Red photoluminescence and blue-shift caused by phase transformation in multilayer films of titanium dioxide and zinc sulfide

The most versatile methods for altering the properties and behavior of materials involve a phase transformation in the solid state. In this article, we report multilayered films of ZnS/TiO2/ZnS on amorphous SiOx/Si substrates by pulsed laser deposition (PLD). After sequential vacuum annealing at various temperatures, we investigated the effects of TiO2 on the phase transformation of ZnS films and the consequential changes in photoluminescence (PL) property. PL spectra of the film revealed red emission centered at 686 nm after annealing at 600°C, however, this emission disappears, and the color shifts to blue after annealing at 700°C. Detailed analysis identified that TiO2 acts as a catalytic agent for the phase transformation of ZnS at this temperature, and that the color shift to blue resulted from decreased red emissions attributed to oxygen in the film. The present results show that catalytic agent-mediated phase transformation has strong potential for the modification of material properties. © 2015 Optical Society of America.1

Enhanced blue photoluminescence realized by copper diffusion doping of ZnO thin films

ZnO thin films with blue photoluminescence (PL) have been fabricated through Cu diffusion doping. A CuOx-ZnO mixture, and Cu/ZnO double layer, films were prepared on amorphous SiOx/Si substrates by pulsed laser deposition (PLD), and electron beam (e-beam) deposition, respectively. After sequential oxygen annealing, CuOx-ZnO mixture films exhibited green emission centered at 523 nm. However, Cu/ZnO double layer films differed in producing a blue emission centered at 480 nm. Detailed analysis identified that this blue shift in the emission center resulted from increased blue emissions attributed to Cu dopants in the film by e-beam deposition. Luminescence intensity was increased to 6 cd/m2 for a sample annealed at 700 deg;C. Color points were close to the locus of points following the line of a black-body-radiator on the CIE 1931 XY chromaticity diagram. The present results show that Cu-doped ZnO has strong potential as a cost effective phosphor for use in down converting LEDs. © 2013 Optical Society of America.1

Optical and photoelectric properties of Mn-doped ZnS thin film on a flexible indium-tin-oxide/polyethylene terephthalate substrate prepared by pulsed laser deposition

Optical and photoelectric properties of Mn-doped ZnS thin films on indium-tin-oxide (ITO)/polyethylene terephthalate (PET) substrates by pulsed laser deposition (PLD) were investigated. The XRD patterns revealed that the thin film deposited at room temperature (RT) had a wurtzite phase, which changed to a sphalerite phase at a substrate temperature of approximately 100°C. The transmittance of the films was approximately 87% in the visible range. The optical bandgap of the film deposited at RT was 3.29 eV, which increased to 3.361 eV with increasing substrate temperature to 200°C. The photoluminescence (PL) intensity at 468 nm and the photocurrent by UV irradiation increased in proportion to the substrate temperature. The present results imply that Mn-doped ZnS films deposited on flexible PET substrates are useful for fabricating flexible optoelectronic devices such as flexible UV detectors. © 2016 Optical Society of America.1

THE USE OF SPROUTED TRITICALE GRAINS IN FUNCTIONAL YOGURT TECHNOLOGY

The article discusses the results of studies of yogurt technology with the addition of crushed sprouted triticale grains. The optimal doses of plant components, organoleptic parameters and storage capacity were determined in the new functional product. The compositions of experimental samples of yogurt were selected: control - without additives; with the addition of 1.5%; 2% and 5% of crushed sprouted triticale grains. Yogurts with 1.5% and 2% of sprouted and crushed triticale grains were rated high according to the score. The addition of herbal additives to the formulation will expand the range, competitiveness; increases the nutritional, biological value and storage capacity, improves the organoleptic, physico-chemical functional and technological properties of the finished product

Effective control over near band-edge emission in ZnO/CuO multilayered films

We report on a study of the microstructural and photoluminescent properties of ZnO/CuO multilayered films. Multilayered ZnO/CuO thin films were deposited on amorphous SiO2/Si substrates by a pulsed laser technique and their microstructural and optical properties were characterized by transmission electron microscopy (TEM) and photoluminescence spectroscopy. TEM and XRD analyses of annealed ZnO/CuO films reveal the formation of multiple crystallographic defects and modification of the dominant growth plane, indicating effective doping of Cu atoms into the ZnO lattice. Consequently, near-band-edge emission in ZnO can be controlled through the number of CuO layers. Redshift of the near-band-edge emission peak from 385 nm up to 422 nm is achieved by increasing the number of CuO layers up to a certain number, above which a downward shift is observed. The results demonstrate that the emission properties of ZnO can be modified and precisely controlled by incorporation of CuO thin layers as a Cu-doping source. © 2017 Optical Society of America.1

Metal-Insulator Transition Detection of Vanadium Dioxide Thin Films by Visible Light Reflection

Vanadium dioxide (VO2)-based thin films have received considerable attention in recent years due to their superior performance in creating next-generation color-rendering materials. The near-room-temperature metal-insulator transition of VO2 promises the advantage of active color tuning in the visible wavelength range. Although various results of dynamic color generation combined with plasmonic nanostructures are currently being investigated, so far, very few studies have addressed the visible-light optical performance of pure VO2 thin films prepared on conventional substrates. This article shows in detail the phase transition behavior of VO2 thin films in the visible wavelength range of 400-750 nm prepared on glass with subsequent annealing at temperatures of 350, 400, 450, and 500 degrees C. The results show an anomalous phase transition reducing the overall RGB reflectivity correlated with the crystallization behavior of the VO2 phase and scattering effect. The sample annealed at 350 degrees C shows the smallest phase transition at 47 degrees C, correlating with a crystallite size of 7 nm. The blue band reflectivity anomaly after annealing at 450 degrees C was considered an effect of the secondary reflection. The results of this research could play a huge role in the production of active switching photonic devices, color-managed reflectors, and temperature indicators. © 2022 American Chemical Society. All rights reserved.FALS

Optical Properties of Cu-Doped ZnO Films Prepared by Cu Solution Coating

This work demonstrates the fabrication of Cu-doped ZnO films by Cu solution coating method. Cu ink was spin coated on ZnO thin films prepared by e-beam deposition. After curing and annealing at high temperatures, structural, morphological and optical properties of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectrofluorometer, respectively. The XRD results showed that ZnO films formed polycrystalline with a hexagonal wurtzite structure, and the grain size increased with increasing the annealing temperature from 500 to 850°C. The changes in lattice parameters were caused by grain size, strain, and residual stress. Morphological analysis have revealed that the Cu-doped ZnO film after annealing at 500°C has flat surface with uniformly distributed grain size, which became porous after higher temperature annealing process. Energy dispersive spectroscopy (EDS) and photoluminescence spectras have shown the presence of Zn, Cu, and O elements, and combined violet, blue, green and weak red emissions between 350 and 650 nm in the ZnO films, respectively. Copyright © 2015 American Scientific Publishers All rights reserved.