Zinc Interstitials Research Articles

Zinc oxide-based sensor prepared by modified sol–gel route for detection of low concentrations of ethanol, methanol, acetone, and formaldehyde

Abstract We4 4 We received the acceptance date as 26 September 2024. Could you please update it to reflect this exact date for our project, instead of 1 October 2024? This is very important for our project funding. successfully synthesized zinc oxide (ZnO) nanoparticles using the sol–gel method, followed by their application onto alumina substrates for sensor testing. Comprehensive characterization of the nanomaterials was carried out utilizing XRD, SEM, TEM, UV–VIS-IR, and Photoluminescence (PL) techniques. The nanoparticles displayed a hexagonal wurtzite crystal structure, typical of ZnO. UV–Vis-IR spectroscopy revealed significant absorption in the UV region, with the band gap energy calculated to be 3.22 eV. PL spectra indicated the presence of various defects, such as oxygen vacancies and zinc interstitials, within the ZnO structure. SEM analysis of the deposited film surface showed spherical agglomerates, confirming the nanoscale dimensions, while energy-dispersive x-ray spectroscopy spectra affirmed the high purity of the ZnO films, rich in Zn and O elements. Sensor tests demonstrated the ZnO sensor’s high sensitivity to low concentrations of volatile organic compounds such as ethanol, formaldehyde, methanol, and acetone. Notably, at an operational temperature of 300 °C, the sensor exhibited a remarkable response to 5 ppm of each gas, with the following response and response/recovery times: for methanol, 11.47 and 36 s/57 s; for acetone, 11.54 and 25 s/52 s; for formaldehyde, 0.79 and 53 s/58 s; and for ethanol, 3.88 and 9 s/59 s.

Enhanced Photocatalytic Performance under Ultraviolet and Visible Light Illumination of ZnO Thin Films Prepared by Modified Sol-Gel Method.

Semiconductor oxides are frequently used as active photocatalysts for the degradation of organic agents in water polluted by domestic industry. In this study, sol-gel ZnO thin films with a grain size in the range of 7.5-15.7 nm were prepared by applying a novel two-step drying procedure involving hot air treatment at 90-95 °C followed by conventional furnace drying at 140 °C. For comparison, layers were made by standard furnace drying. The effect of hot air treatment on the film surface morphology, transparency, and photocatalytic behavior during the degradation of Malachite Green azo dye in water under ultraviolet or visible light illumination is explored. The films treated with hot air demonstrate significantly better photocatalytic activity under ultraviolet irradiation than the furnace-dried films, which is comparable with the activity of unmodified ZnO nanocrystal powders. The achieved percentage of degradation is 78-82% under ultraviolet illumination and 85-90% under visible light illumination. Multiple usages of the hot air-treated films (up to six photocatalytic cycles) are demonstrated, indicating improved photo-corrosion resistance. The observed high photocatalytic activity and good photo-corrosion stability are related to the hot air treatment, which causes a reduction of oxygen vacancies and other defects and the formation of interstitial oxygen and/or zinc vacancies in the films.

Stability of phase composition and properties of Zn4+xSb3 medium-temperature thermoelectric material

The phase composition and thermoelectric properties of a β-Zn4Sb3 based material before and after thermocycling tests at 273–723 K have been studied. Specimens with stoichiometric Zn and Sb molar ratios and with additions of different excess Zn quantities have been synthesized by direct component smelting followed by spark plasma sintering. The phase composition and structure of the materials have been studied using X-ray diffraction and transmission electron microscopy. The thermal conductivity and specific heat of the materials have been measured with laser flash and differential scanning calorimetry techniques. The phase composition of the as-synthesized, as-sintered and as-thermocycled Zn4+xSb3 thermoelectric material has been found to vary depending on excess Zn content in the charge. Excess Zn has been shown to dissolve in the β-Zn4Sb3phase upon spark plasma sintering and thermocycling. β-Zn4+xSb3 solid solution depletion of interstitial zinc atoms or ZnSb phase precipitation upon thermocycling increase the thermal conductivity and reduce the thermoelectric efficiency of the material. The Zn4.1Sb3 composition has shown high thermoelectric efficiency, the 715 K ZT being ∼1.23 and 1.18 before and after thermocycling, respectively.

Influence of FRET, charge separation, and density of defect states on the improvement of UV light-driven photocatalytic activity of PMMA capped ZnO nanomaterials

This study employs oxidative polymerization, co-precipitation, and ex-situ surface capping techniques to fabricate pristine PMMA, ZnO, and PMMA-capped ZnO specimens with varying PMMA concentrations. X-ray diffraction reveals reduced directional growth of ZnO, while Fourier transform infrared spectroscopy confirms PMMA chain bonding with ZnO in PMMA-capped specimens. Scanning electron microscopy illustrates decreased average length and thickness of ZnO nanoplates post-surface modification, indicating a robust interaction between PMMA and ZnO. X-ray photoelectron spectroscopy identifies suppressed defects, including zinc interstitials and oxygen vacancies, affirming ZnO surface capping by PMMA. Absorption spectra display a blue shift in band-edge or increased bandgap, attributed to the combined effects of band alignment offset and reduced oxygen vacancy states. Luminescence spectra show gradual quenching linked to PMMA content increase, with defect-related emission suppression attributed to ZnO surface capping. UV emission suppression is ascribed to donor concentration-dependent Förster resonance energy transfer (FRET) from PMMA to ZnO. Photocatalytic tests reveal enhanced efficiency in PMMA-capped ZnO catalysts attributed to synergies involving charge separation, bulk recombination centers, oxygen vacancy states, and FRET. Efficiency improves with higher PMMA content, aligning with changes in emission intensity. The study demonstrates emission intensities' tunability through surface capping and donor concentration-dependent FRET, ultimately influencing degradation efficiency.

Environmental-related applications of ZnO nanopowders: Photocatalytic activity and photoluminescence response to ethanol

Zinc oxide (ZnO) and copper-doped zinc oxide (ZnO:Cu) nanopowders were synthesized via solvothermal methods using methanol and hexamethylenetetramine (HMTA). Undoped ZnO nanopowders underwent calcination in O2-rich and H2-rich atmospheres at 600 °C. Samples were studied by scanning electron microscopy, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), and Raman, photoluminescence (PL) and UV–vis absorbance spectroscopies. The doping and calcinations led to a reduction of the optical bandgap of the nanopowders, while their structure remained hexagonal wurtzite with some changes in lattice parameters and average nanoparticle sizes. The Cu2+ doping led to a BET surface area and violet PL component increase. Samples were also examined for environmental related applications, namely as photocatalyzers for dye degradation and as ethanol optical sensors. For photocatalytic activity in methylene blue degradation under UV, H2-rich calcined powders excelled, with a rate constant of −0.076 min−1, surpassing −0.057 min−1 (ZnO:Cu), −0.056 min−1 (O2-rich calcination), and −0.041 min−1 (as-grown ZnO). We propose that this improvement can be attributed to the formation of ZnO/Zn interfaces stemming from the reduction of surface interstitial zinc by H2 during calcination, in addition to the observed reduction of the ZnO bandgap. The doped nanopowders PL also showed excellent response when exposed to ethanol vapor.

Fabrication of highly conducting undoped ZnO ceramics by flash sintering

Highly conducting undoped ZnO ceramics were fabricated by flash sintering using commercial pure ZnO powder as a model system. The flash-sintered samples with diameters of 15 mm and heights of 2 mm exhibited relative densities ranging from 93.6% to 97.1% and room-temperature electrical conductivities between 205 and 590 S/cm. X-ray diffraction and Raman spectra indicated a high concentration of oxygen vacancies and zinc interstitials in the flash-sintered samples, increasing the carrier concentration. Detailed microstructural analyses show that clean grain boundaries and the morphology and distribution of impurities in flash-sintered samples are favorable for improving carrier mobility. Additionally, flash sintering has the advantage of reducing conditions, which reduces acceptor defects at ZnO grain boundaries, lowers Schottky barriers, and increases carrier mobility. The results show that flash sintering can synergistically enhance the carrier concentration and mobility in ZnO ceramics, making it a promising technique for fabricating highly conducting ZnO ceramics.

The dependence of electrical conductivity of MgxZn1–xO ceramics on phase composition

The structural and electrical characteristics of (Mg,Zn)O ceramics produced using the solid state reaction at 1100 °C for 3 hours were studied applying X-ray diffraction and IR reflection spectroscopy as well as means of direct current measurements versus MgO content in initial charge (varied from 0 to 100 mol.%). It has been shown that electrical conductivity extracted from the IR reflection spectra corresponds to that of hexagonal phase in a solid solution, while plasmon in cubic phase was not observed. The electron concentration in the hexagonal grains of solid solution prepared with MgO content below 30 mol. % in the charge was found to be close to that of ZnO grains. It shows the tendency to decrease with further growth of the MgO content, which was explained by extraction of zinc interstitials, responsible for ZnO conductivity, from ZnO under formation of the MgZnO cubic phase. The direct current measurements have shown the lower conductivity as compared to the value estimated from IR reflection spectra. This fact along with the superlinearity of current-voltage characteristics has been explained by the presence of intergranular barriers, which does not allow obtaining information on the concentration of free electrons in the grain by this method. The possible nature of intergranular barriers as well as the role of grain boundaries in the DC conductivity of samples has been discussed.

Deep-Level Transient Spectroscopy Studies on Four Different Zinc Oxide Morphologies

In this work, we described the variations in the defect energy levels of four different ZnO morphologies, namely nanoribbons, nanorods, nanoparticles, and nanoshuttles. All the ZnO morphologies were grown on a seeded 4% Boron-doped p-type silicon (p-Si) wafer by using two different synthesis techniques, which are chemical bath deposition and microwave-assisted methods. The defect energy levels were analyzed by using the Deep-Level Transient Spectroscopy (DLTS) characterization method. The DLTS measurements were performed in the 123 K to 423 K temperature range. From the DLTS spectra, we found the presence of different trap-related defects in the synthesized ZnO nanostructures. We labeled all the traps related to the four different ZnO nanostructures as P1, P2, P3, P4, and P5. We discussed the presence of defects by measuring the activation energy (Ea) and capture cross-section (α). The lowest number of defect energy levels was exhibited by the ZnO nanorods at 0.27 eV, 0.18 eV, and 0.75 eV. Both the ZnO nanoribbons and nanoparticles show four traps, which have energies of 0.31 eV, 0.23 eV, 0.87 eV, and 0.44 eV and 0.27 eV, 0.22 eV, 0.88 eV, and 0.51 eV, respectively. From the DLTS spectrum of the nanoshuttles, we observe five traps with different activation energies of 0.13 eV, 0.28 eV, 0.25 eV, 0.94 eV, and 0.50 eV. The DLTS analysis revealed that the origin of the nanostructure defect energy levels can be attributed to Zinc vacancies (Vzn), Oxygen vacancies (Vo), Zinc interstitials (Zni), Oxygen interstitials (Oi), and Zinc antisites (Zno). Based on our analysis, the ZnO nanorods showed the lowest number of defect energy levels compared to the other ZnO morphologies.

Influence of compacting pressure on the electrical properties of ZnO and ZnO:Mn ceramics

Undoped and Mn-doped ZnO ceramics were prepared from the powders compacted at different pressures and sintered in air at high temperature. Their structural, optical, light emitting and electrical characteristics as well as the distribution of chemical elements were studied. It was found that an increase in compacting pressure stimulates an increase in direct current conductivity in both undoped and doped samples. In the case of doped samples, this effect was accompanied by a decrease in the height of potential barriers at the grain boundaries. It is found that electron concentration in ceramic grains, estimated from the modelling of infrared reflection spectra, remained relatively constant. The analysis of luminescence spectra and spatial zinc distribution revealed that the increase in compacting pressure results in the accumulation of interstitial zinc at the grain boundaries forming channels with enhanced conductivity. These findings provide an explanation for the evolution of electrical properties of ceramic samples with compacting pressure.

Inverse dynamic defect annealing in ZnO

Radiation tolerance of semiconductors depends on the dynamic defect annealing efficiency during irradiation. Consequently, it matters at what temperature one keeps the sample during irradiation, so that elevated temperatures typically result in lower remaining disorder. In the present work, we observed an opposite trend for the nitrogen ion implants into zinc oxide. Combining ion channeling technique, x-ray diffraction, and photoluminescence spectroscopy, we demonstrate that the interaction of nitrogen with radiation defects promotes an inverse dynamic annealing process, so that the increase in irradiation temperature leads to a more efficient defect formation. As a result, the residual radiation disorder is maximized at 650 °C and this state is characterized by the appearance of prominent optical signatures associated with zinc interstitials and strongly reduced strain accumulation as compared to the samples implanted at lower temperatures. However, for higher implantation temperatures, the impact of the inverse annealing decreases correlating with the surface degradation and loss of nitrogen.

Controlled evolution of surface microstructure and phase boundary of ZnO nanoparticles for the multiple sensitization effects on triethylamine detection.

In ZnO gas sensors, donor defects (such as zinc interstitials and oxygen vacancies) are considered active sites for the chemical adsorption and ionization of oxygen on the surface of ZnO, which can significantly enhance the sensor's response. However, the influence of the surface microstructure and phase boundaries of ZnO nanoparticles on the chemical adsorption and ionization of surface oxygen has rarely been explored. In this study, we developed a mixed-phase ZnO nanoparticle gas sensor with a rich phase boundary showing 198-50 ppm improvement in response to triethylamine at 340 °C. This is attributed to the generation of defects originating from lattice mismatch at the ZnO - zincite phase boundaries, which providing more active sites for adsorption of oxygen and triethylamine molecules. This work demonstrates a feasible method of combining surface microstructure regulation with pyrolysis strategies to develop ZnO sensors with significantly enhanced gas response performance.

NATURE OF ZINC OXIDE COLLOIDAL NANOCRYSTALS PHOTOLUMINESCENCE

The purpose of the study is to determine the nature of the radiative transitions responsible for the visible radiation of zinc oxide nanocrystals. Show that the size of nanocrystallites does not affect the spectral composition and location of long-wave luminescence. ZnO nanocrystals obtained by the method of colloidal synthesis with or without gelatin stabilization were investigated in the paper. The size of the nanocrystallites was determined in the approximation of the effective masses by the magnitude of the fundamental absorption edge shift. The results of calculating the size of nanocrystallites agree well with the results of SEM studies. It is shown that the main factor affecting the size of nanocrystallites is the concentration of precursors. Photoluminescence spectra of colloidal ZnO nanocrystals were studied in two spectral regions – ultraviolet and visible. Photoluminescence spectra in the ultraviolet region are characterized by three emission lines, the location of which depends on the concentration of precursors, that is, on the width of the band gap. Analysis of the energy states of intrinsic defects in nanostructured zinc oxide showed that the first two emission lines are associated with radiative transitions of excitons bound on neutral interstitial zinc atoms and on neutral zinc vacancies. The third line of ultraviolet radiation is caused by radiative transitions with the participation of deep donors, which are interstitial zinc atoms in the +2 charge state. The visible radiation spectra of colloidal ZnO nanocrystals are characterized by broad non-elemental emission bands in the blue-green and yellow-red regions of the spectrum. A detailed analysis of the spectra at different concentrations of precursors showed that the change in concentrations of precursors does not affect the spectral location of elementary emission lines. The absence of impurity absorption lines indicates that the centers responsible for visible radiation are donor-acceptor pairs. The analysis of the ratio of the emission lines intensities with increasing concentrations of the precursors shows that interstitial zinc and oxygen atoms dominate in the studied nanocrystals at high concentrations. As a result, in samples with a high concentration of precursors, blue radiation dominates over yellow and green. Thus, the study shows that by changing the concentrations of precursors, it is possible to influence both the spectral location of the edge ultraviolet luminescence and the intensity of individual long-wave luminescence components. The resulting colloidal ZnO nanocrystals can be used as luminescent sensors.

Investigation of Structural Electrophysical Parameters of ZnO al Films for Electronics

In this paper, the effect of the introduction of aluminum in concentrations 1—3 at was investigated. % in semiconductor nanostructured zinc oxide films obtained by sol-gel method. Based on the results of scanning electron microscopy, it was found that all samples have a branched structure, while there is a tendency for the branches to enlarge with an increase in the concentration of the modifier. Studies of optical transmission spectra have shown that the samples are transparent in the visible radiation range; the calculation of the optical band gap showed an increase in the amorphization of the material, which we associate with the for-mation of impurity levels formed by aluminum cations overlapping with the band conductivity, as well as an increase in the concentration of intrinsic point electrically active defects. Analysis of the results of the dependence of electrical conductivity on temperature showed its semiconductor nature and the presence of two regions with the following activation energies: the first region is a low—temperature region with low energy in the range of 35—75 meV; the second region is a high—temperature region with energy in the range of 0.35— 0.45 eV. We associate the low activation energy with donor levels of interstitial zinc Zni defects. At the same time, with an increase in the concentration of aluminum, the value of the activation energy of this level decreases, which is associated with the substitution of zinc atoms with aluminum and their displacement into the internode. The analysis of the electrical conductivity of the studied films in the range of 20...400 °C shows its maximum value at the concentration of the alloying impurity in 1 at. %. Thus, this composition is optimal from the point of view of obtaining transparent conductive films.

STRUCTURE, OPTICAL PROPERTIES AND PHOTOCATALYTIC ACTIVIYY OF UNDOPED, La2O3-DOPED ZnO NANOCOMPOSITES

La-doped ZnO nanocomposites with di­ffe­rent content of La2O3 (1–5%) were obtained by the Pechini method from their nitrate solutions. The solutions of Zn2+ and La3+ nitrates were preliminary obtained by dissolving of zinc and lanthanum oxides with a content of the main component of 99.99% in nitric acid. The influence of lanthanum doping the on the microstructure, morphology, optical pro­perties and photocatalytic activity of the ZnO nanopowders were examined. The properties of the nanopowders were studied by using X-ray phase analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy. The samples were subjected to X-ray powder diffraction using a DRON-3 diffractometer (Cu-K radiation) at room temperature. The scan angle was 0.05–0.1 ° in the range 2 = 15–90 °. X-ray phase ana­lysis confirms the formation of single phase of La2O3-doped ZnO powders on diffractograms. Raman light scattering and photoluminescence spectra were recorded using a Horiba Jobin‑Yvon T64000 spectrometer equipped with a CCD detector at room temperature in the inverse scattering geometry. According to SEM results, the powders characterized a conglomerate structure. The undoped ZnO has an average particle size of 43 nm, while the average particle size of La3+-doped ZnO ranges from 64 to 80 nm. It was established that the morphology of powder particles primarily depends on the content of La3+ in the material. An increase in the amount of La3+ in zinc oxide leads to an increase in the specific surface area (from 3.8 to 11.8 m2/g). In the photoluminescence spectra of ZnO powders, with increasing La2O3 concentration, bands at 400 nm are observed due to the appearance of impurities that cause of interstitial zinc and zinc vacancy defects and their broade­ning with a shift to the long-wave region. Photocatalytic properties of ZnO pow­ders doped with lanthanum oxide were in­vestigated using Methyl Orange as a model dye under Osram Ultra-Vitalux lamp (300 W) irradiation. A present result indicates that the obtained powders are potential candidate for the practical application in photocatalysis.

Nanostructural Design of ZnO Using an Agro-Waste Extract for a Sustainable Process and Its Photocatalytic Activity.

The use of agro-waste extracts (AWEs) as a sustainable medium for developing cost-effective and ecologically friendly nanomaterials has piqued the interest of current researchers. Herein, waste extracts from papaya barks, banana peels, thumba plants, and snail shells were used for synthesizing ZnO nanostructures via a hydrothermal method, followed by calcination at 400 °C. The crystallinity and pure wurtzite phase formation of ZnO nanostructures were confirmed via X-ray diffraction. ZnO nanostructures with various morphologies such as tight sheet-like, spherical, porous sheet-like, and bracket-shaped, comprising small interconnected particles with a highly catalytically active exposed (0001) facet, were observed via field emission scanning electron microscopy and transmission electron microscopy. The formation mechanism of the various morphologies of the ZnO nanostructures was proposed. Ultraviolet-visible spectra showed different absorption band edges of ZnO nanostructures with a bandgap in the range of 3.17-3.27 eV. Photoluminescence studies showed the presence of various defect states such as oxygen and zinc vacancies and oxygen and zinc interstitials on ZnO nanostructures, which are usually observed in traditionally prepared ZnO. The photocatalytic activity of ZnO nanostructures was evaluated under direct sunlight using rhodamine B (RhB) and Congo red (CR) dyes as probe pollutants. Furthermore, prepared ZnO nanostructures could potentially adsorb anionic dyes (e.g., CR) in the absence of light. Superoxide and hydroxide radicals played a vital role in the photocatalytic activity of ZnO. The photocatalyst could be reused for up to three cycles, indicating its stability. Therefore, this study reports the diverse use of AWEs as cost-effective media for nanomaterial synthesis.

Effect of graphene oxide coatings on the optical properties of pulsed laser deposited ZnO:Zn thin films

Highly c-axis orientated ZnO:Zn thin films were successfully prepared by pulsed laser deposition and coated with graphene oxide (GO) using nebulizer spray coating. The structural, morphological, and optical properties of the films were studied before and after annealing under different conditions to produce reduced GO (rGO). Following deposition on the surface of the ZnO:Zn films, the GO sheets showed non-uniform and defective textures. Heavily crumbled sheets were observed for rGO annealed in Ar, while wrinkled sheets were observed for rGO annealed in Ar/H2. The uncoated ZnO:Zn exhibited ultraviolet emission at ∼390 nm attributed to the recombination of excitons and a broad band in the range 400–600 nm centred at ∼450 nm attributed to zinc interstitials. The blue emission at ∼450 nm of ZnO:Zn was enhanced after coating with GO and/or rGO, which was attributed to the coupling of the light-emitting centres with localized surface plasmon resonances from the GO/rGO sheets. However, it was found that annealing of uncoated films also improved their luminescence intensity. These results showed that rGO/ZnO films may be useful for some optoelectronic or photoluminescence applications requiring ultraviolet and blue/green light.

Dynamics in between Structural and Electrical Properties of as Grown ZnO Thin Films by Thermal ALD

The mechanism behind n-type conductivity of undoped ZnO films are not understood well. One and two dimensional defects (grain boundaries, dislocations), and zero dimensional stoichiometric point defects (vacancies, self-interstitials and impurities) play a crucial role in determining the electrical properties of ZnO. All defect mechanisms are strongly controlled by the growth method and conditions. While it is more straightforward examining the one and two dimensional defects, measuring and unveiling the mechanism behind the zero dimensional point defect contribution and their sole effect on the electrical properties are challenging. This is why there has been controversial discussion of results among experimental and computational works relating physical and chemical properties of ZnO to sustainable electrical properties. In this study, to correlate the dynamics in between structural and electrical properties of ZnO grown by thermal ALD; growth temperature, DEZ and DI water precursor pulse times, DEZ/DI water precursor pulse ratio, and N2 purge time were varied. To obtain growth condition specific structural and electrical properties; XRD, AFM, profilometer, ellipsometry, XPS/CasaXPS, UV-VIS spectrometer, Hall-Effect measurements were utilized. Although, there was no strong correlation for oxygen vacancies, the contribution of hydrogen impurities, zinc interstitials and oxygen vacancies to conductivity was observed at different growth conditions. Lowest resistivity and highest average % transmittance were obtained as 6.8x10-3 ohm.cm and 92% in visible spectrum (380-700 nm), respectively.

Antimicrobial Agent Based on Ca‐Doped ZnO Nanopowders

Herein, sol–gel are used to synthesize pure and calcium‐doped ZnO (CZO). X‐ray diffraction shows that all samples have hexagonal wurtzite structure with a slight distortion of ZnO lattice and no extra secondary phases. The crystallite size increases after the addition of calcium from 31 to 34 nm. Photoluminescence shows the vanishment of the green emission band existed in the pure sample; in addition to the appearance of new peaks at 408, 448, 465, and 596 nm attributed to zinc interstitials (Zni), zinc vacancy (VZn), oxygen vacancy defect (Vo), and oxygen interstitial (Oi), respectively. The increase of crystallites size influences the efficacity of CZO sample against microbes. The different mechanisms to enhance the antibacterial activities are the release of Zn2+, reactive oxygen species production, and electrostatic interactions. Increasing the amount of CZO powder in dimethyl sulfoxide from 50 to 100 μg mL−1 leads to an increase of antibacterial activity of samples; and this is probably due to enhancement of number of interaction sites. Promising results are illustrated, which proves the potentiality of doping with Ca. The growth curves through optical density (OD600 nm) measurements of strains in CZO nanoparticles using serial fold dilution method indicated that strains viability decreases with increasing nanoparticles concentrations.

Full-spectrum and tunable white light emission of germanate glass-ceramic containing defective Zn2GeO4 and Mn2+ ions

The full-spectrum phosphors are key components for improving the light quality of phosphor-converted white light-emitting diodes (pc-WLEDs). In this work, a novel germanate glass-ceramic (GC) doped with Mn2+ was developed to achieve full-spectrum white light emission deriving from the defective Zn2GeO4 crystalline phase and Mn2+ with multisite occupancy. The defective Zn2GeO4 is crystallized in situ from the well-designed precursor germanate glass by a controllable heat treatment. The energy states of intrinsic defects, including oxygen and zinc vacancies and interstitial zinc and oxygen of Zn2GeO4 in GC, have been studied by first-principles calculations. The luminescence property and the energy transfer mechanism between the defect states and Mn2+ ions in the GC material was proposed. Under the UV excitation, the luminescence property can be tuned by adjusting the distribution of Mn2+ ions in between the glassy and crystalline phases. The correlated color temperature (CCT) and color rendering index (CRI) of the UV-excited full-spectrum white light emission can be tuned over a wide range. This combinatorial strategy of intrinsic defects and multisite ion doping for full-spectrum white light emission in GC, which overcomes the limitation of conventional discontinuous white light emitting materials that emit singly from doping ions, has shown good potential for application in pc-WLEDs.

Combined Effects of Ultraviolet Irradiation and Magnetic Field on the Properties of Dip-coated ZnO thin films

In this study, four ZnO thin films were deposited on FTO substrates using the sol–gel dip coating method to examine their microstructural, morphological, and optical properties through various techniques. Three of them were subjected to ultraviolet (UV) light, magnetic field (MF), and a combination of UV and MF during deposition, referred as ZnO: UV, ZnO: MF, and ZnO: (UV+MF), respectively. The results obtained showed that the simultaneous UV and MF exposure improved the crystallinity and surface homogeneity of the as-deposited film. Moreover, ZnO: (UV+MF) film exhibited an average transparency of 80% in the visible region and a high optical bandgap (3.67 eV). Room-temperature photoluminescence (PL) spectra revealed a weak UV emission and a strong violet emission peaks for all films. However, the violet emission intensity being lower in ZnO: UV and ZnO: MF films due to a reduction in zinc interstitials (Zni) defects, The simultaneous UV and MF exposure did not reduce Zni defects, and the violet emission intensity was almost identical to that of the untreated film. These findings suggest that the ZnO: (UV+MF) film can be a promising candidate for the development of ultraviolet and violet lasers and light-emitting diodes.