Ultraviolet Excitation Research Articles

Optical and Scintillation Properties of Tb-Doped Rare-Earth Pyrosilicate Single Crystals

Series of 1.0% Terbium (Tb)-doped rare-earth pyrosilicate single crystals including Lu2Si2O7 (LPS), Y2Si2O7 (YPS), Gd2Si2O7 (GPS), and La2Si2O7 (LaPS) have been prepared by the floating-zone method. After the phase confirmation by powder X-ray diffraction, the properties are measured on both photoluminescence and scintillation aspects, including the photoluminescence emission contour graph and decay times, X-ray induced scintillation spectra and decay times, afterglow profiles, and the recently developed pulse height spectra for scintillators with millisecond decay time. The results indicate the multiple emissions from Tb3+ 4f-4f transition with the dominant emission at 540 nm (5D4 → 7F5) on both ultraviolet and X-ray excitation with the decay time around 2.6–5.6 and 1.3–3.2 ms, respectively. Under the γ-ray irradiation from 137Cs, the Tb-doped LPS, YPS, GPS, and LaPS have presented scintillation light yields of 20,700, 29,600, 95,600, and 47,700 ph/MeV with ±10%, respectively, which considerably very high among the oxide scintillators.

(Digital Presentation) Tailored Rare Earth-Doped Nanomaterials Toward Information Storage and Deep Learning Decoding

Lanthanide-doped nanoparticles have been considered as one of the most promising luminescent materials due to their excellent properties such as high photochemical stability, long-lived (μs-ms) luminescence, narrow emission band, and low toxicity.Moreover, benefiting from a unique electronic structure (4fn5s25p6 , n = 0-14), lanthanides have discrete energy levels and exhibit practical wavelength conversion via downshifting and upconversion processes. Hence, their emissions cover the spectral regions from ultraviolet (UV) to near-infrared (NIR).[1,2] Here, my talk is mainly devoted to our recent developments, including (1) recently, we present a new composition of Er3+-based upconversion nanoparticles with color-switchable output under irradiation with 980, 808, or 1535 nm light for information security. The variation of excitation wavelengths changes the intensity ratio of visible (Vis)/near-infrared 1535 nm (NIR-II) emissions. Taking advantage of the Vis/NIR-II multi-modal emissions of upconversion nanoparticles and deep learning, we successfully demonstrated the storage and decoding of visible light information in pork tissue.[3] (2) we construct heterostructured nanocomposites based on upconversion nanoparticles and EuSe semiconductors by using cation exchange method. It is generally considered that epitaxial growth is difficult when the lattice mismatch is large between two materials. In this case, the cation exchange of Eu3+ ions and other rare-earth ions could promote the formation of buffer layers to reduce the lattice mismatch and promote the heterogeneous epitaxial growth of EuSe on the upconversion nanoparticles. The heterostructured nanocomposites can emit tunable multicolor fluorescence under excitation of UV, continuous NIR, and pulsed NIR light. Based on the advantage of multiple tunable luminescence, the nanocomposites are designed as optical modules to load optical information. This work enables multi-dimensional storage of information and provides new insights into the design and fabrication of next-generation storage materials.

Complete B-site cation regulation accomplish UV-excited red phosphors in double perovskite oxides

As a widely explored red luminescent center, Eu3+ can reflect the features of the occupied lattice structure. Eu3+ ions energy levels and splitting in different hosts are mainly constrained by spin-orbit coupling and crystal field effects. This work reports an all-B-substituted perovskite-type red phosphor, and the role of the above two effects in this system is investigated by replacing Li+ (B1) and W6+ (B2) in BaLaLiWO6 with Na+ and Mo6+, respectively. Each sample's XRD and refinement results show that the all-B-site substitution does not affect the space group type; it only has a certain change in the unit cell parameters. The introduction of sodium ion makes the lattice expansion significantly enhance the intensity of the charge transfer band in the UV region. The introduction of Mo6+ significantly undermines the luminescence performance due to the influence of spin-orbit coupling. Subsequently, the symmetry changes of the position occupied by Eu3+ were verified by the red-orange ratio of Eu3+. The quantum yield of BaLaLi0·4Na0·6WO6: 0.30Eu3+ red phosphor under near ultraviolet excitation reaches 49.6%. Warm white light emission of color coordinates (0.363, 0.365) can be achieved by packaging with near UV chips, and the color rendering index can reach 83.3, which means that the phosphor has certain application prospects in WLED.

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations.

In most inorganic phosphors, increasing the concentration of activators inevitably causes the concentration quenching effect, resulting in reduced emission intensity at a high level of activator doping and the conventional practice is to limit the activator concentration to avoid the quenching. In contrast, SiAlON ceramics preserve their chemical composition over a very wide range of doping of activator ions, which favors the adjustment and optimization of the luminescence properties avoiding concentration quenching. Here, we investigate the photoluminescence properties of Ho-doped SiAlON (Ho-SiAlON) ceramics phosphors prepared by the hot-press method. Ho-SiAlON ceramics show strong green visible (554 nm) as well as infrared (2046 nm) broadband downshifting emissions under 348 nm excitation. It is shown that there is no concentration quenching, even at a very high level of Ho doping. The emission intensity of the 554 nm band increased two-fold when the Ho concentration is doubled. The results show that the Ho-SiAlON ceramics can be useful for efficient green phosphors.

Investigation into photoluminescence possessions of cool white light emanating novel Dy3+ complexes with β-ketoester antenna for advanced photonic devices

The synthesis of a novel series of five dysprosium complexes is reported in this work. This series contains one binary and four ternary complexes of dysprosium synthesized with chelating bidentate ligand 2-(methacryloxy)ethylacetoacetate and ancillary ligands i.e. neocuproine; 1,10-phenanthroline; 4,4′-dimethyl-2,2′-bipyridyl; 2,2′-bipyridyl and characterized by Fourier transform infrared, elemental analysis, energy dispersive X-ray analysis, ultra-violet visible spectroscopy and proton NMR spectroscopy. Under ultra violet excitation these complexes reveal characteristic bands of blue emission at 485 nm (4F9/2→6H15/2) and yellow emission at 576 nm (4F9/2→6H13/2). The theoretical values of band gap are obtained using density functional theory which are resembles with experimentally obtained values. Further, their superior practicability in white organic light emitting diodes (WOLEDs) is authenticated by the color purity, corelated color temperature and Commission International de I’Eclairage 1931 coordinates. The color coordinates are found to be consistent with white light coordinates of “National Television System Committee”.

Luminous LaAlO3 :Dy3+ perovskite nanomaterials: Synthesis, structural, and luminescence characteristics for white light-emitting diodes.

A single-phase perovskite LaAlO3 :Dy3+ phosphor was synthesized using a gel-combustion method at 600°C utilization with hexamethylenetetramine as a fuel. Further calcination of the samples was carried out (800 and 1000°C) to investigate the resultant effect on the crystalline and luminescence behaviour. The crystal structure had a cubic unit cell (space group Pm3̅m) and was examined using the Rietveld refinement and X-ray diffraction data. Additionally, Debye-Scherrer and Williamson-Hall equations were applied to determine other structural features. The particle size and morphology of phosphors were evaluated using transmission electron microscopy. Diffraction measurements were supported by the various metal-oxygen vibration modes studied with the help of Fourier transform infrared spectroscopy. Energy-dispersive X-ray analysis verified the chemical composition of synthesized sample. Luminescence spectra of the LaAlO3 :Dy3+ phosphors exhibited intense bands for 4 F9/2 →6 H15/2 (482 nm, bluish region) and 4 F9/2 →6 H13/2 (574 nm, yellowish region) transitions. Commission Internationale de L'Eclairage and correlated colour temperature data confirmed the cool-white emission of the samples under ultraviolet light excitation. The interesting and advantageous luminescence characteristics of LaAlO3 :Dy3+ phosphors make them potential materials for white light-emitting diodes.

Deciphering Photochemical Reaction Pathways of Aqueous Tetrachloroauric Acid by X-ray Transient Absorption Spectroscopy.

Photolysis reaction pathways of [Au(III)Cl4]- in aqueous solution have been investigated by time-resolved X-ray absorption spectroscopy. Ultraviolet excitation directly breaks the Au-Cl bond in [Au(III)Cl4]- to form [Au(II)Cl3]- that becomes highly reactive within 79 ps. Disproportionation of [Au(II)Cl3]- generates [Au(I)Cl2]-, which is stable for ≤10 μs. In contrast, intense near-infrared lasers photolyze water to generate hydrated electrons, which then reduce [Au(III)Cl4]- to [Au(II)Cl3]- at 5 ns. Hydrated electrons further induce a chain reaction from [Au(II)Cl3]- to [Au(0)Cl]- by successively removing one Cl-. The zero-valency Au anions quickly polymerize and condense to form Au nanoparticles, which become the dominating product after 400 s. Our results reveal that the condensation of zero-valency Au starts with dimerization of gold clusters coordinated with chloride ions rather than direct condensation of pristine Au atoms.

White Light-Emitting Diodes Based on One-Dimensional Organic-Inorganic Hybrid Metal Chloride with Dual Emission.

White-light emissive organic-inorganic hybrid metal halides (MHs) have shown promising potential applications in solid-state lighting. As one-dimensional (1D) MHs for white-light emission remain rare and the key role of halogen regulation in 1D hybrid MHs for broadband emission (BE) has not been well established yet, herein, we report a family of 1D hybrid MHs TMGPbX3 (TMG = 1,1,3,3-tetramethylguanidine, X = Cl-, Br-, or I-) to systematically explore the influence of halogen on crystal structures and photoluminescence (PL) properties in 1D organic-inorganic hybrid MHs. Under ultraviolet excitation, TMGPbBr3 and TMGPbI3 exhibit BE originating from self-trapped excitons (STEs), while TMGPbCl3 manifests the special blue-white dual emission, which is contributed by STEs in inorganic frameworks and free excitons (FEs) in the organic component. Different emission mechanisms of three 1D MHs are well demonstrated and compared. With a PL quantum yield (PLQY) up to 11.67%, a white light-emitting diode (WLED) based on TMGPbCl3 was fabricated to show its valuable application in solid-state lighting.

Crystal structure and temperature sensing performance of the novel Sr2Y8(1-x-y)(SiO4)6O2:xCe3+,yTb3+ thermometric phosphors

For the research of the thermometric performance, a series of Sr2Y8(1-x-y) (SiO4)6O2:xCe3+,yTb3+ phosphors were synthesized with the solid-state reaction method at N2/H2 atmosphere. The crystal structure, room and high temperature photoluminescence spectra, luminescence decay, CIE variation, energy transfer and thermometric performance have been investigated. With the ultraviolet light excitation, both the Ce3+ broadband spectrum and Tb3+ line spectra have been observed. With the increase of the Tb3+ concentration, the emission color chromaticity varies from dark blue to bright green for the series of Sr2Y8(1–0.07-y)(SiO4)6O2:0.07Ce3+,yTb3+ phosphors. Under high temperature, the Ce3+ emission intensity quenches faster than that of Tb3+. Based on the different temperature quenching speeds of Ce3+ and Tb3+, the fluorescence intensity ratio technique was used to evaluate the thermometric performance of the series of Sr2Y8(1–0.07-y) (SiO4)6O2:0.07Ce3+,yTb3+ phosphors. During the temperature range of 298–498 K, the maximum relative sensitivity values of the phosphors of yTb = 0.05, 0.08, 0.1, 0.15, 0.2, 0.25 were calculated as 0.65, 0.69, 0.74, 0.71, 0.66, 0.6% K−1, which are much better than the recommended value of 0.30% K−1 for the practical application. The physical mechanisms for the Ce3+/Tb3+ excitation and emission, energy transfer and temperature quenching have been discussed. Sr2Y8(1-x-y) (SiO4)6O2:xCe3+,yTb3+ phosphors are the candidate thermometric probes for the non-contact temperature sensing applications.

Design of K2SrCa(PO4)2-x(BO3)x:Eu2+ phosphors with full-visible spectrum by crystal structure modification

In recent years, much attention has been paid to the development of rare-earth-activated borophosphate phosphors for white light-emitting diodes (LEDs). Herein, Eu2+ single-doped K2SrCa(PO4)2-x (BO3)x white phosphors with full-visible-spectrum continuous emission in the range of 400 nm–720 nm were developed by the modification of the local structure in the crystal. The structural variation resulted from the substitution of (PO4)3- ions by (BO3)3- in host lattice were investigated in detail by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, the phase structure of sample was also confirmed by the Rietveld method, indicating its Rhombohedral structure with the R-3c space group and the occupation of K and Ca sites by Eu2+ ions, then combined luminescence lifetime decay, revealing insights of site-selective occupation of Eu2+ in the borophosphate white light phosphors. The emission spectra of K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor exhibited full-visible-spectrum continuous emission centered at 455 and 595 nm by adjusting the concentration of the (BO3)3- groups under near ultraviolet excitation at 365 nm. Especially, the WLEDs obtained from the broad-spectrum phosphors showed ultra-high color quality of color rendering index (CRI) values (Ra = 95, R9 = 66, and R13 = 95) and excellent fidelity/gamut index values (Rf = 94 and Rg = 98), which was almost similar to sunlight streaming. The investigation results indicated that the device by using as-prepared K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor could be a potential candidate for full-spectrum lighting.

Designing X-ray-Excited UVC Persistent Luminescent Material via Band Gap Engineering and Its Application to Anti-Counterfeiting and Information Encryption.

Persistent luminescent materials (PLMs) are promising candidates for the anti-counterfeiting and information encryption field. However, ultraviolet (UV) excitation and visible emission are partially responsible for enabling information that has been encrypted to combat counterfeiting to be accessed by trial and error, resulting in imitation and information leakage. Here, we propose the possibility of controlling the persistent luminescent (PersL) emission spectra and its excitation light source with the use of band gap engineering, while obtaining X-ray exciting, not UV exciting UV PLM for advanced anti-counterfeiting and encryption application. Cationic substitution was used to adjust the width of the band gap of Lu(X)O4 (X = V, Nb, Ta, and P) from ∼4 to 9 eV. In addition, Bi3+ was introduced into the host as an emitter, which enabled the PersL emission spectra to be modulated from ∼550 to 230 nm. Among these PLMs, LuPO4:Bi3+ has unique optical properties. Under UV excitation, LuPO4:Bi3+ exhibits weak, inconspicuous visible down-conversion luminescence (DCL), without PersL ceasing once excitation is discontinued. Interestingly, LuPO4:Bi3+ displays UV PersL after X-ray excitation, and human eyes are insensitive to UV PersL, which requires specialized optical equipment to detect. A proof-of-concept assessment of LuPO4:Bi3+ for anti-counterfeiting and information encryption applications demonstrated its suitability in this regard.

Single-kernel classification of deoxynivalenol and zearalenone contaminated maize based on visible light imaging under ultraviolet light excitation combined with polarized light imaging

Deoxynivalenol and zearalenone contamination in maize poses a threat to food safety. Thus, the development of a cost-effective and non-destructive method to classify deoxynivalenol and zearalenone contaminated maize is an important research issue. Natural deoxynivalenol and zearalenone contaminated maize were randomly selected for this experiment. Visible light imaging under ultraviolet light excitation combined with polarized light imaging was used to extract texture and color features from the endosperm and germ sides. And six classification models were established for the single-kernel classification of 1035 contaminated maize. The results indicated that the optimal detection surface was the endosperm side, and the optimal model was SVM with a classification accuracy of 88.1%. Then, local feature analysis of images and mycotoxin concentrations verification experiment were used to reduce secondary contamination and further evaluate the performance of the model, respectively. This method can be verified to be effective in identifying three deoxynivalenol and zearalenone contamination levels of maize, and can also reduce the costs of test stands.

Automated assessment of breast margins in deep ultraviolet fluorescence images using texture analysis.

Microscopy with ultraviolet surface excitation (MUSE) is increasingly studied for intraoperative assessment of tumor margins during breast-conserving surgery to reduce the re-excision rate. Here we report a two-step classification approach using texture analysis of MUSE images to automate the margin detection. A study dataset consisting of MUSE images from 66 human breast tissues was constructed for model training and validation. Features extracted using six texture analysis methods were investigated for tissue characterization, and a support vector machine was trained for binary classification of image patches within a full image based on selected feature subsets. A weighted majority voting strategy classified a sample as tumor or normal. Using the eight most predictive features ranked by the maximum relevance minimum redundancy and Laplacian scores methods has achieved a sample classification accuracy of 92.4% and 93.0%, respectively. Local binary pattern alone has achieved an accuracy of 90.3%.

Double-Network Luminescent Films Constructed Using Sulfur Quantum Dots and Lanthanide Complexes.

Although UV light-switchable luminescent films are of importance for application in soft optical devices and anticounterfeiting labels, there are still challenges in developing such films integrated with outstanding luminescent property, high self-healing efficiency, and simultaneously excellent mechanical strength. Herein, double-network (DN) luminescent films are designed and constructed via an intermolecular hydrogen bond crosslinking strategy of poly(ethylene glycol) (PEG) in sulfur quantum dots (S-QDs) and polyurethane (PU), where S-QDs ("stone" one) play dual roles of acting both as a soft segment to crosslink another segment PU ("bird" one) and also as the origin of a luminescence center ("bird" two) in films. In addition, lanthanide(III) complexes (LnCs, Ln═Eu3+, Tb3+) are employed as another emission source to embed in the films and switch the emission colors of DN films from the multicolor (red-yellow-green) of LnCs to the blue color of S-QDs by changing the ultraviolet excitation wavelength from 254 to 365 nm. It is worth noting that the crosslinking network strategy can effectively prevent S-QDs and LnCs from aggregating or leaking and enable both luminescence centers to homogeneously distribute, resulting in luminescent DN films possessing extraordinary UV light-switchable luminescence, improved mechanical property, and excellent self-healing ability. This work presents a viable method for the design and fabrication of luminescent films with multifunctional applications in flexible robotics, wearable devices, and dual-luminescent anticounterfeiting materials.

External-field-dependent tunable emissions of Er3+-In3+ Co-doped Cs2AgBiCl6 for applications in anti-counterfeiting

Anti-counterfeiting materials play an irreplaceable role in information security and reducing national and enterprise losses, while the fluorescent anti-counterfeiting materials are widely used because of their feasible and flexible designs, visibility, easy identification and difficulty in cracking. For enhancing the security of fluorescent anti-counterfeiting materials, it is a popular choice to increase the modulus throung combining the up-conversion (UC) and down-conversion (DC) together with dynamic luminescence in one. Herein, Er3+ and In3+ co-doped Cs2AgBiCl6 phosphors with UC and DC emissions were successfully developed, in which Er3+ ions are responsible for the green UC emission under the excitation of 980 or 1550 nm laser while In3+ take the responsibility of enhancing yellow DC emission with 365 nm near ultraviolet light excitation. Furthermore, the DC luminescence color gradually changes to white from yellow as the ambient temperature increases from room temperature to 490 K. The potential application of the present samples in the field of anti-counterfeiting was evaluated by designing different patterns with the help of screen printing technology, which implied that the present sample provided a feasible and facilitated way to address the counterfeit issues.

Mn2+-Activated Afterglow in a Transparent Perovskite Crystal.

Transparent crystals of long afterglow are keenly desired for advanced applications involving three-dimensional information storage and volumetric display. Here, we report the growth of a perovskite crystal, Cs2NaInCl6:Mn, via a facile hydrothermal reaction. The crystal featured a high transparency up to 90% in a broad range from 400 to 750 nm. Upon ultraviolet (UV) excitation, the crystal exhibited an overlapped emission from both self-trapped exciton (STE) and Mn ions. An unusual energy transfer from Mn ion to STE was revealed through steady-state and transient photoluminescence (PL) spectra. Through concentration tuning, the afterglow duration was extended to 2500 s with a signal-to-noise ratio over 20. The single dopant of Mn ions was found to play two roles in afterglow mechanism, including both electron traps and emitting activators. This work provided a facile method to synthesize transparent crystals of persistent luminescence, opening many avenues for three-dimensional information storage and volumetric display.

Artificial optoelectronic synaptic characteristics of Bi2FeMnO6 ferroelectric memristor for neuromorphic computing

Photoelectric synapse is a new type of artificial synapse that combines light pulse excitation and electrical pulse excitation, and is an important component for the development of neuromorphic hardware. In this work, the Bi2FeMnO6 ferroelectric artificial synapse with optoelectronic response is reported. It can generate an excitatory post-synaptic current through ultraviolet light irradiation and then modulate the excitatory post-synaptic current through ferroelectric polarization, thereby realizing a photo-ferroelectric dual-control synapse. A training method based on ultraviolet excitation and ferroelectric enhancement is proposed, which greatly reduced the number of training pulses and increased the plasticity of the synapse. The optimized spike scheme based on ferroelectricity is proposed, which made the synapse have very linear weight adjustment function. This synapse is used to build a convolutional neural network, which can achieve 98.80% recognition accuracy on the MNIST dataset. In addition, the ferroelectricity and multi-level resistive switching effect of synapse have also been reported.

Enhanced photosensitivity of heterostructure SiO2/Bi2WO6/GO composite nanoparticles

The Bi2WO6, Bi2WO6@GO, SiO2/Bi2WO6, and SiO2/Bi2WO6@GO nanocomposites were synthesized using a simple process. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR), EDX mapping investigations confirmed the successful synthesis, related chemical bonding, and elements in the structure. According to the TEM and FESEM images, composite nanoparticles consisting of cubic-like Bi2WO6 and regular spherical-like particles of SiO2 between the GO sheets. The strong emission color of green under ultraviolet excitation was obtained. The radiation sensitivity of the SiO2/Bi2WO6@GO nanocomposite under the 241Am alpha source was the best compared with other samples. It was observed that the incorporation of SiO2 and reduced graphene oxide in composite structures can lead to further sensitivity of ionizing radiation and luminescence intensity at room temperature. Furthermore, prepared SiO2/Bi2WO6 NPs showed a high decolorization efficiency of MB dye (98.2%) under UVA irradiation for 100 min. These results present a promising potential for applications in photonic devices.

Structural and luminescence studies of titanium co-doped SrY2 O4 :Eu phosphors.

Here, europium-doped (1 to 11 mol%) and titanium (1 to 5mol%)co-doped SrY2 O4 :Eu phosphors were synthesized using solid-state reaction method. The synthesized samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) techniques for structural, morphological, functional group, and photoluminescence studies, respectively. XRD patterns confirmed the formation of pure phase SrY2 O4 at 1300°C and structural parameters were further determined using Rietveld refinement. FESEM micrographs revealed that doped and co-doped samples had different morphological features. All the samples were excited at ultraviolet light excitation and emission spectra consisted of peaks corresponding to the Eu ions. The maximum PL intensity was observed for 9mol% of Eu ions and 3mol% co-doping of Ti ions. The synthesized phosphors have potential applications in optoelectronics and display devices.

Excitation-dependent perovskite/polymer films for ultraviolet visualization

Ultraviolet (UV) visualization has extensive applications in military and civil fields such as security monitoring, space communication, and wearable equipment for health monitoring in the internet of things (IoT). Due to their remarkable optoelectronic features, perovskite materials are regarded as promising candidates for UV light detecting and imaging. Herein, we report for the first time the excitation-dependent perovskite/polymer films with dynamically tunable fluorescence ranging from green to magenta by changing the UV excitation from 260 to 380 nm. And they still render dynamic multi-color UV light imaging with different polymer matrixes, halogen ratios, and cations of perovskite materials. The mechanism of its fluorescence change is related to the chloride vacancies in perovskite materials. A patterned multi-color ultraviolet visualization pad is also demonstrated for visible conversion of the UV region. This technique may provide a universal strategy for information securities, UV visualizations, and dynamic multi-color displays in the IoT.