoration and toys to medical imaging. For the latter application, materials are needed with deep red to near infrared emission, which falls in the transparency window of biological tissues. This, together with the need for red emitters for indicating emergency situations, has led to an interest in long wavelength persistent luminescence. Eu2+ is by far the most common dopant in persistent luminescent compounds. However, only very few chemically stable hosts are known, notably a number of nitrides, that allow to shift the Eu2+ emission to the deep red. Current research therefore focusses on Mn2+ and Cr3+ as valuable alternative dopants [4], as they allow to reach longer wavelengths than possible with Eu2+. Fig. 1: Principle of in vivo imaging using persistent luminescent materials. In this work, we will focus on Cr-doped ZnGa2O4 (ZGO), which is one of the most promising dopant-host combinations for near infrared emission [4]. ZGO has a normal spinel structure, where the Zn2+ and Ga3+ ions are located in octahedral and tetrahedral voids respectively. Due to their similarity with Ga3+ in charge and size, the Cr3+ ions occupy Ga-sites in the host. It has been shown that the trap states in ZGO:Cr, which are necessary to store the energy, liberated during the afterglow, are related to antisite defects: a small fraction of Ga-ions occupying Zn-sites or vice versa [5]. In addition, authors have tried to increase the number of traps by introducing different codopants and/or elements to form solid solutions with ZGO. This presentation will discuss different methods to synthesize ZGO:Cr nanoparticles which are potentially useful for in vivo medical imaging. In addition, the effects of different types of dopants on the defects and thus on the persistent luminescence will be presented. Finally, some alternative hosts for emission from Cr3+ - SrAl2O4 (ubiquitous in visible light persistent luminescence) and YAGG (yttrium aluminium gallium garnet) - are evaluated, and the toxicity of the materials, which is obviously very important for biocompatibility, is discussed. [1] T. Matsuzawa, Y. Aoki, N. Takeuchi and Y.A. Murayama, J. Electrochem. Soc. 143, 2670–2673 (1996). [2] K. Van den Eeckhout, P.F. Smet, D. Poelman, Materials 3, 2536-2566 (2010) [3] K. Van den Eeckhout, D. Poelman, P.F. Smet, Materials 6, 2789-2818 (2013) [4] Y.X. Zhuang, Y. Katayama, J. Ueda and S. Tanabe, Optical Materials 36, 1907-1912 (2014) [5] T. Maldiney, A. Bessière, J. Seguin, E. Teston, S.K. Sharma, B. Viana, A.J.J. Bos, P. Dorenbos, M. Bessodes, D. Gourier, D. Scherman, C. Richard, Nature Materials 13, 418-426 (2014) Figure 1

Non-aqueous sol-gel synthesis of ultra small persistent luminescence nanoparticles for near-infrared in vivo imaging.

Ultra-small ZnGa2 O4 :Cr(3+) nanoparticles (6 nm) that exhibit near-infrared (NIR) persistent luminescence properties are synthesized by using a non-aqueous sol-gel method assisted by microwave irradiation. The nanoparticles are pegylated, leading to highly stable dispersions under physiological conditions. Preliminary in vivo studies show the high potential for these ultra-small ZnGa2 O4 :Cr(3+) nanoparticles to be used as in vivo optical nanotools as they emit without the need for in situ excitation and, thus, avoid the autofluorescence of tissues.

Synthese Basse Temperature Du Gallate De Zinc

The dependence of the firing conditions on the crystal structure formation of ZnGa2 O4 has been investigated. The effects of temperature and atmosphere were examined and gave evidence of the instability of the zinc gallate under a reducing atmosphere at temperatures above 600°C. A new preparation route has allowed to synthesize ZnGa2 O4 at low-temperature, right from 300°C, avoiding the decomposition of the matrix during the annealing.

Growth and Analysis of Red, Green and Blue Luminescent Oxide Thin Films

The growth and characterization of europium ( Eu 3+) and terbium ( Tb 3+) doped yttrium aluminum garnet ( Y 3 Al 5 O 12 or YAG) and undoped ZnGa 2O4 photoluminescent thin films deposited on sapphire substrates at 400°C by excimer pulsed laser ablation is reported. Smooth, continuous 500-nm-thick amorphous films were produced with compositions depleted in oxygen. Luminescence measurements on the as-deposited and on annealed samples revealed that heat treatments at temperatures > 800°C were necessary to induce crystallization and reoxygenate, which coincided with the onset of luminescence. Annealing produced randomly oriented grains on the order of 15-200 nm.