Vis NIR Region Research Articles

Synthesis of Acenaphthene Fused Dithiaporphyrin(3.1.1.1)s and N-Fused Triphyrin(3.1.1)s in One-Pot Condensation.

Two different types of novel nonaromatic acenaphthene fused macrocycles such as acenaphthene fused dithiaporphyrin(3.1.1.1)s and acenaphthene fused N-fused triphyrin(3.1.1)s were synthesized in one pot condensation reaction using 5,6-dibromoacenaphthene as a key precursor. The X-ray analysis revealed the oval core-shaped structure for dithiaporphyrin(3.1.1.1)s and intramolecular ring fusion in N-Fused triphyrin(3.1.1)s. The NMR, absorption and DFT studies suggested the non-aromatic nature of both macrocycles which absorb strongly in visible-NIR region. Both macrocycles were stable under electrochemical conditions and showed their electron-rich nature.

TiN/TiO2 embedded in ReS2 nanoflowers with wide light absorption and multi-interfacial charge transfer for efficient photocatalytic hydrogen generation

The design of functional materials with efficient light absorption and charge separation is crucial for photocatalytic energy conversion. Herein, a plasmonic TiN/TiO2/ReS2 ternary hybrid is prepared, which exhibits exceptional photocatalytic activity caused by the plasmon-mediated light absorption and multi-interfacial charge separation. The ternary hybrids were synthesized by heating TiN, Re, and S sources at high pressure and temperature. The TiN was partially oxidized to form TiN/TiO2 hybrids, which were then embedded in ReS2 nanoflowers through Ti-S bonds, creating a 3D flower-like structure with multiple interfaces. The plasmon resonance of TiN and the bandgap excitations of ReS2 and TiO2 endow the hybrids with efficient light absorption in UV–VIS-NIR region. Additionally, the novel embedded structure and the multiple interfaces between TiN, TiO2, and ReS2 facilitate the formation of built-in electric fields and multi-channel charge transfer, which efficiently quicken photoinduced carriers’ migration and hot electron injection. Consequently, the TiN/TiO2/ReS2 hybrids demonstrate a high-efficiency photocatalytic hydrogen generation rate, which is 12.1 times that of commercial P25. Notably, the hybrids also exhibit high photocatalytic activity under near-infrared light irradiation. This study offers innovative insights into the design of photocatalysts and suggests that the prepared materials could be utilized in solar-driven energy conversion applications.

Symmetric engineered central cross-shaped broadband metamaterial absorber with high absorption and stability for solar sailing and solar energy applications

We propose a theoretical design and analysis of a broadband metamaterial absorber (MMA) with significant potential for solar sailing applications which is a method of spacecraft propulsion that usages the momentum of sunlight to propel a spacecraft through space. The absorber features a metal-dielectric-metal configuration with a tungsten (W) based resonator and ground plane, and a Silicon-dioxide (SiO₂) substrate. Addressing the critical need for materials that can efficiently harness solar radiation for propulsion in space, our design achieves an average absorption of 99.15 % over a broad spectrum from 250 nm to 1200 nm, covering the UV–Visible–NIR regions, with near-unity absorption peaks at 362 nm and 915.8 nm. It maintains high absorptions of 84.9 % and 86 % under transvers electric and transvers magnetic modes respectively, demonstrating excellent wide incident angle stability and polarization insensitivity due to its symmetric design. PCR values close to zero confirm its functionality as an absorber rather than a polarizer. The MMA shows minimal deformation across temperatures from 500 K to 1750 K and remains stable under various mechanical stresses, proving its durability and efficiency in space. Additionally, in solar thermophotovoltaic (STPV) systems, the MMA demonstrates high photothermal conversion efficiency (PTCE) over a wide temperature range (500 °C to 1500 °C) and different concentration factors. This dual functionality highlights its potential for both efficient space exploration and terrestrial solar energy harvesting, making it a versatile tool for future technological applications.

Photothermal manipulation of the fringing field in gold nanorod dimers towards the apoptosis of cancerous cells

The possibility of coherent manipulation of optical and thermal energies in noble metal nanostructures has given birth to an enduring research arena coined by thermoplasmonics. Upon interaction with electromagnetic radiation, the energy of the produced hot electrons in metallic nanostructures is converted into heat and is transferred to the medium as a consequence of numerous relaxation processes. Gold nanorods have, often, been adopted as the classical anisotropic nanostructures owing to excellent shape-selective plasmonic tunability in the vis–NIR region. When a pair of metallic nanostructures are sufficiently close to each other to imbue electromagnetic interaction, there occurs evolution of collective plasmon modes, substantial enhancement of near field and strong squeezing of electromagnetic energy at the interparticle spatial region of the dimeric nanostructures. Recent advances in the ‘tips and tricks’ guide to assembling, even, anisotropic nanostructures in colloidal dispersions have offered the opportunity to interplay with the phenomenological plasmonic and thermal characteristics. The photothermal attributes emerging due to electromagnetic coupling of fringing fields have been explored considering parallel and perpendicular configurations of gold nanorod dimers as the prototypical systems from theoretical and experimental perspectives and their biomedical consequences have been realised in a mice model towards the photothermal apoptosis of cancerous cells.

Use of optical absorption and scattering properties to monitor the change of chemical characteristics, particle structure and viscoelasticity during apple puree processing

This work explored the optical absorption (μa) and reduced scattering (μs') properties at 400–1050 nm (Vis-NIR) and 900–1650 nm (SWIR) of apple puree at different heating times to evaluate their changes in composition and structure. The optical absorption and scattering coefficients of μa and μs' decreased with increasing heating time. The specific μs' coefficients at 432 nm, 455 nm, 1183 nm and 1304 nm were related to particle structural changes. The partial least squares regression (PLSR) models based on μs' coefficients in the combined Vis-NIR and SWIR regions provided satisfactory estimations of puree particle area (Rp2 = 0.90) and particle perimeter (Rp2 = 0.85), whereas the μs' coefficients in the Vis-NIR region predicted puree viscosity (Rp2 = 0.83), elasticity modulus (Rp2 = 0.81) and viscous modulus (Rp2 = 0.78). Consequently, optical properties can be a potential tool to determine structural and rheological changes of apple puree.

Synthesis, Studies of Inorganic Class of Mohrite (MOH) Crystals for Electrical, Electronic, Photonic, Phase Matching and Sensor Utilities by Theory and Practice

The high-quality single crystals of Mohrite (MOH) with dimensions 7 × 6 × 3 mm3 were productively grown-up by the customary solution growth methodology. The fully grown crystals were focused to the appropriate structural, optical and electrical investigations. The MOH is monoclinic nature of the specimen with P21/c as the space group and lattice parameters are a as 6.2385 Å, b as 12.6076 Å, c as 9.2655 Å and beta is 106.526°. The crystalline structural authentication with single crystal XRD analysis and compared the same with software based associated results. FITR spectra reveal the vibrational modes of as grown crystals. Optical absorption spectral data divulges that the as-grown crystalline sample has higher optical transparent nature in the visible-NIR region. Photoluminescence intensity is remarkably enriched, shows high crystallinity of MOH. The results of UV, PL, electrical and photo conductivity, SEM, theoretical studies suggest MOH in photonic utility and device appliances especially in UV filters and in electronic filters, room temperature based sensor study for MOH is enabled and reported for red LED based work.

Exploring the Structural, Optical and Photoluminescence Performances of CuCo2O4 and ZnMn2O4 Alloying

The performance of the structural, linear/ nonlinear optical and photoluminescent properties of CuCo2O4 and ZnMn2O4 alloying was investigated. (1−x)CuCo2O4/(x)ZnMn2O4 (x = 0, 0.10, 0.15, 0.2) samples were prepared by the sol-gel and hydrothermal procedures. Synchrotron X-ray diffraction measurements were employed to investigate the structural and microstructural properties applying the Rietveld refinement method. Fourier transform infraed and Raman techniques were applied to explore the structures’ variation and chemical bonding of the obtained phases. Ultraviolet–visible diffuse reflectance spectroscopy measurements were collected to explore the optical properties. The optical band gap values were determined using the Kubelka-Munk method. All samples exhibited two band gaps in the visible-NIR regions. Upon composing with ZnMn2O4, the band gaps of CuCo2O4 declined for x = 0.1 and 0.15, followed by an increase at x = 0.2. The possible electronic band structure of the samples and the photoluminescent performance of the prepared samples was investigated. The observed PL patterns manifest wide and asymmetrical emissions. The CIE chromaticity diagram for all samples was plotted. The obtained findings of (1−x)CuCo2O4/(x)ZnMn2O4 nominate their efficient role in optical device fabrication and photocatalyst applications.

The Modeling of Concentrators for Solar Photovoltaic Systems

Concentrating photovoltaic (CPV) systems have emerged as a transformative technology that incorporates radiation concentrators into the photovoltaic system to enable radiation to be concentrated onto a receiver—the solar cells. Different concentrator configurations have different impacts on the performance of the solar photovoltaic system. This research work aims to analyze the impact of different concentrators, comparing and identifying the most efficient structures for capturing and concentrating solar energy. Aiming at a deep analysis and comparison among concentrators shapes, this research work presents a unique investigation and revision among different structures such as flat, triangular, LFR, and parabolic concentrators. Moreover, since, in the UV–visible–NIR region, metals’ reflectance varies with the incident wavelength, five metals were considered: aluminum, gold, platinum, copper, and silver. Additionally, the research focuses on studying the effects of parameters critical to the quality of the concentration on the power obtained and on the uniformity of the radiation distribution on the surface of the receiver, as well as on the number of solar rays that reach the receiver. The power on the receiver increases proportionally with the number of reflector concentrators in the system and their reflectance. For parabolic geometries, the optical efficiency is affected by the receiver’s shadow on the concentrator and, in the case of the LFR, by a non-ideal alignment of the reflectors in relation to the receiver. However, in parabolic concentrator geometries, uniformity is usually lower, since in these configurations, the radiation is focused on specific areas of the receiver, usually the central zone.

Spectroscopic and Thermographic Qualities of Praseodymium-Doped Oxyfluorotellurite Glasses.

The thermal stability of oxyfluorotellurite glass systems, (65-x)TeO2-20ZnF2-12PbO-3Nb2O5-xPr2O3, doped with praseodymium was examined. The different concentrations of praseodymium oxide (x = 0.5 and 2 mol%) were applied to verify the thermal, optical and luminescence properties of the materials under study. The relatively high values of the Dietzel (ΔT) and Saad-Poulain (S or H') thermal stability factors determined using a differential thermal analysis (DTA) indicate the good thermal stability of the glass matrix, which gradually improves with the content of the active dopant. The temperature dependence of optical spectra in the temperature range 300-675 K for the VIS-NIR region was investigated. The involved Pr3+ optical transition intensities and relaxation dynamic of the praseodymium luminescent level were determined. The ultrashort femtosecond pulses were utilized to examine a dynamic relaxation of the praseodymium luminescent levels. Although the measured emission of the Pr3+ active ions in the studied glass encompasses the quite broad spectral region, the observed luminescence may only be attributed to 3PJ excited states. As a result, the observed decrease in the experimental lifetime for the 3P0 level along with the increasing activator content was identified as an intensification of the Pr-Pr interplay and the associated self-quenching process. The maximum relative sensitivities (Sr) estimated over a relatively wide temperature range are ~0.46% K-1 (at 300 K) for FIR (I530/I497) and 0.20% K-1 (at 600 K) for FIR (I630/I497), which seems to confirm the possibility of using investigated glasses in optical temperature sensors.

Characterization of the TCO Layer on a Glass Surface for PV IInd and IIIrd Generation Applications

In the dynamic field of photovoltaic technology, the pursuit of efficiency and sustainability has led to continuous novelty, shaping the landscape of solar energy solutions. One of the key elements affecting the efficiency of photovoltaic cells of IInd and IIIrd generation is the presence of transparent conductive oxide (TCO) layers, which are key elements impacting the efficiency and durability of solar panels, especially for DSSC, CdTe, CIGS (copper indium gallium diselenide) or organic, perovskite and quantum dots. TCO with low electrical resistance, high mobility, and high transmittance in the VIS–NIR region is particularly important in DSSC, CIGS, and CdTe solar cells, working as a window and electron transporting layer. This layer must form an ohmic contact with the adjacent layers, typically the buffer layer (such as CdS or ZnS), to ensure efficient charge collection Furthermore it ensures protection against oxidation and moisture, which is especially important when transporting the active cell structure to further process steps such as lamination, which ensures the final seal. Transparent conductive oxide layers, which typically consist of materials such as indium tin oxide (ITO) or alternatives such as fluorine-doped tin oxide (FTO), serve dual purposes in photovoltaic applications. Primarily located as the topmost layer of solar cells, TCOs play a key role in transmitting sunlight while facilitating the efficient collection and transport of generated electrical charges. This complex balance between transparency and conductivity highlights the strategic importance of TCO layers in maximizing the performance and durability of photovoltaic systems. As the global demand for clean energy increases and the photovoltaic industry rapidly develops, understanding the differential contribution of TCO layers becomes particularly important in the context of using PV modules as building-integrated elements (BIPV). The use of transparent or semi-transparent modules allows the use of building glazing, including windows and skylights. In addition, considering the dominant position of the Asian market in the production of cells and modules based on silicon, the European market is intensifying work aimed at finding a competitive PV technology. In this context, thin-film, organic modules may prove competitive. For this purpose, in this work, we focused on the electrical parameters of two different thicknesses of a transparent FTO layer. First, the influence of the FTO layer thickness on the transmittance over a wide range was verified. Next, the chemical composition was determined, and key electrical parameters, including carrier mobility, resistivity, and the Hall coefficient, were determined.

Non-destructive monitoring of qualitative properties of salted cabbage using hyperspectral image analysis

The feasibility of using VIS-NIR and SWIR hyperspectral imaging (HSI) to determine the salinity, soluble solids, and water content in salted kimchi cabbages during the salting process was assessed. Hyperspectral images of kimchi cabbages acquired at different salt concentrations and periods of the salting process were developed as prediction and discriminant models for the qualitative properties. Principal component analysis showed that the distribution according to the spectral characteristics of kimchi cabbages could be grouped, and data reduction for optimal model developing was attempted based on the key wavelengths selected in the loading plot. The optimal partial least squares regression models for the prediction of salinity and soluble solids had best performance by achieving R2p values of over 0.86 and 0.90 in the VIS-NIR and SWIR regions, respectively. The accuracy and specificity of the optimal PLS-DA model for salinity level have improved efficiency to over 0.93. Visualization of the spectrum information in each pixel of the hyperspectral image using the PCA model displayed the salinity level in kimchi cabbages under different salting conditions. The prediction models were sufficiently accurate to consider HSI as a useful tool for controlling and optimizing the salting process.

An environmentally-friendly approach to monovalent Cu-doped ZnS: Physicochemical characterization and photocatalytic activity

Certain semiconducting species suffer from the lack of optical activity in the visible region of electromagnetic spectrum, due to large band gap. The integration of various dopants has been widely used in order to generate additional electron transitions and subsequently lead to red-shifted absorption spectrum and enhanced photon harvesting in the visible-NIR region. Herein, a facile two-step environmentally-friendly approach was employed to integrate monovalent Cu species onto ZnS lattice. The study was set to assess the effect of Cu doping in Zinc Sulfide lattice on optical and photocatalytic properties. The theoretical weight fraction of the dopant ranged between 0% and 50%. The physicochemical characterization of either neat semiconductors (ZnS and Cu2O) or Cu-doped ZnS hybrids was performed by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman, X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and Diffuse reflectance spectroscopy (DRS). XPS provided some enhanced understanding about the chemical speciation of the hybrid materials. This information was strongly supported by Raman analysis. The optimized Cu-doped ZnS hybrid demonstrated enhanced photocatalytic activity towards the degradation of Orange G dye, under UV irradiation.

Engineering the surface roughness of the gold nanoparticles for the modulation of LSPR and SERS

In this work, we reported that by using a strong thiol ligand as the morphology-directing reagent, a series of Au nanoparticles with plate-like surface sub-structures could be successfully obtained via a one-pot seedless synthesis. The size and the density of the plates on the surface of Au can be readily tuned with the amount of the thiol ligand, resembling different roughness of the surface. Arising from the different surface roughness, the localized surface plasmon resonance (LSPR) of these shape and morphological alike Au nanoparticles can be continuously tuned within the visible-NIR region. The broad LSPR absorptions and feasible tunability make the Au nanoparticles suitable candidate for plasmonic-related applications. Interestingly, huge SERS enhancement was simultaneously achieved based on the specific surface roughness. Our results demonstrate the great potentials for tuning the LSPR and SERS of Au nanostructures through the engineering of the surface morphologies, which would assist for the design, synthesis, and applications of Au-based plasmonic nanomaterials in various fields.

Formation of skyrmion phase in the Fe–Co–Si system by mechanochemical activation

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mössbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mössbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mössbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mössbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5–300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV–Vis–NIR region of the spectrum was found to increase with BMT.

Heavily Doped Carbon Nitride Nanocrystal Promotes Visible-Near-Infrared Photosynthesis of Hydrogen Peroxide with Near-Unit Photon Utilization.

Direct photosynthesis of hydrogen peroxide (H2O2) from water and oxygen represents an intriguing alternative to the current indirect process involving the reduction and oxidation of quinones. However, limited light utilization and sluggish charge transfer largely impede overall photocatalytic efficiency. Herein, we present a heavily doped carbon nitride (CNKLi) nanocrystal for efficient and selective photoproduction of H2O2 via a two-electron oxygen reduction reaction (ORR) pathway. CNKLi induces metal-to-ligand charge transfer (MLCT) and electron trapping, which broadens the light absorption to the visible-near-infrared (vis-NIR) spectrum and prolongs the photoelectron lifetime to the microsecond time scale with an exceptional charge diffusion length of ∼1200 nm. Near-unit photoutilization with an apparent quantum yield (AQY) of 100% for H2O2 generation is achieved below 420 nm. Impressively, CNKLi exhibits an appreciable AQY of 16% at 700 nm, which reaches the absorption capacity (∼16%), thus suggesting a near-unit photon utilization <700 nm. In situ characterization and theoretical calculations reveal the facilitated charge transfer from K+ to the heptazine ring skeleton. These findings provide an approach to improve the photosynthetic efficiency of direct H2O2 preparation in the vis-NIR region and expand applications for driving kinetically slow and technologically desirable oxidations or high-value chemical generation.

Metal‐Free Organic Dyes for NiO‐Based Dye‐Sensitized Solar Cells: Recent Developments and Future Perspectives

The increasing global demand for energy and growing environmental concerns emphasize the crucial role of solar energy as a sustainable and nondepletable resource. Solar cells, particularly dye‐sensitized solar cells (DSSCs), have gained prominence due to their efficient conversion of solar power, ecofriendly manufacturing processes, and noteworthy stability. Current research in sustainable energy focuses on transitioning from metal‐based to metal‐free organic materials. Tandem solar cells, combining n‐type and p‐type semiconductors sensitized with diverse photoactive dyes, show potential to surpass thermodynamic limits in photon conversion efficiency. Notably, the exploration of n‐type DSSCs as photoanodes in tandem architectures is promising. However, the absence of efficient p‐type photoactive cathodes remains a significant obstacle. Global research efforts are dedicated to addressing charge recombination issues in NiO‐based devices to enhance the efficiency of p‐type DSSCs. The success of any DSSC hinges on the selection of dyes/sensitizers with suitable anchoring groups, wide absorption in the visible–NIR region, and a high extinction coefficient. This article comprehensively reviews advancements in developing highly efficient p‐type sensitizers, emphasizing their pivotal role in unlocking the full potential of tandem solar cells.

Co2+-laddered heterojunction a next-generation solar-photocatalyst: Unusually improved activity for the decomposition of pharmaceuticals, dyes, and microplastics

Novel and versatile photocatalysts that can work under direct sunlight are in high demand especially for mitigating water contamination. Some of the burgeoning pollutants in water are textile dyes, organic molecules, pharmaceutical products etc. In view of their extensive use, polymer wastes such as microplastics in water bodies are a new cause of concern. Using direct sunlight for the degradation of such pollutants needs the development of solar photocatalysts. We report on a novel next-generation solar-photocatalyst, consisting laddered-heterojunction formed between Co2+- substituted zinc-ferrite core & zinc-oxide shell, to harvest full-solar-spectrum in scavenger-free photodegradation of dyes, pharmaceuticals and microplastics. Using in-house developed protocols and Microwave-assisted-solvothermal-technique (MAST), nanospheres of ∼20–40 nm were synthesized first followed by ZnO shell growth in a controlled manner (∼80–180 nm) to obtain the core-shell photocatalyst nanospheres using another microwave approach. The absorption of the photocatalyst could be extended upto 852 nm by judiciously doping with Co2+- enabling the utilization of UV–Vis-NIR region of sunlight. As evident from the valence band spectra, the Co2+ substitution introduced free electrons in the conduction band of ZnFe2O4 that resulted in the formation of laddered type-1 heterojunction. With the optimized Co2+content and ZnO-shell thickness, solar-photocatalytic degradation of Methyl-Orange enhanced 6-&12-times respectively. Complete degradation of antibiotics like Ciprofloxacin (CF), Norfloxacin (NF), and Ofloxacin (OF) under direct sunlight was achieved within an hour. This unusual enhanced activity was attributed to the inclusion of Co2+, conducive band positions leading to higher absorption and reduced recombination. We also showed the degradation of polypropylene microfibers used in face masks to combat the COVID-19 outbreak could also be degraded., indicating their potential to combat microplastic pollution. Our novel photocatalyst holds promise for sunlight-assisted degradation of a wide range of hazardous pollutants.

Interstitial doping of Mn4+ ions: An effective method to optimize the optical properties of TeO2 single crystal

AbstractTeO2 single crystal has drawn much attention in recent years due to its excellent acousto‐optic (AO) performance in the field of spectral imaging and optical processing. The optical properties of TeO2 single crystal are critical for the fabrication of AO devices. To improve the optical properties of the TeO2 single crystal, Mn4+ ions were doped into the TeO2 lattice. Herein, bulk TeO2 single crystal and TeO2:0.02Mn4+ single crystal have been successfully grown by a Bridgman method. Compared with the TeO2 single crystal, a 30% transmittance increase was observed in the TeO2:0.02Mn4+ single crystal. Furthermore, the TeO2:0.02Mn4+ single crystal shows a smaller extinction coefficient (≤0.01) in the Vis–NIR region, indicating less optical loss. The bandgap energy of TeO2:0.02Mn4+ was broadened from 3.360 to 3.635 eV. In addition, TeO2:0.02Mn4+ single crystal exhibits a higher refractive index (about 2.244), which indicates that TeO2:0.02Mn4+ single crystal is a potential medium for high‐efficiency AO devices.

Effect of Pr3+ concentration in luminescence properties & upconversion mechanism of triple doped NaYF4: Yb3+, Er3+, Pr3+

Lanthanide-doped fluoride nanocrystals (NCs) exhibit excellent optical features, including upconversion and downconversion luminescence (UCL and DCL), that can be utilized in a variety of applications. In this study, we have successfully demonstrated the photoluminescence behavior of triple-doped NaYF4: Yb3+, Er3+, Pr3+ NCs in the Vis-NIR region. Herein, highly monodisperse hexagonal phase NaYF4: Yb0.2, Er0.02, Prx nanocrystals in various Pr3+ (x = 0, 0.1, 0.5, and 1 mol %) concentration with ∼22 nm diameter synthesized by thermal decomposition technique. The photoluminescence studies for all samples were performed under 980 nm laser excitation. The luminescence intensity of Er3+ including blue (407 nm), green (520 and 540 nm), red (654 nm), and near-infrared (845 nm and 1530 nm) emissions was significantly quenched and Pr3+ emission intensity at 1290 nm (Pr3+:1G4→3H5) changes irregularly upon doping with Pr3+ ions. Furthermore, we performed the excitation power dependence and decay time analysis to investigate the energy transfer and upconversion mechanisms of samples. These findings indicate that the presence of praseodymium strongly reduces emission intensities due to abundant cross-relaxation channels. In addition, particle size is an efficient factor, shedding light on the influence of Pr3+ on the energy transfer and upconversion mechanisms of the fluorides.

Optoelectronic and Dielectric Properties of Tenorite CuO Thin Films Sprayed at Various Molar Concentrations

The work in hand presents the elaboration of CuO thin films using a home-made spray pyrolysis technique at room atmosphere. The films were synthesized on preheated glass substrate at 450 °C. The source solution molarity was varied from 0.025 to 0.1 mol/L. The films were characterized by employing X-Ray Diffraction technique, UV-Vis-NIR spectrophotometry, Scanning Electron Microscope imagery, Energy Dispersive Spectroscopy, and four-points probe techniques. The X-ray diffraction analysis confirmed that all films are polycrystalline with a preferred orientation along the plane (−111) of the monoclinic crystal structure phase of tenorite (CuO). The SEM images showed a homogeneous and smooth surface. Crystallinity and grain size were improved. The rise of solution concentration induced a reduction of transmittance and reflectance in the visible region. The energy gap, the absorption coefficient, the extinction coefficient, refractive index, dielectric constant (ԑr and ԑi) and loss energy were estimated from transmittance and reflectance data. The gap energy decreases from 2.72 to 2.56 eV. The film deposited for 0.025 mol/L exhibits the highest real part of the dielectric constant (ԑr ~ 17). The film resistivity which is in order of 102 Ω cm decreases with the increase of molar concentration. The estimated dielectric constant indicated that the resulting CuO thin films could be used as dielectric layers for optoelectronic devices working in Vis-NIR region of radiation. Furthermore, the relatively high band gap, high absorption coefficient and high conductivity of the film obtained at 0.075 mol/L, make them good candidates as absorption layers in solar cells applications.