Search Results (101)

White-light-emitting diodes (wLEDs) are central to next-generation lighting technologies, yet their reliance on critical raw materials (CRMs), such as rare-earth elements, raises concerns regarding sustainability and supply security. In this work, we present a simple, low-cost method to produce photoluminescent carbon-based nanostructures—known as oxidative debris (OD)—via alkaline treatment of graphene oxide (GO) using KOH solutions ranging from 0.04 M to 1.78 M. The resulting OD, isolated from the supernatant after acid precipitation, exhibits strong and tunable photoluminescence (PL) across the visible spectrum. Emission peaks shift from blue (~440 nm) to green (~500 nm) and yellow (~565 nm) as a function of treatment conditions, with excitation wavelengths between 300 and 390 nm. Optical, morphological. and compositional analyses were performed using UV-Vis, AFM, FTIR, and Raman spectroscopy, confirming the presence of highly oxidized aromatic domains. The blue-emitting (S2) and green/yellow-emitting (R2) fractions were successfully separated and characterized, demonstrating potential color tuning by adjusting KOH concentration and treatment time. This study highlights the feasibility of reusing GO-derived byproducts as sustainable phosphor alternatives in wLEDs, reducing reliance on CRMs and aligning with green chemistry principles. Full article

Organic violet-blue fluorescent materials have garnered significant interest for a broad spectrum of applications. A series of triazine-based molecules, that is, 2,4,6-tri(9H-carbazol-9-yl)-1,3,5-triazine (TCZT), 2,4,6-tri(1H-indol-1-yl)-1,3,5-triazine (TIDT), and 2,4,6-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,3,5-triazine (TDBCZT), exhibiting violet-blue emission were synthesized via a catalyst-free aromatic nucleophilic substitution reaction. These compounds possess a non-planar and twisted structure with favorable charge-transfer characteristics, demonstrating excellent thermal stability (decomposition temperatures of 370 °C, 384 °C, and 230 °C, respectively). Cyclic voltammetry analysis, combined with time-dependent density functional theory (TD-DFT) calculations at the B3LYP/6-31G(d) level, offered detailed insights into their electronic structures and electrochemical properties. Optical properties were systematically characterized using Ultraviolet–visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy. The compounds exhibited violet-blue luminescence with emission peaks located at 397 nm, 383 nm, and 402 nm in toluene, respectively. In their respective films, the compounds exhibited varying degrees of spectral shifts, with emission peaks at 408 nm, 381 nm, and 369 nm. Moreover, the CIE (Commission Internationale de l’Éclairage) coordinates of TIDT in toluene were (0.155, 0.067), indicative of excellent violet purity. These compounds demonstrated significant two-photon absorption (TPA) properties, with cross-sections of 4.6 GM, 15.3 GM, and 7.4 GM, respectively. Notably, they exhibited large molar absorptivities and substantial photoluminescence quantum yields (PLQYs), suggesting their potential for practical applications as violet-blue fluorescent materials. Full article

Two modifications of ZnMoO₄ were successfully obtained by mechanochemical treatment with two milling speeds applied at 500 and 850 rpm. The phase formation was monitored by XRD analysis. The metastable monoclinic ß-ZnMoO₄ was directly synthesized at room temperature using the higher milling speed of 850 rpm. The thermodynamically stable triclinic α-ZnMoO₄ was obtained by combining heat treatment t 600 °C and ball milling at the lower milling speed of 500 rpm. The IR spectra contain typical vibration bands and confirm the formation of both ZnMoO₄ polymorphs. UV-Vis absorption and photoluminescence (PL) spectroscopy are used to study the optical properties of the as-prepared samples. The calculated optical band gaps for α- and ß-ZnMoO₄ are 4.09 and 3.02 eV. The photoluminescence emission spectrum of both samples shows peaks with different maximum intensity at 615 and 403 nm for α and ß phase, respectively. CIE co-ordinates are located in the orange and blue range of the color diagram. Full article

Nanoparticles of GdAlO₃:Ce were synthesized with sodium dodecylbenzene sulfonate (SDBS) as the dispersant and ammonia as the precipitant by co-precipitation reaction to prepare precursors under different conditions. The phase composition of the precursors and the particle morphology were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The excitation and emission spectra of the resultant samples were analyzed using a photoluminescence spectroscope (PL). The results showed that the as-prepared, well-dispersed, nano-sized GdAlO₃:Ce powder displayed spherical morphology at the initial concentration of metallic salt in liquor of 0.3 mol/L; the synthesized temperature was 0 °C, and it was calcined at 1300 °C for 2 h. The relative intensity of the photoluminescence peak had the maximum value when the Ce³⁺ dopant content was 0.9 mol% (mole fraction). The concentration quench occurred when the Ce³⁺ dopant content exceeded 0.9 mol%, and the peak of the excitation spectrum appeared at a wavelength of 381 nm. Full article

We elaborate a method for determining the 0D–1D nanostructure size by photoluminescence (PL) emission spectrum dependence on the nanostructure dimensions. As observed, the high number of diamond-like carbon nanocones shows a strongly blue-shifted PL spectrum compared to the bulk material, allowing for the calculation of their top dimensions of 2.0 nm. For the second structure model, we used a sharp atomic force microscope (AFM) tip, which showed green emission localized on its top, as determined by confocal microscopy. Using the PL spectrum, the calculation allowed us to determine the tip size of 1.5 nm, which correlated well with the SEM measurements. The time-resolved PL measurements shed light on the recombination process, providing stretched-exponent decay with a τ₀ = 1 ns lifetime, indicating a gradual decrease in exciton lifetime along the height of the cone from the base to the top due to surface and radiative recombination. Therefore, the proposed method provides a simple optical procedure for determining an AFM tip or other nanocone structure sharpness without the need for sample preparation and special expensive equipment. Full article

China is the country with the most abundant bamboo resources in the world. Using bamboo as a raw material for pulping and papermaking can save a lot of wood and protect forests. Bamboo pulping enterprises mostly adopt sulfate processes to produce a large amount of black liquor (BL), which contains monosaccharides, polysaccharides, oligosaccharides, pectin, lignin, etc. The utilization of the high-value organic matter is of great economic and environmental significance. In this study, blue-green carbon dots (C-dots) were prepared from bamboo (Lingnania chungii) kraft pulp BL using a hydrothermal method. The changes in carbohydrate content in BL in relation to hydrothermal temperature and hydrothermal time were discussed in detail. Then, a series of characterizations of BL-C-dots, prepared under one of the hydrothermal conditions (180 °C, 6 h), were performed and the BL-C-dots showed an excitation-dependent photoluminescence (PL) spectrum and a quantum yield (QY) of 2.9% in an aqueous solution. Finally, the as-prepared BL-C-dots were successfully used as fluorescent materials to develop an anti-counterfeiting code. The fluorescent code exhibited a clear outline, an excitation-tunable color, good stability, and high security, showing great anti-counterfeiting potential and realizing the high-value utilization of BL. Full article

Multicolor emission and dynamic color tuning with large spectral range are challenging to realize but critically important in many areas of technology and daily life, such as general lighting, display, multicolor detection and multi-band communication. Herein, we report an excitation-power-dependent color-tuning emission from an individual Sn-doped CdS nanowire with a large spectral range and continuous color tuning. Its photoluminescence (PL) spectrum shows a broad trap-state emission band out of Sn dopants, which is superposed by whispering-gallery (WG) microcavity due to the nanostructure size and its structure, besides the CdS band-edge emission. By simply changing the excitation power from 0.25 to 1.36 mW, we demonstrate that the typical Sn-doped CdS nanowire with the weight ratio of 10:1 of CdS and SnO₂, the emission color can change from red to orange to yellow to green. In view of the stable properties and large spectral range, the Sn-doped CdS nanowires are very promising potential candidates in nanoscale optoelectronic devices. Full article

A new scintillation material composed of InAs quantum dots (QDs) hosted within a GaAs matrix was developed, and its performance with different types of radiation is evaluated. A methodology for designing an integrated photodetector (PD) with a low defect density and that is optically matched to the QD’s emission spectrum is introduced, utilizing an engineered epitaxial InAlGaAs metamorphic buffer layer. The photoluminescence (PL) collection efficiency of the integrated PD is examined using two-dimensional scanning laser excitation. The detector response to 5.5 MeV α-particles and 122 keV photons is presented. Yields of 13 electrons/keV for α-particles and 30–60 electrons/keV for photons were observed. The energy resolution of 12% observed with α-particles was mainly limited by noise- and geometry-related optical losses. The radiation hardness of an InAs QDs hosted within GaAs and a wider band gap AlGaAs ternary alloy was studied under a 1 MeV proton implantation up to a 10¹⁴ cm⁻² dose. The integrated PL responses were compared to evaluate PL quenching due to non-radiative defects. The QDs embedded in the AlGaAs demonstrated improved radiation hardness compared to QDs in the GaAs matrix and in the InGaAs quantum wells. Full article

The large-scale utilization of antibiotics has opened a separate chapter of pollution with the generation of reactive drug-resistant bacteria. To deal with this, in this work, different mass ratios of CoFe₂O₄/WO₃ nanocomposites were prepared following an in situ growth method using the precursors of WO₃ and CoFe₂O₄. The structure, morphology, and optical properties of the nanocomposite photocatalysts were scrutinized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectra (UV-Vis DRS), photoluminescence spectrum (PL), etc. The experimental data signified that the loading of CoFe₂O₄ obviously changed the optical properties of WO₃. The photocatalytic performance of CoFe₂O₄/WO₃ composites was investigated by considering tetracycline as a potential pollutant. The outcome of the analyzed data exposed that the CoFe₂O₄/WO₃ composite with a mass ratio of 5% had the best degradation performance for tetracycline eradication under the solar light, and a degradation efficiency of 77% was achieved in 20 min. The monitored degradation efficiency of the optimized photocatalyst was 45% higher compared with the degradation efficiency of 32% for pure WO₃. Capturing experiments and tests revealed that hydroxyl radical (·OH) and hole (h⁺) were the primary eradicators of the target pollutant. This study demonstrates that a proper mass of CoFe₂O₄ can significantly push WO₃ for enhanced eradication of waterborne pollutants. Full article

In recent years, many studies have been published on CVD diamond growth, but the reason for the irregular blue surface fluorescence of CVD diamond under ultra-deep UV radiation (i.e., under DiamondView) is still unclear. Here, a batch of as-grown and LPHT-annealed CVD synthetic diamond samples from a Chinese company in Zhejiang were analyzed for the various spectral (infrared (IR), UV–visible absorption, Raman, and photoluminescence (PL)) characteristics to explore the origin of surface blue fluorescence. The results show that the samples are nitrogen-doped type IIa CVD synthetic diamonds. Spectral peaks of the earlier CVD products, e.g., 3123 cm⁻¹ (NVH⁰) (IR absorption spectrum) and 596/597 nm (PL emission spectrum), are absent in these samples, while the peaks at 736.5/736.8 nm (SiV⁻) in the UV or PL spectra are less common. PL spectra and DiamondView fluorescence indicate that the samples have generally strong luminescence peaks at 637 nm in the NV⁻ center, 575 nm in the NV⁰ center, and other luminescence peaks caused by nitrogen-related defects. The as-grown samples observed under DiamondView show orange-red fluorescence accompanied by striations due to step-flow growth, and blue fluorescence appears as irregular threads or bundles on the surface. The LPHT-annealed sample shows weaker fluorescence with localized patches of green fluorescence contributed by weak H3 centers. The micro-IR spectra suggest that the unique blue fluorescence in the CVD diamond may be related to the dislocations caused by sp³-CH₂ due to the incomplete dehydrogenation of hydrocarbon groups in the raw material. Full article

A room-temperature photoluminescence (PL) study of amorphous Si/amorphous silicon oxynitride multilayer films prepared by plasma-enhanced chemical vapor deposition is reported. The PL peak position can be tuned from 800 nm to 660 nm by adjusting the oxygen/nitride ratio in the a-SiO_xN_y:H sublayer. The Fourier transform infrared (FTIR) absorption spectra indicate that the shift of the PL peak position is accompanied by an increase in the Si-O-Si absorption peak’s intensity, which induces the structural disorder at the interface, resulting in an increase in band gap energy. The effects of size on the photoluminescence spectrum have been studied. As a result, it has been observed that the addition of oxygen atoms introduces a large number of localized states at the interface, causing a blue shift in the emission peak position. With an increase in oxygen atoms, the localized states tend to saturate, and the quantum phenomenon caused by the a-Si sublayer becomes more pronounced. It is found that, as the thickness of the a-Si sublayer decreases, the increase in the [O/N] ratio is more likely to cause an increase in disordered states, leading to a decrease in luminescence intensity. For a-Si/a-SiO_xN_y:H samples with thinner a-Si sublayers, an appropriate value of [O/N] is required to achieve luminescence enhancement. When the value of [O/N] is one, the enhanced luminescence is obtained. It is also suggested that the PL originates from the radiative recombination in the localized states’ T_3- level-related negatively charged silicon dangling bond in the band tail of the a-Si:H sublayer embedded in an a-Si/a-SiO_xN_y:H multilayer structure. Full article

High-temperature and high-pressure (HTHP)-treated diamonds have attracted attention all over the world due to their vivid colors. In order to explore a new method for the rapid and non-destructive identification of HTHP-treated diamonds, in this paper, five IaAB-type diamonds yielded in Russia were selected as the research object and treated with HTHP. The HTHP-treated diamonds were investigated by DiamondView^TM, cathodoluminescence, micro-infrared spectrometry (micro-IR), low-temperature photoluminescence (PL) spectrometry, and three-dimensional (3D) fluorescence spectrometry. The results show that under DiamondView^TM and cathode rays, the five samples were all non-phosphorescent with different luminous patterns, such as regular annular bands, multiple groups of intersecting linear stripes, or jagged stripes. In the low-temperature PL spectra, most HTHP-treated diamonds exhibited stronger luminescence peaks at 637 nm compared to 575 nm. But there were also exceptions, such as the purple-red sample showing the opposite luminescence peak. In the 3D fluorescence spectrum of the HTHP-treated diamonds, the fluorescence peak mainly appeared in the range of 440–450 nm, accompanied by a broad band of 350–500 nm and even longer wavelengths. Meanwhile, some samples also exhibited fluorescence peaks at longer wavelengths, such as 353 nm, 676 nm, and 665 nm. These results make it possible to identify HTHP-treated diamonds by using luminescence characteristics, providing a new method for the non-destructive and rapid detection of HTHP-treated diamonds. Full article

This study introduces an innovative method for synthesizing Cadmium Oxide /Cadmium Sulfide/Zinc Oxide heterostructures (CdO/CdS/ZnO), emphasizing their potential application in solar energy. Utilizing a combination of electrochemical deposition and oxygen annealing, the research provides a thorough analysis of the heterostructures through scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) spectroscopy. The findings reveal a complex surface morphology and a composite structure with significant contributions from hexagonal CdS and cubic CdO phases. The study highlights the uniformity in the distribution of luminescent centers and the crystalline quality of the heterostructures, which is evident from the PL analysis. The redshift observed in the emission peak and the additional peaks in the excitation spectrum indicate intricate optical properties influenced by various factors, including quantum confinement and lattice strain. The research demonstrates these heterostructures’ potential in enhancing solar cells’ efficiency and applicability in optoelectronic devices. This comprehensive characterization and analysis pave the way for future optimization and application in efficient and sustainable solar energy solutions. Full article

MgAl oxide coatings composed of MgO and MgAl₂O₄ phases were doped with CeO₂ particles via plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy in a 5 g/L NaAlO₂ water solution. Subsequently, particles of CeO₂ up to 8 g/L were added. Extensive investigations were conducted to examine the morphology, the chemical and phase compositions, and, most importantly, the photoluminescent (PL) properties and photocatalytic activity (PA) during the photodegradation of methyl orange. The number of CeO₂ particles incorporated into MgAl oxide coatings depends on the concentration of CeO₂ particles in the aluminate electrolyte. However, the CeO₂ particles do not significantly affect the thickness, phase structure, or surface morphology of the coatings. The PL emission spectrum of MgAl oxide coatings is divided into two bands: one in the 350–600 nm range related to structural defects in MgO, and another much more intense band in the 600–775 nm range attributed to the F⁺ centres in MgAl₂O₄. The incorporated CeO₂ particles do not have a significant effect on the PL intensity of the band in the red spectral region, but the PL intensity of the first band increases with the concentration of CeO₂ particles. The PA of MgAl/CeO₂ oxide coatings is higher than that of pure MgAl oxide coatings. The MgAl/CeO₂ oxide coating developed in aluminate electrolyte with a concentration of 2 g/L CeO₂ particles exhibited the highest PA. The MgAl/CeO₂ oxide coatings remained chemically and physically stable across multiple cycles, indicating their potential for applications. Full article

This work studies the technological preparation conditions, morphology, structural characteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped β–Ga₂O₃ nanoformations on ε–GaSe:Eu single crystal substrate, obtained by heat treatment at 750–900 °C, with a duration from 30 min to 12 h, in water vapor-enriched atmosphere, of GaSe plates doped with 0.02–3.00 at. % Eu. The defects on the (0001) surface of GaSe:Eu plates serve as nucleation centers of β–Ga₂O₃:Eu crystallites. For 0.02 at. % Eu doping, the fundamental absorption edge of GaSe:Eu crystals at room temperature is formed by n = 1 direct excitons, while at 3.00 at. % doping, Eu completely shields the electron–hole bonds. The band gap of nanostructured β–Ga₂O₃:Eu layer, determined from diffuse reflectance spectra, depends on the dopant concentration and ranges from 4.64 eV to 4.87 eV, for 3.00 and 0.05 at. % doping, respectively. At 0.02 at. % doping level, the PL spectrum of ε–GaSe:Eu single crystals consists of the n = 1 exciton band, together with the impurity band with a maximum intensity at 800 nm. Fabry–Perrot cavities with a width of 9.3 μm are formed in these single crystals, which determine the interference structure of the impurity PL band. At 1.00–3.00 at. % Eu concentrations, the PL spectra of GaSe:Eu single crystals and β–Ga₂O₃:Eu nanowire/nanolamellae layers are determined by electronic transitions of Eu²⁺ and Eu³⁺ ions. Full article