UV Excitation Research Articles

Optical properties of carbon dots generated in liquid by pulsed IR laser at 1064 nm

Biocompatible carbon dots (CDs) have been synthesized by the laser ablation of graphite and vegetable carbon (charcoal) placed in a phosphate-buffered saline (PBS) solution. The carbon nanoparticles are produced by a pulsed IR laser beam, operating at 1064 nm, 100 mJ energy, and 3 ns pulse duration, interacting with the carbon matrix placed in the liquid at a 0.2 Hz repetition rate. The ablation rate, in terms of removed carbon mass per laser shot, was evaluated to be about 75.8 ng/pulse and 758 ng/pulse for graphite and charcoal, respectively. Optical and electronic microscopy, UV-Vis spectroscopy, and luminescence measurements were employed to evince the CDs dispersion through its photoluminescence emission. The UV excitation at a 365 nm wavelength induces CDs luminescence in the visible region, as a result of electron transition, at a wavelength band depending on the laser spot size, i.e., of the laser fluence. CDs luminescence emission obtained from charcoal is independent of the laser fluence, showing a major emission peak around 475 nm and a secondary emission peak at 515 nm. CDs luminescence emission obtained from graphite depends on the laser fluence, showing a minor wavelength band, around 474 nm, at high laser fluences and a major wavelength band, around 670 nm, at low laser fluence. The CDs luminescence of the produced biocompatible solution finds many applications in the bio-medical field, as will be presented and discussed.

Non-invasive methods to assess seed quality based on ultra-weak photon emission and delayed luminescence.

Seed quality is the set of physical, genetic, and physiological characteristics, reflecting the overall germination potential. Maintaining an optimal seed quality is essential for agriculture and seed banks to preserve genetic diversity. Compared to conventional methods (e.g., germination tests), non-invasive approaches allow a more sustainable and rapid evaluation of seed quality but this is limited by high costs. The measurement of ultra-weak photon emission (UPE) and delayed fluorescence (DL), defined as biological phenomena potentially related to the physiological status of living systems, may represent a suitable approach to estimate seed quality. To test this hypothesis, seeds of five agriculturally relevant legume species (Phaseolus vulgaris L., Lathyrus sativus L., Cicer arietinum L., Pisum sativum L., and Vicia faba L.), stored at different conditions (room temperature or -18°C) for several years, were analysed using a LIANA© prototype to collect data regarding DL and UPE occurring after UV excitation. The obtained data were integrated with germination parameters which underline species-specific behaviours in response to storage conditions. The prediction models show variable efficiency in classifying seeds based on germination which underline species-dependent links between photon emission and seed quality. Therefore, these measurements represent novel, non-invasive, and rapid approaches to evaluate seed quality.

Room temperature n-butanol detection by Ag-modified In2O3 gas sensor with UV excitation

The aim of this study is to develop a sensor for the detection of n-butanol gas at room temperature, which in turn facilitates sensor integration. To this end, porous In2O3 nanosheets were prepared in this experiment, along with noble metal Ag modification and UV excitation, to achieve effective monitoring of low concentrations of n-butanol at room temperature. The material composition and structure were analyzed by various analysis techniques. The addition of precious metals promotes the absorption of UV light by the material. The n-butanol gas sensitivity test was completed on individual samples under 365 nm UV. The response of 5wt% Ag/In2O3 to 10 ppm n-butanol under UV irradiation reaches 127.5% at room temperature, which is twice as much as pure In2O3. The sensor showed a well regular answer at different concentrations of n-butanol. This paper also discusses the sensing mechanism for the improved gas-sensitive behavior of Ag/In2O3, which mainly benefits from the chemical and electron sensitizing of Ag. The results show that the Ag/In2O3 material excited by ultraviolet light in this paper lays a certain foundation for the preparation of room temperature n-butanol gas sensor.

Temperature Dependent Photoluminescence Properties of a Y2Ge2O7:Tb3+ phosphors. A dual band ratiometric luminescent thermometer

A series of green light emitting Y2Ge2O7:xTb3+ phosphors (x = 0.2, 0.5, 1.0, 2.0 and 4.0mol%) were obtained via the solid-state reaction method. The single phase was confirmed by XRD technique. The photoluminescence (PL) excitation spectrum, emission spectra at room and as a function of temperature, decay curves of phosphors were studied in detail. The emission spectra show typical emissions of Tb3+ ions, whose relative intensities change with the ion concentration or UV excitation. A shift of the CIE chromaticity coordinates from blueish to green region was observed. The emission decay curves are compatible with a single type of Tb3+ activator. The obtained internal Quantum Yield (iQY) increase with the terbium concentration, up to 10.0% for sample with 4.0mol%. In addition, the relative sensitivity values (Sr) for samples with 1.0 and 2.0mol% reached 0.97 and 2.02%K-1, respectively. These high thermal sensitivities obtained, in comparison with other Tb3+ based optical temperature sensors, in biophysical temperature range (30–45 °C), illustrates the potential use of Y2Ge2O7:xTb3+ phosphors in the design of efficient FIR luminescent thermometers for biological systems or other industrial applications.

Triple-Mode Protection with Ln3+ Ion-Doped Core-Heptad-Shell Single Nanocrystals for High-Level Security Applications.

In this work, oleic acid (OA)-capped core-heptad-shell (CHS) nanocrystals (NCs) that exhibit multiple emissions achieved through downshifting and orthogonal upconversion are synthesized via layer-by-layer thermal decomposition. This method enables the downshifting process to be accommodated by doping ions in the inert space between two upconversion patterns (the core and fourth shell) and doping Ce/Tb or Ce/Eu ions in the NaGdF4 layer for the first time. These developed CHS NCs exhibit different emission colors via 980 and 800 nm orthogonal upconversion and downshifting emissions under 256 nm UV excitation in hexane solvent. Furthermore, surface-functionalized OA is removed using mild acid treatment. The resulting bare CHS NCs disperse well in water and exhibit 21.60-fold and 43.59-fold higher Ce/Tb and Ce/Eu luminescence intensities, respectively, than the OA-capped CHS NCs. These NCs are mixed with a carboxymethylcellulose (CMC) polymer in an aqueous medium to form a CMC-CHS NC gel. Invisible patterns and QR codes are printed on nonfluorescent paper using gels and screen-printing techniques. These patterns and QR codes exhibit three different emission colors under three different excitations. This method can be used for high-level anticounterfeiting applications.

Optical Characteristics of the Black Seed Oil: Fluorescence and Adulteration Detection.

Understanding the optical characteristics, especially the fluorescence properties of vegetable oils, particularly black seed oil (BSO), is an essential prerequisite for the development of the future applications in both medicinal and nutritional fields. In this way, it is essential to identify the roles played by the components such as unsaturated fatty acids, carotenoids, flavonoids, vitamin E, and chlorophylls in the BSO fluorescence spectra. In the current landscape, challenges arise from the adulteration of BSO with impurities such as sunflower oil (SO), complicating efforts to obtain pure BSO. Here, dependence of the BSO fluorescence on excitation wavelength has been examined using UV- visible diode lasers (λ = 355, 405, 440, 532 and 660nm) as excitation sources. Though conjugated unsaturated fatty acids, flavonoids and chlorophylls are mainly contributed to the fluorescence due to UV excitation, wavelengths in the visible range specifically excite carotenoids, vitamin E, and chlorophylls. By utilizing the laser-induced fluorescence (LIF) technique, we explored the effects of inner filters and setup geometry to gain deeper insights into the BSO fluorescence dynamics. Differential spectral analysis (DSA) revealed that adulteration of BSO with SO alters its fluorescence features. As a result, a novel approach is proposed for adulteration detection, based on the simultaneous excitation of BSO and SO by a 405nm laser, benefit to indirect excitation of the carotenoids of BSO by fluorescence emission of SO within the spectral range of 400-500nm, which results in the enhancement of BSO fluorescence in the region of 500-600nm.

Gan Photonic Crystals: Spectral Dynamics in UV, X‐Ray, and Alpha Radiation

In this work, a comparative analysis of gallium nitride (GaN) thin films is conducted, both with and without photonic crystal (PhC) structures, focusing on their scintillation and photoluminescence properties. GaN's suitability for diverse optoelectronic and radiation detection applications is analyzed, and this study examines how PhC implementation can enhance these properties. Methodologically, the emission spectra is analyzed from 5.9 keV X‐ray sources, decay curves, pulse height spectra in response to 241Am 5.5 MeV alpha‐rays, and photoluminescence spectra induced by UV excitation. The findings demonstrate a substantial increase in quantum efficiency for PhC GaN, nearly tripling the light yield that of conventional plain GaN thin films under the UV excitation. The enhancement is predominantly attributed to the PhC GaN's proficiency in guiding light at 550 nm, a feature indicative of its spectral filtering capabilities, as detailed in the study. Furthermore, side‐band scintillations, stemming from inherent materials like Chromium that generate scintillations at diverse wavelengths, are effectively mitigated. A key finding of this study is the effective detection of light not only at the rear but also along the lateral sides of the films, offering new possibilities for radiation detector design and architecture.

Reactive spark plasma sintering and luminescence properties of Gd2O2S:Tb nanocrystalline phosphor

Gd2O2S:Tb is promising for energy-efficient lighting and display applications. This work explores the use of reactive spark plasma sintering (SPS) to synthesis Gd2O2S:Tb nanocrystalline phosphor. It allows to significantly simplify the technological process in comparison with traditional multi-stage liquid-phase synthesis. As-sintered Gd2O2S:Tb demonstrated average crystallite size of 26 nm and secondary particle size of 26 μm. Bright green emission occurs at 545 nm under UV excitation of 245 nm. Average fluorescence lifetime was 0.656 ms. Further consolidation of the Gd2O2S:Tb prepared via reactive SPS can also be expected to yield highly dense ceramics. The innovative reactive synthesis strategies provide valuable insights into the design and development of high-performance luminescent ceramics.

Rare earth element assessment in Jezero crater using the Planetary Instrument for X-ray Lithochemistry on the Mars 2020 rover Perseverance: A case study of cerium

The “Planetary Instrument for X-ray Lithochemistry” (PIXL) X-ray spectrometer conducts in situ geochemical analyses of martian rocks and regolith interrogated by the Mars 2020 rover, Perseverance. In addition to quantifying primary rock-forming elements, PIXL can quantify trace elements that in turn can provide additional constraints on the geologic history of Mars. Accurate quantifications of trace elements can require additional analytical techniques to mitigate experimental, background, and crystalline effects within PIXL spectra. In this study, we focus on reducing the impact of these effects and investigate the potential presence of rare earth elements (REEs). The study specifically investigates cerium given its typical relative abundance in many geologic materials compared to other REEs and its potential to mimic fluorescence features produced by organics under deep UV excitation. A detailed analysis of PIXL targets analyzed through the first 887 martian days of the Perseverance mission did not produce any conclusive Ce detections. Phosphorus-enriched materials analyzed by PIXL are estimated to contain sub-675 ppm Ce and sulfate-enriched materials sub-450 ppm Ce. The method presented can help constrain limits on the abundance of additional trace elements of interest that also face a similar analytical burden. PIXL's potential to assess REE abundances, outside of yttrium, is limited for expected concentrations in surface materials. Determining most REE concentrations in materials interrogated by Perseverance will therefore likely require terrestrial analyses.

Flexible X-ray Imaging and Stable Information Storage of SrF2:Eu Based on Radio-Photoluminescence.

X-ray imaging has garnered widespread interest in biomedical diagnosis and nondestructive detection. The exploration of radio-photoluminescence has hastened the advancement of X-ray information storage. However, significant challenges persist in achieving the prolonged imaging of curved objects without attenuation. Here, europium-doped strontium fluoride (SrF2:Eu) is meticulously created to exhibit a linear response to an extensive range of X-ray doses (maximum dose > 5000 Gy), showcasing excellent X-ray information reading/erasing reusability properties (10 cycles). This is accompanied by a red-to-blue emission transition under UV excitation, sustaining for 150 days without attenuation. To elucidate the phenomena of irradiated photoluminescent discoloration and the reversible X-ray storage of SrF2:Eu, we propose an electron-vacancy trap (valence conversion) mechanism, information stably retained by the SrF2:Eu-based device under ambient conditions due to high energy barriers. The time-lapse readout capability is further demonstrated for three-dimensional imaging of curved objects (10 lp mm-1) based on SrF2:Eu embedded within a polydimethylsiloxane (SrF2:Eu@PDMS). The SrF2:Eu demonstrates time-lapse imaging, reversible radio-photoluminescence, and recoverable X-ray storage, offering a promising avenue for optical information encryption and anticounterfeiting applications.

Cationic or Neutral: Dependence of Photophysical Properties of Bis-Alkynylphosphonium Pt(II) Complexes on Ancillary Ligand.

A series of D-π-A alkynylphosphonium salts with different linker between donor and acceptor groups was used to synthesize two series of trans-bis-alkynylphosphonium Pt(II) complexes with different ancillary ligands (triphenylphosphine, P series, and cyanide, CN series). The nature of the ancillary ligand manages the overall charge and emission properties of the complexes obtained. In addition, the variation of the linker in alkynylphosphonium ligands allows fine-tuning the luminescence wavelength. Dicationic series P is unstable in solution under UV excitation, whereas in the solid state, these complexes are the first example of phosphorescent trans-phosphine-bis-alkynyl Pt(II) compounds. Neutral series CN demonstrates bright emission in solution, including dual emission for 2CN complex with biphenyl linker in alkynylphosphonium ligand. However, in the solid state for the CN series drastic decrease in the emission quantum yield compared to the P series was observed. DFT calculations reveal the complicated emission nature for the both P and CN series with various contributions of 3ILCT, 3LLCT and 3MLCT states. However, in the naphthyl-containing derivatives 3P and 3CN, the dominating 3LC character with some admixture of CT states is postulated.

Achieving Efficient X-ray Scintillation of Purely Organic Phosphorescent Materials by Chromophore Confinement.

Scintillators have attracted significant attention due to their wide-ranging applications in both industrial and medical fields. However, one of the ongoing challenges is the efficient utilization of triplet excitons to achieve high radioluminescence efficiency. Here, a series of purely organic phosphors is presented for X-ray scintillation, employing a combined rigid and flexible host-guest doping strategy. The doped crystals exhibit a remarkable maximum phosphorescence efficiency of 99.4% under UV excitation. Furthermore, upon X-ray irradiation, the radioluminescence intensities of the doped phosphors are markedly higher compared to their single-component crystal counterparts. Through systematic investigations, it is demonstrated the crucial role of confining isolated chromophores in enhancing scintillation efficiency. Additionally, a transparent scintillator screen fabricated with the doped phosphor exhibits excellent X-ray imaging performance, achieving a high spatial resolution of 18.0 lpmm-1. This work not only offers valuable insights into suppressing non-radiative transitions of triplet excitons during scintillation but also opens a new avenue for designing highly efficient purely organic phosphorescent scintillators.

UV-Induced Reaction Pathways in Bromoform Probed with Ultrafast Electron Diffraction.

For many chemical reactions, it remains notoriously difficult to predict and experimentally determine the rates and branching ratios between different reaction channels. This is particularly the case for reactions involving short-lived intermediates, whose observation requires ultrafast methods. The UV photochemistry of bromoform (CHBr3) is among the most intensely studied photoreactions. Yet, a detailed understanding of the chemical pathways leading to the production of atomic Br and molecular Br2 fragments has proven challenging. In particular, the role of isomerization and/or roaming and their competition with direct C-Br bond scission has been a matter of continued debate. Here, gas-phase ultrafast megaelectronvolt electron diffraction (MeV-UED) is used to directly study structural dynamics in bromoform after single 267 nm photon excitation with femtosecond temporal resolution. The results show unambiguously that isomerization contributes significantly to the early stages of the UV photochemistry of bromoform. In addition to direct C-Br bond breaking within <200 fs, formation of iso-CHBr3 (Br-CH-Br-Br) is observed on the same time scale and with an isomer lifetime of >1.1 ps. The branching ratio between direct dissociation and isomerization is determined to be 0.4 ± 0.2:0.6 ± 0.2, i.e., approximately 60% of molecules undergo isomerization within the first few hundred femtoseconds after UV excitation. The structure and time of formation of iso-CHBr3 compare favorably with the results of an ab initio molecular dynamics simulation. The lifetime and interatomic distances of the isomer are consistent with the involvement of a roaming reaction mechanism.

Cutting-edge applications of oleic acid-modified CdSiO3: Ce3+ phosphors: Artificial intelligence enhanced latent fingerprint detection, anti-counterfeiting and optical thermometry

A series of (1–11 mol%) Ce³⁺ doped CdSiO₃ phosphors are synthesized via a solution combustion method, and the sample with the optimal doping concentration underwent surface modification with oleic acid (OA). X-ray diffraction (XRD) analysis confirmed the formation of high-purity, well-crystallized CdSiO3:Ce3+ phosphors. Upon 347 nm UV excitation, the phosphor exhibited intense blue emission at 400 nm, with an optimized Ce³⁺ concentration of 5 mol%, attributed to dipole-dipole interactions. The OA-modified phosphor demonstrated significantly enhanced properties, achieving a color purity (CP) of 97.2% and Internal quantum efficiency (IQE) of 82.5%. The phosphor also exhibited excellent thermal stability, retaining 93.0% of its emission intensity at 423 K and a thermal quenching temperature exceeding 483 K, with a high activation energy (Eₐ) of 0.384 eV. In practical applications, the OA modified phosphor showed exceptional performance in latent fingerprints (LFPs) detection and anti-counterfeiting (AC) across different substrates, offering high resolution, contrast, and minimal background interference. MATLAB based analysis yielded a matching score of 94.52%, surpassing conventional benchmarks, underscoring the phosphor's potential for advanced fingerprint identification. These results demonstrate that the CdSiO₃:5Ce³⁺ phosphor is a promising candidate for applications in white light-emitting diodes (w-LEDs), optical thermometry, forensic analysis and AC technologies.

Harnessing hetero-atom doped CQDs from Pyrostegia venusta for latent fingerprint and anti-counterfeit applications

The development of innovative techniques for latent fingerprint (LFP) analysis and anti-counterfeiting applications is crucial for addressing various societal challenges. Quantum dot (QD)-based fluorescent staining offers a promising approach due to its high sensitivity. However, the toxicity of traditional heavy metal-containing QDs necessitates the exploration of eco-friendly alternatives. This study presents a facile and environmentally sustainable method for synthesizing heteroatom (nitrogen, phosphorus, and potassium)-doped carbon quantum dots (N-P-K@CQDs) derived from the flower extract of Pyrostegia venusta. Characterization revealed spherical CQDs with an average size of approximately 4.7 nm, a quantum yield of 25 %, and excellent water solubility, photostability, and greenish-fluorescent properties. N-P-K@CQDs were incorporated into a cornstarch nanocomposite phosphor, which exhibited greenish fluorescence under UV excitation. The nanocomposite was utilized as a fluorescent marker for LFP analysis using a customized smartphone-based dactyloscope. Python-based image processing algorithms were employed to enhance and analyze the fluorescence images of the developed LFPs. Additionally; a proof-of-concept anti-counterfeiting tag was demonstrated using CQDs-based ink, enabling the detection of concealed security marks. The findings highlight the potential of eco-friendly N-P-K@CQDs as a versatile platform for both LFP analysis and anti-counterfeiting applications.

Förster Resonance Energy Transfer and Enhanced Emission in Cs4PbBr6 Nanocrystals Encapsulated in Silicon Nano-Sheets for Perovskite Light Emitting Diode Applications.

Encapsulating Cs4PbBr6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs4PbBr6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs4PbBr6 pseudo-spherical quantum dots is quenched and is dominated with Pb2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs4PbBr6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs4PbBr6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials.

From mixed brookite/anatase TiO2 nanopowder to sodium titanates: Insight into morphology, structure, and photocatalytic performance

A method to obtain sodium titanate nanoribbons starting from a mixture of brookite and anatase TiO₂ nanopowder is described. As-prepared TiO2 nanopowder with a major brookite phase was used as a precursor in an alkaline hydrothermal approach, where the temperature was kept at 200 °C. The influence of hydrothermal treatment and consequent annealing temperature (T = 500 °C) on the crystal structure, phase composition, and morphology of samples were investigated by X-ray powder diffraction (XRPD), Raman and FTIR spectroscopy, and electron microscopy techniques (FESEM, HRTEM). All these methods point out that the hydrothermally treated sample, containing the NaTi3O6(OH)(H2O)2, Na2Ti3O7, and Na2Ti9O19, is dominated by layer-structured sodium hydroxititanate dihydrate. The annealing leads to the formation of rare sodium titanates, Na3Ti6O13 and Na2Ti9O19, with tunnel structures where the hexatitanate with increased sodium content prevails. The photocatalytic activity of synthesized nanostructures was tested in the degradation process of Reactive Orange (RO16) azo-dye upon UV excitation. It appears that photocatalytic activity is lower after hydrothermal treatment, but subsequent annealing makes sodium titanate nanoribbons faster in the degradation of RO16. The research implies that these sodium titanate nanostructures are promising photocatalytic materials and should be considered in the future for removing different pollutants from water.

Leveraging photosensitive and thermally stable luminescent Ba2ZnWO6:Eu3+, M+ (M+= Na, K , and Li) nanophosphor for targeted non-invasive and stain-free visualization of cracked tooth syndrome

The cracked tooth syndrome poses a significant challenge in dentistry, thereafter untreated cases often lead to severe complications, such as pulpitis or complete tooth fracture, ultimately contributing to tooth loss. However, the conventional diagnostic methods to visualize microcracks in the tooth suffer from severe drawbacks, such as inaccurate cold stimulation, discomfort with probing, impractical staining techniques, and difficulty in distinguishing harmless craze lines from pathological cracks. To address this challenge, for the first time, we are proposing a novel approach by utilizing luminescent Ba2ZnWO6:Eu3+ (3 mol %), K+ (1 wt %) nanophosphor for improved imaging and diagnosis of cracked tooth syndrome. Herein, the double perovskite structured Ba2ZnWO6:Eu3+ (1–11 mol %), M+ (M+ = Na, K, and Li (1 wt %)) nanophosphors were synthesized via the sonochemical route. The photoluminescence emission spectra of the prepared Ba2ZnWO6:Eu3+ (1–11 mol %) nanophosphors displaying distinct peaks at 583, 595, 613, 662, and 720 nm, which ascribed to transitions from state 5D0 to 7FJ (J = 1–4) state of the Eu3+ ions, respectively. By adopting a strategic charge compensation mechanism, the enhancement in the luminescence emission intensity of about 1.5-fold was achieved after co-doping K+ (1 wt %) with Ba2ZnWO6:Eu3+ (3 mol %) nanophosphor. The photometric studies of the phosphors portray their orange-red emission with excellent quantum efficiency (82.52 %), and color purity (∼ 99 %). The emission intensity was sustained up to 73.71 % at 473 K, indicating excellent thermal stability of the phosphor. The in vitro cytotoxicity assessments of the optimized nanophosphor demonstrated its biocompatibility on normal non-malignant oral fibroblasts. The visualized microcracks in the tooth using optimized Ba2ZnWO6:Eu3+ (3 mol %), K+ (1 wt %) nanophosphor under UV excitation of UV 365 and 395 nm light revealed the orientation of microcracks, crack width, depth of the crack, and microcrack branching without any stain. The aforementioned results demonstrated that the proposed methodology paves the way for a new avenue in dental imaging technology with the potential to revolutionize and improve patient care outcomes.

Gamma irradiation effects on photoluminescence and semiconducting properties of non-conventional heavy metal binary PbO–Bi2O3 glasses

Non-conventional heavy metal oxide glasses have attracted great interest owing to their unique optical properties and their radiation shielding behavior. Non-conventional glasses of main chemical composition (100 − x) PbO–xBi2O3 where x = 35, 30, 25, 20, 15, 10, and 5 were prepared through the conventional melting and annealing approach. X-ray diffraction measurements denoted the amorphous nature of the prepared glasses. The optical absorption in the UV–visible range recorded strong UV-near visible absorption spectra that correlated to trivalent Bi3+ ions. The optical band gap Eopt, Urbach energy ∆E, and the refractive index were identified for the prepared glasses employing the cognizant theories. The variations in the optical parameters have been associated with the increasing Bi2O3 and the doses of γ- irradiation. The photoluminescent properties of the prepared non-conventional binary Bi2O3–PbO glasses were recorded in the visible range after UV excitation and the color coordinates are located and distributed in the hue violet degree. FT-IR spectroscopic measurements before and after gamma irradiation were applied to investigate the structural changes in the binary heavy metal PbO–Bi2O3 glasses. FTIR data specified that the glass network is composed of different structural building units from BiO3/BiO6 and PbO3/PbO4 depending on the addition ratio between PbO and Bi2O3.

Electroluminescent and photoluminescent light-emitting diodes from carbon dots and device architecture optimization.

Light emission from carbon dots (CDs) is of great interest in both electroluminescence and photoluminescence. Herein, we construct electroluminescent and photoluminescent light-emitting diodes (LEDs) from emitters of CDs. The electroluminescent LED with host-guest-doped dual emissive layers (EMLs) of [poly(9-vinylcarbazole) (PVK)-CDs] × 2 gives satisfactory electro-optical properties, with maximum luminance of 560 cd m-2 at 16 V, luminous efficiency of 0.183 cd A-1, power efficiency of 0.082 lm W-1, and external quantum efficiency of 0.25%, which are superior to the counterparts with single-EML of CDs, single-EML of [PVK-CDs], and triple-EMLs of [PVK-CDs] × 3. These enhanced properties are rationally ascribed to optimization of the device architecture, carrier balance improvement, and reduction in concentration-induced quenching. The electroluminescent LEDs also show color evolution from PVK to CDs, and/or to the PVK/CDs interface, with increasing driving voltages, owing to incomplete energy transfer from PVK to CDs. Highly efficient photoluminescent LEDs with 365- and 395-nm UV excitation are demonstrated. With a CDs : polyvinyl pyrrolidone ratio of 1 : 3, the 365-nm excited photoluminescent LED gives a maximum luminance of 512 347 cd m-2 with a power efficiency of 25.2 lm W-1, while the 395-nm excited photoluminescent device gives a maximum luminance of 670 954 cd m-2 with a power efficiency of 22.0 lm W-1, with both showing yellow emission. Our experiments provide some new ideas for broadening CD applications and advancing LEDs.