Zinc Germanate Research Articles

Influence of Crystallinity and Reaction Integrity on the Photoresponse of Silicon-Doped Zinc Germanate Nanowires

Influence of Crystallinity and Reaction Integrity on the Photoresponse of Silicon-Doped Zinc Germanate Nanowires

Dynamic Luminescence of Lead-Doped Calcium Zinc Germanate Clinopyroxene for Multimode Anticounterfeiting.

Anticounterfeiting plays an essential role in authenticating genuine documents and combating forged products. To further advance the anticounterfeiting technology, there is a strong demand to design new functional materials with unique properties that will be appropriate for making multimode complex security labels. Recently, dynamic security labels have emerged as a new type of advanced anticounterfeiting method as they can hold a much higher security level than the traditional static ones. In this work, we report that calcium zinc germanate (CZGO) clinopyroxenes doped with lead ions have several interesting optical properties, such as dynamic fluorescence, long persistent luminescence, and photochromism. We find that the concentration of lead dopants can significantly impact the reaction kinetics as well as the crystallinity and luminescence properties of CZGO phosphors. By fully utilizing these unique properties, we have successfully fabricated several security labels with multilevel information encoding and dynamic optical performance. The combination of multimode and dynamic luminescence makes these labels extremely challenging to illegally duplicate. With further optimization, this lead-doped CZGO clinopyroxene can be well-integrated into modern anticounterfeiting techniques that will generate highly secure anticounterfeiting labels to combat fake products.

Manganese-doped zinc germanate phosphors with vivid luminescent properties for anti-counterfeit applications

Fluorescent materials are commonly used in optical labels for anti-counterfeiting purposes. However, these well-known materials can be vulnerable to forgery. It is thus essential to develop new types of luminescent materials with unique optical properties. In this paper, we prepared metal-doped phosphor materials with an inorganic matrix using a high temperature solid-state reaction. The synthesized Mn-doped zinc germanate (ZGO:Mn) phosphors were characterized using various techniques, such as X-ray powder diffraction and photoluminescence spectroscopy, in order to understand their structural and optical properties. The ZGO:Mn phosphors exhibit green color fluorescence, persistent luminescence, and photostimulated luminescence (PSL), which are ideal for anti-counterfeiting applications. Several examples of using the PSL active materials on various substrates demonstrate their capability to prevent counterfeiting and forgery. We further showed that an iPhone can be used to reveal the ZGO:Mn-based security labels. This study contributes to the exploration of novel security materials and offers practical implications for the development of security and authentication technologies.

Persistent Luminescence Zn2GeO4:Mn2+ Nanoparticles Functionalized with Polyacrylic Acid: One-Pot Synthesis and Biosensing Applications.

Zinc germanate doped with Mn2+ (Zn2GeO4:Mn2+) is known to be a persistent luminescence green phosphor with potential applications in biosensing and bioimaging. Such applications demand nanoparticulated phosphors with a uniform shape and size, good dispersibility in aqueous media, high chemical stability, and surface-functionalization. These characteristics could be major bottlenecks and hence limit their practical applications. This work describes a one-pot, microwave-assisted hydrothermal method to synthesize highly uniform Zn2GeO4:Mn2+ nanoparticles (NPs) using polyacrylic acid (PAA) as an additive. A thorough characterization of the NPs showed that the PAA molecules were essential to realizing uniform NPs as they were responsible for the ordered aggregation of their building blocks. In addition, PAA remained attached to the NPs surface, which conferred high colloidal stability to the NPs through electrostatic and steric interactions, and provided carboxylate groups that can act as anchor sites for the eventual conjugation of biomolecules to the surface. In addition, it was demonstrated that the as-synthesized NPs were chemically stable for, at least, 1 week in phosphate buffer saline (pH range = 6.0-7.4). The luminescence properties of Zn2GeO4 NPs doped with different contents of Mn2+ (0.25-3.00 mol %) were evaluated to find the optimum doping level for the highest photoluminescence (2.50% Mn) and the longest persistent luminescence (0.50% Mn). The NPs with the best persistent luminescence properties were photostable for at least 1 week. Finally, taking advantage of such properties and the presence of surface carboxylate groups, the Zn2GeO4:0.50%Mn2+ sample was successfully used to develop a persistent luminescence-based sandwich immunoassay for the autofluorescence-free detection of interleukin-6 in undiluted human serum and undiluted human plasma samples. This study demonstrates that our persistent Mn-doped Zn2GeO4 nanophosphors are ideal candidates for biosensing applications.

A multicomponent lithium aluminum zinc germanate glass influenced by copper ions in its dielectric and spectroscopic characteristics

Multi component Li2O–Al2O3– ZnO–GeO2 glasses doped with CuO ranging from 0 to 1.0 mol% were prepared by the conventional melt quenching technique. Spectroscopic (optical absorption, IR, and EPR) and dielectric properties of the prepared glasses were examined. The EPR and optical absorption studies indicate that low-concentration CuO samples contain both Cu2+ and Cu + ions. CuO concentrations up to 0.6 mol% increased the level of disorder in the glass network, as indicated by IR studies. The dielectric study reveals the influence of copper valance states on the structural aspect of the samples. It has been shown from all these studies that the copper ions can be present in Cu3+ state in these glasses as well as Cu2+ and Cu+ states and thus participate in glass network formation. A quantitative analysis of the dielectric properties of the glasses has indicated that when the CuO concentration exceeds 0.6 mol%, the insulating strength increases. As a result, aluminum ions have been found to be tetrahedrally coordinated instead of octahedral. CuO concentrations above 0.6 mol% in the glass matrix significantly alter the physical properties of these glasses. The reduction of Cu2+ ions to Cu + ions has significantly effected the spectroscopic and dielectric investigations.

Calcium Doped Self-activated Zinc Germanate Long Afterglow Materials: Multicolor Afterglow and Application in Dynamic Anti-counterfeiting

Calcium Doped Self-activated Zinc Germanate Long Afterglow Materials: Multicolor Afterglow and Application in Dynamic Anti-counterfeiting

Shedding Light on the Structure and Characterization of K2ZnGe2O6: A Phase-Matchable Nonlinear Optical Crystal.

Nonlinear optical (NLO) materials have recently aroused great interest owing to their capability of frequency conversion in solid-state lasers. Herein, we report an acentric zinc germanate K2ZnGe2O6 obtained successfully through spontaneous crystallization methods. It affords a novel three-dimensional (3D) framework comprised of [GeO4] and [ZnO4] motifs with K atoms located in the tunnels. K2ZnGe2O6 displays a moderate second-harmonic-generation (SHG) intensity (0.73 × KDP) with phase-matchable behavior. Optical characterization demonstrated that it has a UV cutoff edge located at 368 nm with a large energy band of 3.23 eV, accompanied by a wide transmission window, covering a 3-5 μm atmospheric window. Moreover, thermal properties implied that it possesses intriguing thermal stability of 987 °C and a congruent melting nature. Additionally, first-principles calculations unveiled that the NLO performance was primarily attributed to the collective effect of [GeO4] and [ZnO4] building units. These findings indicate that K2ZnGe2O6 is a potential NLO crystal.

Analysis of the structure and luminescence properties of Zn2 GeO4 :Eu3+ according to Judd-Ofelt theory.

The preparation and characteristic of nanorod-like Zn2 GeO4 doped with Eu3+ or zinc germanate (ZGO):xEu3+ (x = 0 ÷ 0.05), which was synthesized using the hydrothermal method, are described. The influence of Eu3+ -doping ions on the structure and the optical properties of ZGO was also investigated. According to the photoluminescence spectra, ZGO:xEu3+ nanophosphors gave a red emission due to the 5 D0 →7 F2 emission of Eu3+ ions. In accordance with Judd-Ofelt theory, the intensity parameters for f-f transitions from the emission and absorption spectrum were determined. At the 5 D0 excited state of Eu3+ , total spontaneous emission probabilities (AR ), lifetimes (τR ), branching ratios (βR ), and quantum efficiency (η) were calculated. The ZGO:xEu3+ (x = 0.02, 0.03, 0.04) phosphor showed the branch ratio β (5 D0 →7 F2 ) > 60%, indicating that the phosphors prepared here have a promising potential as laser light. The sample with a concentration of 0.04Eu3+ achieved the highest quantum efficiency of 84%, suggesting that it has potential light-emitting diode applications.

Investigations on the Synthesis, Crystal Structure, Linear- and Nonlinear-Optical Properties of the Zinc Germanate Rb2ZnGe2O6.

A quaternary nonlinear-optical (NLO) zinc germanate, Rb2ZnGe2O6 (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group C2221 (No. 20) and features a 3D framework formed by GeO4 tetrahedra, ZnO4 tetrahedra, and Rb+ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH2PO4. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.

Intense Blue Chromophores in Cobalt Doped Phenacite‐Type Zinc Germanate System through Jahn‐Teller Distortion of Co Tetrahedron

AbstractIn the quest for new blue chromophores with less usage of cobalt alternatives to the carcinogenic and expensive zinc‐cobalt aluminate system, we developed cobalt doped phenacite type zinc germanate system. Rietveld analysis reveals that the CoO4 tetrahedron intensely experienced Jahn‐Teller distortions leading to irregular geometry on substitution. The UV‐vis‐IR absorption spectra exhibit intense Co2+ d‐d transitions with three fold splitting associated with the CoO4 tetrahedron in the visible and IR region, indicating low symmetry. The crystal field strength 10Dq, Racah parameter and Nephelauxetic ratio variations reflect on the improved covalency of the Co2+ environment. Thus the synergetic effect of Jahn‐Teller distortions and covalency of the CoO4 tetrahedron lead to strong absorptions in the green to red region resulting in intense blue colors with low cobalt content (2.2 to 8.9 mol %). The typical composition Zn1.6Co0.4GeO4 exhibits intense blue hue b*=−58.64, much higher than that of the commercial CoAl2O4 system.

Synthesis and electrochemical properties of zinc germanate nanowires as novel anode material for lithium-ion battery

Synthesis and electrochemical properties of zinc germanate nanowires as novel anode material for lithium-ion battery

Color Tunable Emission of Y3Al5O12:Ce3+ and Sm3+‐Doped Zinc–Germanate–Tellurite Glass Nanocomposite Powders and Coatings for Light‐Emitting Diodes Applications

A series of nanocomposite (NC) powders and coatings of ZnO–GeO2–TeO2:xSm3+ glass and Y3Al5O12:Ce3+ nanoparticles (YAG:Ce) are fabricated. Samarium ions concentration of the glass phosphor is varied with x values of 0.3, 1.0, 3.0, and 5.0 mol%. The powder batches are prepared with a 95/5 mass ratio of glass/YAG:Ce and uniaxially pressed to obtain powder pellets that are heat‐treated at 350 °C. Morphology and structural characterization are conducted through X‐ray diffraction analysis, scanning electron microscopy, and Raman spectroscopy. The photoluminescence properties of NCs are investigated under different wavelengths of 340, 403, and 460 nm, showing a global emission tonality in the reddish‐orange and yellowish‐green region according to the estimated CIE 1931 chromaticity coordinates. Also, NC coatings soda–lime glass slides are fabricated, and their photoluminescence is characterized using an UV light‐emitting chip (≈365 nm) and a blue light‐emitting chip (≈460 nm). The global emission under UV and blue light from the light‐emitting diode (LED) chips of the NC coatings shows a color tunability in the warm white light and yellowish‐green region.

Understanding the UV luminescence of zinc germanate: The role of native defects

Achieving efficient and stable ultraviolet emission is a challenging goal in optoelectronic devices. Herein, we investigate the UV luminescence of zinc germanate Zn2GeO4 microwires by means of photoluminescence measurements as a function of temperature and excitation conditions. The emitted UV light is composed of two bands (a broad one and a narrow one) associated with the native defects structure. In addition, with the aid of density functional theory (DFT) calculations, the energy positions of the electronic levels related to native defects in Zn2GeO4 have been calculated. In particular, our results support that zinc interstitials are the responsible for the narrow UV band, which is, in turn, split into two components with different temperature dependence behaviour. The origin of the two components is explained on the basis of the particular location of Zni in the lattice and agrees with DFT calculations. Furthermore, a kinetic luminescence model is proposed to ascertain the temperature evolution of this UV emission. These results pave the way to exploit defect engineering in achieving functional optoelectronic devices to operate in the UV region.

Observation of anomalous phase transition and band gap shrinkage in zinc germanate nanorods

This work reports the high temperature anomalous phase transition with high dielectric constant and low band gap in pure zinc germanate (Zn2GeO4) nanorods. Crystal structure of Zn2GeO4 nanorods were analyzed by X-ray powder diffraction and Raman studies. Electron microscopy reveals that nanorods have average diameter and length of 30 nm and 100 nm, respectively. UV–ViS study indicates low band gap of 3.96 eV. The observed dielectric constant is 40 times higher than bulk Zn2GeO4. High dielectric constant of ~772 and phase transition was observed around 400 °C. In the low and high temperature range, activation energy were ~0.33 and 1.34 eV. High dielectric constant and shrinkage in bang gap with temperature phase transition of Zn2GeO4 nanorods makes it the potential candidate for nano-optoelectronic and nanodevices applications in near future.

Zn2GeO4/SnO2 Nanowire Heterostructures Driven by Plateau–Rayleigh Instability

Herein, we report the formation of a particular core-shell structure, with a zinc germanate (Zn_2GeO_4) nanowire core and a discontinuous shell of SnO_2 nanocrystals, obtained in a single-step process. We propose a growth model that combines the Plateau-Rayleigh mechanism to produce a pattern of amorphous germanium oxide (a-GeO_2) particles along the Zn_2GeO_4 nanowire and the subsequent growth of well-faceted SnO_2 crystals when the nanowire orientation meets good lattice matching conditions. In this latter case, the linear array of a-GeO_2 particles acts as nucleation sites for the SnO_2 crystallites, leading to a skewer-like morphology that retains the periodicity of the Plateau-Rayleigh process. Otherwise, nanowires with different orientations appear decorated with a pattern of a-GeO_2 beads mimicking a necklace. Atomic resolution electron microscopy has been used to characterize the Zn_2GeO_4/SnO_2 nanoheterostructures. In addition, optical confinement effects have been observed in the luminescence maps and spectra, which have potential for further exploitation in the design of optical microcavities.

Alternating Current‐Driven Oxide Powder Electroluminescent Device Employing Vertically Aligned ZnO Nanowire Array

A novel type of AC‐driven oxide powder electroluminescent (EL) device is demonstrated. The device is based on stable heterogeneous junctions between Mn2+‐activated zinc germanate (Zn2GeO4:Mn) oxide phosphor and a vertically aligned ZnO nanowire array. The ZnO nanowire array is synthesized on an ITO‐coated glass substrate via a hydrothermal growth method. A stable phosphor–nanowire junction is formed by simple drop‐coating of a Zn2GeO4:Mn oxide phosphor suspension on the nanowire layer followed by annealing at 400 °C for 3 h. Bright green light (≈20 cd m−2) with a wavelength of 535 nm from the as‐fabricated EL device is observed, and the as‐fabricated device shows excellent stability in air, maintaining a brightness of ≈10 cd m−2 for 15 days with less than 2.5% intensity loss. The electroluminescence emission mechanism is discussed in detail. This new and facile strategy to build an oxide powder EL device can enable cost‐effective, highly stable, and energy‐efficient devices for lighting or display applications.

Correlative Study of Vibrational and Luminescence Properties of Zn2GeO4 Microrods

The optical properties of zinc germanate microrods are investigated and correlated with vibrational modes of the crystalline structure. The samples are grown by a thermal evaporation method using ZnO and Ge as precursors. Polarized Raman spectroscopy and polarized micro‐photoluminescence techniques are applied in order to shed some light into the origin of the luminescence in Zn2GeO4. Oxygen defects are usually responsible for light emission in most of semiconducting oxides. Here, the authors report two luminescence bands at room temperature, a broad green one at about 2.4 eV and an ultraviolet one at 3.2 eV, which are of composed nature. In addition, the authors observe changes in the Raman and PL spectra recorded with polarizers oriented parallel or orthogonal to the microrod axis. The evolution of the luminescence bands in Zn2GeO4 and their correlation with the observed Raman modes (O‐Ge‐O and Ge‐O‐Zn vibration modes) are discussed in the framework of oxygen defects in the Zn2GeO4 structure.

Oxygen-Vacancy-Activated CO2 Splitting over Amorphous Oxide Semiconductor Photocatalyst

Gaseous oxides generated during industrial processes, such as carbon oxides (COx) and nitrogen oxides (NOx), have important effects on the Earth’s atmosphere. It is highly desired to develop a low-cost and efficient route to convert them to harmless products. Here, direct splitting of gaseous oxides was proposed on the basis of photocatalysis by an amorphous oxide semiconductor. As an example, splitting of CO2 into carbon and oxygen was achieved over amorphous zinc germanate (α-Zn-Ge-O) semiconductor photocatalyst under 300 W Xe lamp irradiation. Electron paramagnetic resonance and 18O isotope labeling indicated that the splitting of CO2 was achieved via photoinduced oxygen vacancies on α-Zn-Ge-O reacting and thus filling with O of CO2, while the photogenerated electrons reduced the carbon species of CO2 to solid carbon. Under irradiation, such a defect reaction is sustainable by continuous photogenerated hole oxidation of surface oxygen atoms on α-Zn-Ge-O to form oxygen vacancies and to release O2. When ...

Structural and optical properties of germanium-doped zinc oxide nanorods as a function of annealing temperature

ABSTRACTZinc oxide nanorods with germanium doping were prepared by ion implantation and annealing treatment method, the microstructural and optical properties of which were studied by means of the X-ray diffraction, photoluminescence, and transmission electron microscopy measurements. The pristine sample exhibited a remarkable ultraviolet emission owing to the band edge emission from the zinc oxide matrix, indicated a good crystalline quality. Three emission peaks appeared after germanium ions were doped into zinc oxide nanorods. The 513 nm photoluminescence peak was ascribed to the transition between the vacancy defect in zinc oxide matrix. Photoluminescence peaks located at 548 and 778 nm were ascribed to germanium ions luminescence center in zinc germanate grain and germanium monoxide luminescence center. The light emission tuning was obtained by germanium doping and annealing treatment, which may help the development of the practical optoelectronic devices based on zinc oxide nanomaterials.

Synthesis and optical properties of Zn2GeO4 microrods

Zinc germanate (Zn2GeO4) microrods have been grown by a catalyst free thermal evaporation-deposition method. The microrods, with lengths of up to hundreds of microns have hexagonal cross section and faceted tips with morphologies in agreement with the rombohedral crystal structure of the germanate. Photoluminescence (PL) of the structures shows a broad band centered at about 2.4 eV, which is found by Gaussian deconvolution to consist of three components. A luminescence band at higher energies, centered at about 3.45 eV, is revealed by excitation with 20 kV electrons in the scanning electron microscope (SEM) or by PL under high excitation conditions. Resonance peaks observed in the luminescence spectra have been interpreted by the formation of Fabry–Perot modes in the hexagonal cross section of the rods. The waveguiding behavior of the rods has been assessed by excitation with a 325 nm laser and by detection of the excited luminescence emission transmitted along the rod. Micro Raman spectra of the rods show four bands in the range 740 cm−1–820 cm−1, with the most intense one peaked at 801 cm−1. Comparison with Raman spectra of GeO2 and of other germanates suggests that this set of bands, characteristic of Zn2GeO4 is related to vibrations of Ge–O bonds.