Sharp Emission Research Articles

Synthesis of carbohydrate based polythiophene graft poly(N,N-dimethylaminoethyl methacrylate)-co-poly(GLU-HEM) copolymer for lectin sensing

Sensing of lectins are utmost necessary for its inflammatory, digestive disorder, gut pains and toxicity to human beings and for this purpose we have chosen polythiophene (PT) for its exciting optoelectronic properties. Because of precise carbohydrate specificities of lectin and to make PT water soluble for sensing of lectin, we have synthesized polythiophene-g-poly(N,N-dimethylaminoethyl methacrylate) -co-poly(glucose-hydroxyethyl methacrylate) (PT-g-pDMAEMA-co-pGLU-HEM), [PTDG]) from polythiophene macroinitiator (PTI) by copolymerizing DMAEMA and GLU-HEM monomers mixture with CuCl/HMTETA catalyst/ligand followed by hydrolysis using alcoholic NaOMe solution. The Mn of PTI was 38000, polydispersity 2.5, head-tail (H-T) regioregularity 70 mol % and Mn of unhydrolyzed PTDG is 98,900. The UV-Vis spectra of PTDG solution shows two absorption peaks at 430 and 462 nm but it shows a sharp emission peak at 544 nm which quenches with increasing pH. Concanavalin A (ConA) shows an absorbance peak at 278 nm and with addition of PTDG solution absorbance intensity increases showing hypochromic effect. Benesi–Hildebrand plot of reciprocal molar extinction coefficients with concentration suggests 1:1 complex formation between PTDG and ConA. With addition of ConA fluorescence quenching of PTDG solution occurred and using the fluorescence intensity ratio vs concentration plot the limit of detection (LOD) of Con A lectin is found to be 57 µg/L and storing the polymer solution for two months exhibits good durability. The morphology of PTDG changes from vesicle to compound micellar aggregate on addition of Con A lectin.

Accessing a Long‐Fluorescence‐Lifetime BODIPY Dye via Efficient Förster Resonance Energy Transfer Induced by Host‐Guest Doping

AbstractThe development of pure organic room temperature phosphorescence (RTP) luminophores with high quantum yield and long emission lifetime has attracted considerable attention due to their extensive optoelectronic and biomedical applications. The commonly used BODIPY dyes have strong UV‐Vis absorption, a relatively sharp emission peak, high quantum yield, and a short emission lifetime. By expending the molecular doping approach, we herein successfully achieved a long‐fluorescence‐lifetime BODIPY dye via efficient Förster resonance energy transfer (FRET) from RTP molecule o‐AI‐Cz to the short‐lived fluorescence emitter Bodipy‐2I. This host‐guest material possessed an ultralong lifetime of up to 595 ms and a long emission wavelength under ambient conditions, which has great potential in data encryption and anti‐counterfeiting applications. Moreover, this easily prepared FRET system exhibited an efficient response to two‐photon excitation in living cell fluorescence imaging.

A Multiple Resonance Emitter Integrating Para‐B‐π‐B′/Meta‐N‐π‐N Pattern via an Unembedded Organoboron Decoration for Both High‐Efficiency Solution‐ and Vacuum‐Processed OLEDs

AbstractMultiple resonance (MR)‐type thermally activated delayed fluorescence (TADF) emitters have promising prospects for high‐color‐purity organic light‐emitting diodes (OLEDs), but they are seldom attempted in the fabrication of solution‐processed devices. In addition, another issue with MR‐TADF emitters is that their heteroatom patterns are very limited, hampering their diversity. Herein, a novel double boron (B)‐containing MR‐TADF paradigm that merges an unembedded organoboron unit and a B‐embedded π‐fused MR framework into one system, furnishing a unique para‐B‐π‐B′/meta‐N (nitrogen)‐π‐N molecular pattern is proposed. Based on this, a proof‐of‐concept molecule, BNB′‐1, is developed, simultaneously achieving a bright sharp emission peaking at 540 nm with a full width at half maximum (FWHM) of only 24.5 nm/98 meV, a nearly unity photoluminescence quantum yield and excellent organic solubility. A solution‐processed OLED using BNB′‐1 emitter delivers an impressive external quantum efficiency (EQE) as high as 36.2% with an emissive FWHM of only 30.0 nm/0.13 eV at ≈540 nm; both parameters set new records among the ever‐reported solution‐processed MR‐OLEDs. Moreover, BNB′‐1 also obtains a superhigh EQE of 40.3% in vacuum‐processed OLEDs, surpassing all MR‐OLEDs in the similar emission region. This work provides an interesting solution to develop high‐performance solution‐processable MR‐TADF emitters with diverse heteroatom patterns.

NLO and white light emission in AuNPs reinforced Li2O–Bi2O3–B2O3–P2O5 glasses: Role of surface plasmonic resonance AuNPs

Significant optical nonlinearities in amorphous nanocomposites are essential for developing advanced communications and photonic devices. In this regard, the borate glasses are considered substantial and readily available commercial hosts. The present work demonstrates the white light emission and decay properties in lithium bismuth boro-phosphate glasses reinforced with gold nanoparticles (AuNPs) prepared via melting and quenching technique. Also, their non-linear optical properties are evaluated in the present study. Numerous characterization methods were used to extensively examine the produced glasses, including XRD, HR-TEM, FTIR, XPS, MAS-NMR, DSC, UV–Visible, Photoluminescence, and Z-scan techniques. Following the addition of AuNPs into the glass matrix, an increase in the refractive index and density of the glasses was observed. The amorphous features of the glass sample are disclosed by XRD examination, and DSC research demonstrates the thermal stability of the glasses after the addition of AuNPs, as shown by the rise in Tg values from 459 °C to 486 °C. HR-TEM results reveal the presence of Au metal nanoparticles having a cubic crystal structure with an average size of 14 nm, while XPS analysis shows that the valence of Au is 0, i.e. Au0 or, in other words, the metallic nature of gold in glasses. FTIR, MAS-NMR, and UV–Visible spectral studies demonstrate the substantial modifications in the physical, structural, and optical properties brought about by incorporating AuNPs into the glass matrix. The PL spectra of glasses containing AuNPs show three distinct, sharp emissions at 494, 611, and 738 nm, out of which the blue emission (494 nm) is found to be predominant and has an overall emission in the region of yellow on the CIE diagram with an average lifetime of 12.23 μs. Glasses containing AuNPs have a white light correlated colour temperature (CCT) of 5129 K and CIE chromaticity (x, y) coordinates of (0.346, 0.413). Additionally, we utilized a Z-scan technique to measure the nonlinear absorption coefficient and nonlinear refractive index. Our experimental data show that the values obtained are consistent with the theoretical closed and open aperture values. Based on our findings, it appears that the glasses we prepared have the potential to be utilized in optical switching applications.

Imaging Giant Vesicle Membrane Domains with a Luminescent Europium Tetracycline Complex.

Microdomains in lipid bilayer membranes are routinely imaged using organic fluorophores that preferentially partition into one of the lipid phases, resulting in fluorescence contrast. Here, we show that membrane microdomains in giant unilamellar vesicles (GUVs) can be visualized with europium luminescence using a complex of europium III (Eu3+) and tetracycline (EuTc). EuTc is unlike typical organic lipid probes in that it is a coordination complex with a unique excitation/emission wavelength combination (396/617 nm), a very large Stokes shift (221 nm), and a very narrow emission bandwidth (8 nm). The probe preferentially interacts with liquid disordered domains in GUVs, which results in intensity contrast across the surface of phase-separated GUVs. Interestingly, EuTc also alters GM1 ganglioside partitioning. GM1 typically partitions into liquid ordered domains, but after labeling phase-separated GUVs with EuTc, cholera toxin B-subunit (CTxB), which binds GM1, labels liquid disordered domains. We also demonstrate that EuTc, but not free Eu3+ or Tc, significantly reduces lipid diffusion coefficients. Finally, we show that EuTc can be used to label cellular membranes similar to a traditional membrane probe. EuTc may find utility as a membrane imaging probe where its large Stokes shift and sharp emission band would enable multicolor imaging.

Fluorescent aggregate structure revealed in bisphenol F epoxy thermoset

Bisphenol F (BPF) epoxy resin is a prepolymer component of thermosets used in construction of reinforced carbon fiber composites (RCFC). The fluorescence of this resin can provide information about chemical and structural alterations of the thermoset from thermal or mechanical damage. While some work has investigated the fluorescence spectra of bisphenol A epoxy resin, a structural analog of BPF, none have studied BPF. The purpose of this study is to investigate the baseline fluorescence spectra of the BPF epoxy resin for features that could be utilized for monitoring damage and structural alterations. Bisphenol F epoxy resin was found to have two emission peaks with a broad peak centered at 410 nm and a sharp peak centered at 550 nm. The broad emission peak was identified as the fluorescence from BPF epoxy monomer while the sharp emission peak was found to be from an aggregate structure present in the epoxy resin. It is hypothesized that this structure is an H-aggregate based on the emission features and structural stability of the aggregate compared to the alternative J-aggregate which was determined via density functional theory calculations. The H-aggregate was found to persist into one of the cured thermoset formulations evaluated but was lost when exposed to elevated temperatures below thermal degradation of the thermoset. This loss of aggregate structure was due to polymer network rearrangement. This new fluorescence signature can be used as an indicator of polymer network rearrangement from thermal exposure which may alter the expected material performance and precede thermal degradation.

Metal plasmon-enhanced lanthanide fluorescent nanoparticles for monitoring aqueous copper ions

Lanthanide-doped nanomaterials displaying intense, explicit, and long-lasting photoluminescence (PL) have gained much attention in sensing and imaging applications. In this work, europium complex Eu(dibenzoylmethane)3(1,10-phenanthroline) was integrated into core-shell magnetoplasmonic nanoparticles (Ag@Fe3O4 MagPlas NPs), forming a photoluminescent MagPlas nanostructure with uniform morphology, sharp PL emission profile, and distinct magnetic response. The Eu-doped MagPlas NPs (Eu-MagPs) with Ag-core exhibited an enhancement of PL intensity and lifetime compared to the non-plasmonic counterpart, owing to the metal plasmon-induced fluorescence enhancement. Moreover, the quenching phenomenon of the Eu-MagP probe was utilized as a platform for active quantification of metal ion concentration, exclusively Cu2+, in aqueous samples. The luminescence intensity from the Eu-doped MagPlas NP was proportionally quenched by Cu2+ in the working range of 0–2 ppm with negligible influences of other common cations and anions. Static quenching was investigated as the main mechanism for selective detection, in which the presence of quenchers did not affect the luminescent lifetime of the hybrid nanostructure. Moreover, Eu-MagPs were integrated into polyacrylamide hydrogels with enhanced customizability toward the varied amounts of Cu2+. This fluorescent MagPlas structure, therefore, can be utilized as versatile, waste-free, fully recoverable testing assays or chemical sensors for on-site environmental analysis, and water quality control.

Multi-color luminescence of Sm3+ -doped Na2 YMg2 V3 O12 phosphor potentially applicable in white-LEDs.

A novel multi-color emitting Na2 YMg2 V3 O12 :Sm3+ phosphor was synthesized using a solid-state reaction, and its crystal structure, luminescence properties, and thermal stability were studied. Charge transfer within the (VO4 )3- groups in the Na2 YMg2 V3 O12 host led to a broad emission band between 400 and 700 nm, with a maximum at 530 nm. The Na2 Y1-x Mg2 V3 O12 :xSm3+ phosphors exhibited a multi-color emission band under 365 nm near-ultraviolet (near-UV) light, consisting of the green emission of the (VO4 )3- groups and sharp emission peaks at 570 nm (yellow), 618 nm (orange), 657 nm (red), and 714 nm (deep red) of Sm3+ ions. The optimal doping concentration of Sm3+ ions was found to be 0.05 mol%, and the dipole-dipole (d-d) interaction was primarily responsible for the concentration quenching phenomenon. Using the acquired Na2 YMg2 V3 O12 :Sm3+ phosphors, commercial BaMgAl10 O17 :Eu2+ blue phosphor, and a near-UV light-emitting diode (LED) chip, a white-LED lamp was designed and packaged. It produced bright neutral white light, manifesting a CIE coordinate of (0.314, 0.373), a color rendering index (CRI) of 84.9, and a correlated color temperature (CCT) of 6377 K. These findings indicate the potential of Na2 YMg2 V3 O12 :Sm3+ phosphor to be used as a multi-color component for solid-state illumination.

Characterization of europium doped yttrium nano-oxide prepared by plasma electrolysis in nitrate solution under air atmosphere at room temperature

Europium-doped yttrium oxide is widely used because its unique optical properties, excellent thermal stability, and chemical stability. This paper reports a process for preparing a Y2O3:Eu3+ red fluorescent material through plasma discharge electrolysis at room temperature in a normal atmosphere and a 0.38 M Y(NO3)3 - 0.02 M Eu(NO3)3 mixed rare earth nitrate solution. Several techniques, including emission spectroscopy, X-ray diffraction, TG-DSC thermal analysis, Fourier transform infrared spectroscopy and photoelectron spectroscopy, were performed to characterize the electrolysis process and the obtained products. The results show that the electrolytic products were mainly composed of Y(OH)3, the electrolytic hydroxide products were not obviously granular, and Eu was uniformly distributed in the products. After heat treatment at 400–900 °C, cubic phase yttrium oxide was formed, and the products were irregular spherical, with particle sizes between 30 and 200 nm. After annealing at 800 °C, the products showed strong red emission at 612 nm, corresponding to 5D0→7F2 excitation. In addition, charge transfer band (CTB) absorption was observed in the excitation spectrum, and the emission spectra of fluorescent materials also showed some sharp emission bands generated by the 5D0→7FJ (J = 0,1,3,4) transition. The colour coordinate of the Y2O3:Eu3+ powder produced by plasma electrolysis is close to the standard red coordinate, showing excellent colour properties.

Investigation on Optical, Electrical, Third Harmonic Generation and Hirshfeld Analysis Characteristics of Novel Organic 3‐Amino‐1H‐1,2,4‐Triazole 3,5‐Dinitrobenzoic Acid Monohydrate (3ATDM) Crystal for Nonlinear Optical (NLO) Applications

AbstractThe organic 3‐amino‐1H‐1,2,4‐triazole 3,5‐dinitrobenzoic acid monohydrate (C9 H10 N6 O7) (H2O) (3ATDM) single crystal is synthesized and grown using the slow evaporation solution technique (SEST), for the first time. Single crystal X‐ray diffraction (SXRD) analysis indicated that the 3ATDM crystal has the characteristics of the noncentrosymmetric Pc space group of the monoclinic crystal system. The crystal have good optical characteristics as observed using UV‐visible‐near infrared (NIR) analysis; the transmittance wavelength region is in the range of 200–1000 nm. Sharp emission peaks are observed in the photoluminescence spectrum; this is indicative of ultraviolet (UV) emission. Thermogravimetric and differential thermal analysis (TG‐DTA) is used to evaluate the thermal behavior. The 3ATDM crystal is thermally stable up to 207 °C; the first endothermic peak appeared at 150 °C. The dielectric loss (tan δ) and dielectric constant (ε') are measured as a function of frequency. Vickers microhardness analysis is used to characterize the mechanical strength of the 3ATDM crystal. The third‐order nonlinear optical properties such as absorption coefficient (β), refractive index (n2), and susceptibility (χ (3)) are evaluated through the Z‐scan technique at 532 nm, using a continuous wave (CW) solid‐state laser.

Spectral characterization and energy transfer study of Nd3+/Yb3+ in borosilicate glasses

Very sharp emission in near infrared region is observed for Nd3+/Yb3+ codoped 60B2O3-10SiO2-5PbO-10Al2O3-10Li2O-5ZnO (BSPbLAZ) glasses which were prepared by melt-quenching method along with Nd3+ doped BSPbLAZ glass. Photoluminescence excitation (PLE) spectra of 1 mol% of Nd2O3 doped BSPbLAZ glass shows intense band at 584 nm at an emission wavelength of 1062 nm. Photoluminescence emission (PL) spectra for 1 mol% of Nd2O3 doped BSPbLAZ glass at an excitation wavelength of 584 nm shows three characteristics emission bands in NIR range, 4F3/2→4I9/2, 4I11/2 and 4I13/2, most intense among these being the one at 1062 nm corresponding to 4F3/2→4I11/2. In the codoped system (Nd2O3/Yb2O3), prominent emission bands for Nd3+ are observed at 887, 1062 and 1336 nm corresponding to 4F3/2→4I9/2, 4I11/2 and 4I13/2 respectively, while for Yb3+ ions transition is observed at 980 nm corresponding to 2F5/2→2F7/2. Detailed investigation of characteristics like NIR emission, lifetime and energy transfer efficiency on increment of Yb2O3 doping concentration helps in understanding the utility of these glasses in the fields like photonic and optical devices. In BSPbLAZ glass Yb3+ can be easily sensitized by Nd3+ ions on account of its 4f-4f transitions. These factors provide healthy possibility for usage of Nd3+/Yb3+codoped BSPbLAZ glasses as multiple pump channel sources for laser fiber system based on Yb3+ ions.

Temperature dependence of luminescence characteristics from Eu doped Ga2O3 thin films excited by synchrotron radiation source

Ga2O3 thin film with Eu doping was prepared on p-Si substrate by pulsed laser deposition to investigate the temperature dependence of photoluminescence from Eu3+ and host. The obtained Ga2O3:Eu thin film has a polycrystalline monoclinic structure and smooth surface. The film exhibits multiple sharp emissions originating from Eu3+ dopants, as well as broad defect-related emissions in the UV-green region from Ga2O3 host. With increasing the temperature from 21 K to RT, the red emission from Eu3+ keeps unchanged in the wavelength, and remains ∼55% PL intensity. Meanwhile, Ga2O3 defect-related UV and blue emissions experience a strong thermal quenching and a distinct red shift following the Varshni equation and Bose–Einstein expression. These experimental data will provide reliable guide for fabricating efficient luminescent devices based on rare-Earth doped Ga2O3.

Enhanced Photoluminescence and Random Lasing Emission in TiO2-Decorated FAPbBr3 Thin Films.

Herein, titanium-dioxide-decorated organic formamidinium lead bromide perovskite thin films grown by the one-step spin-coating method are studied. TiO2 nanoparticles are widespread in FAPbBr3 thin films, which changes the optical properties of the perovskite thin films effectively. Obvious reductions in the absorption and enhancements in the intensity of the photoluminescence spectra are observed. Over 6 nm, a blueshift of the photoluminescence emission peaks is observed due to 5.0 mg/mL TiO2 nanoparticle decoration in the thin films, which originates from the variation in the grain sizes of the perovskite thin films. Light intensity redistributions in perovskite thin films are measured by using a home-built confocal microscope, and the multiple scattering and weak localization of light are analyzed based on the scattering center of TiO2 nanoparticle clusters. Furthermore, random lasing emission with sharp emission peaks is achieved in the scattering perovskite thin films with a full width at the half maximum of 2.1 nm. The multiple scattering of light, the random reflection and reabsorption of light, and the coherent interaction of light within the TiO2 nanoparticle clusters play important roles in random lasing. This work could be used to improve the efficiency of photoluminescence and random lasing emissions, and it is promising in high-performance optoelectrical devices.

Molecular and Supramolecular Designs of Organic/Polymeric Micro-photoemitters for Advanced Optical and Laser Applications.

ConspectusFor optical and electronic applications of supramolecular assemblies, control of the hierarchical structure from nano- to micro- and millimeter scale is crucial. Supramolecular chemistry controls intermolecular interactions to build up molecular components with sizes ranging from several to several hundreds of nanometers using bottom-up self-assembly process. However, extending the supramolecular approach up to a scale of several tens of micrometers to construct objects with precisely controlled size, morphology, and orientation is challenging. Especially for microphotonics applications such as optical resonators and lasers, integrated optical devices, and sensors, a precise design of a micrometer-scale object is required. In this Account, we review the recent progress on precise control of microstructures from π-conjugated organic molecules and polymers, which work as micro-photoemitters and are suitable for optical applications.After the introduction on the importance of the control of the hierarchical structures from molecular assembly, we review supramolecular methodology for assembling molecules and supramolecules to form microstructures such as spheres and polygons with precisely controlled morphology and molecular orientations. The resultant microstructures act as anisotropic emitters of circularly polarized luminescence. We report that synchronous crystallization of π-conjugated chiral cyclophanes forms concave hexagonal pyramidal microcrystals with homogeneous size, morphology, and orientation, which clearly paves the way for the precise control of skeletal crystallization under kinetic control. Furthermore, we show microcavity functions of the self-assembled micro-objects. The self-assembled π-conjugated polymer microspheres work as whispering gallery mode (WGM) optical resonators, where the photoluminescence exhibits sharp and periodic emission lines. The spherical resonators with molecular functions act as long-distance photon energy transporters, convertors, and full-color microlasers. Fabrication of microarrays with photoswitchable WGM microresonators by the surface self-assembly technique realizes optical memory with physically unclonable functions of WGM fingerprints. All-optical logic operations are demonstrated by arranging the WGM microresonators on synthetic and natural optical fibers, where the photoswitchable WGM microresonators act as a gate for light propagation via a cavity-mediated energy transfer cascade. Meanwhile, the sharp WGM emission line is appropriate for utilization as optical sensors for monitoring the mode shift and mode splitting. The resonant peaks sensitively respond to humidity change, absorption of volatile organic compounds, microairflow, and polymer decomposition by utilizing structurally flexible polymers, microporous polymers, nonvolatile liquid droplets, and natural biopolymers as media of the resonators. We further construct microcrystals from π-conjugated molecules with rods and rhombic plates, which act as WGM laser resonators with light-harvesting function. Our developments, precise design and control of organic/polymeric microstructures, form a bridge between nanometer-scale supramolecular chemistry and bulk materials and pave the way toward flexible micro-optics applications.

Effect of 100 MeV Ni7+ ion irradiation on photoluminescence of [formula omitted] and [formula omitted] phosphor

Aluminum oxide phosphors were synthesized by solution combustion method using urea and glycine as fuel. XRD results show that the sample synthesized with urea as a fuel is α-Al2O3 and glycine as a fuel is γ-Al2O3 with rhombohedral (R-3c) and cubic (Fd-3m) structures, respectively. The PL spectra of unirradiated and Ni7+ ions irradiated α-Al2O3 show a broad peak between 1.92 and 3.2 eV with maxima at 2.25 eV. This broad emission is assigned to the combination of F2 and F22+ centers. In addition, two sharp emissions observed at 1.83 eV (678 nm) and 1.78 eV (695) are due to R-lines of Mn4+ and Cr3+ respectively. The PL intensity is enhanced after Ni7+ ion irradiation in α-Al2O3 and the highest intensity is observed for 1 × 1012 Ni7+ cm−2. PL intensity decreases beyond this fluence. Unirradiated γ-Al2O3 samples have greater PL intensity, which decreases with Ni7+ ion irradiation. PL emissions of R-lines of Mn4+ and Cr3+ are missing in γ-Al2O3 due to a lower crystal field in the gamma phase.

Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors.

Europium ion-activated calcium silicate phosphors (Ca2SiO4:Eu3+) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca2SiO4:Eu3+ phosphors was controlled between 20 and 200 nm by precursor silicate particle sizes. Systematic studies to determine morphology, crystal phase, and photoluminescence (PL) were carried out for all the phosphors, and their optical efficiencies were compared. We found that the luminescence intensity and emission wavelength of Ca2SiO4:Eu3+ phosphors depend on their particle sizes. Particularly, the Ca2SiO4:Eu3+ synthesized with 20 nm silica seed contains the most intense red emission, high color purity, and high PL quantum yield. For the 20 nm-sized Ca2SiO4:Eu3+ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of 5D0 → 7F4 emission (712 nm) is explained by structural distortion arising from silicate particle size reductions. We show that the obtained phosphor is a suitable candidate for solid-state lighting as a red component through CIE chromaticity coordinate and color purity measurements. Furthermore, the Ca2SiO4:Eu3+ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.

Localization-enhanced moiré exciton in twisted transition metal dichalcogenide heterotrilayer superlattices

The stacking of twisted two-dimensional (2D) layered materials has led to the creation of moiré superlattices, which have become a new platform for the study of quantum optics. The strong coupling of moiré superlattices can result in flat minibands that boost electronic interactions and generate interesting strongly correlated states, including unconventional superconductivity, Mott insulating states, and moiré excitons. However, the impact of adjusting and localizing moiré excitons in Van der Waals heterostructures has yet to be explored experimentally. Here, we present experimental evidence of the localization-enhanced moiré excitons in the twisted WSe2/WS2/WSe2 heterotrilayer with type-II band alignments. At low temperatures, we observed multiple excitons splitting in the twisted WSe2/WS2/WSe2 heterotrilayer, which is manifested as multiple sharp emission lines, in stark contrast to the moiré excitonic behavior of the twisted WSe2/WS2 heterobilayer (which has a linewidth 4 times wider). This is due to the enhancement of the two moiré potentials in the twisted heterotrilayer, enabling highly localized moiré excitons at the interface. The confinement effect of moiré potential on moiré excitons is further demonstrated by changes in temperature, laser power, and valley polarization. Our findings offer a new approach for localizing moiré excitons in twist-angle heterostructures, which has the potential for the development of coherent quantum light emitters.

Evolution of Frenkel defect pairs in β-Ga2O3 thin film with the introduction of oxygen and its application in GaN-based ultraviolet light-emitting diode

In this work, β-Ga2O3 thin films were deposited by radio frequency (RF) magnetron sputtering technique. The effect of oxygen-argon flow ratio (OAFR) on the formation of Frenkel defect pairs was systematically analyzed. The Frenkel defect pairs would become abundant when the OAFR was 25:25 sccm, resulting in a severe damage in crystalline quality and an increase in the density of disorder. With the further increase of OAFR, Frenkel defect pairs would dramatically decrease or even vanish due to the significant reduction of oxygen vacancies (V0). Immediately after that, on the basis of avoiding the influence of Frenkel defect pairs inside the β-Ga2O3 films to the devices, the p-NiO/i-Ga2O3/n-GaN diode was fabricated from the as-prepared high-quality β-Ga2O3 film after post-deposition annealing as the electron-blocking layer. Subsequently, its electrical characteristics were investigated in detail which exhibited excellent rectification characteristics under all test temperatures. Correspondingly, the device achieved electroluminescence (EL) with a dominant sharp emission peak in the ultraviolet range (∼375 nm). In the end, the energy band diagram was used for in-depth analysis of the EL mechanism.

Cr:Gd2SrAl2O7: A potential tunable laser crystal with high energy storage capacity

The Cr3+ doped Gd2SrAl2O7 (Cr:GSAO) crystal with tunable light emission has been successfully grown by the Czochralski method for the first time. The Cr:GSAO crystal shows strong absorption on the visible light with an absorption cross-section of 0.53 × 10−19 cm2 at 580 nm for σ-polarization. The crystal field analysis results reveal that Cr3+ ions are accommodated at more than one type of lattice site in GSAO, one with a strong crystal field and the others with an intermediate crystal field. The crystal features long-lived and tunable luminescence. The room temperature luminescence spectrum of Cr:GSAO crystal ranging from 700 nm to 1000 nm is composed of a sharp emission peak and a broad band, which are assigned to the zero-phonon emission and the phonon assisted transitions from 4T2–4A2 of Cr3+. The luminescence lifetime of the Cr:GSAO crystal is 2.82 ms. This indicates that the Cr:GSAO crystal has a potentially good laser performance with excellent energy storage capacity. Our work demonstrates that the Cr:GSAO crystal is a promising candidate for tunable laser gain media.

Solution combustion synthesis of Dy-doped ZnO nanoparticles: An investigation of their structural, optical and photoluminescence characteristics

Undoped and Dy-doped ZnO nanoparticles were synthesized by solution combustion technique using urea as fuel. The synthesized nanoparticles were examined by various characterization tools for their structural, optical and photoluminescence properties. All the nanoparticles are found to possess the hexagonal wurtzite structure of ZnO with crystallite sizes in the range of 16–23 nm. The structural parameters viz. lattice constants, bond lengths, bond angles, and lattice strain of the nanoparticles have been evaluated. The high-resolution transmission electron micrographs and selected area electron diffraction patterns confirm the high crystallinity of the nanoparticles. The optical bandgap estimated from the diffuse reflectance spectra using the Kubelka-Munk method is found to be 2.90 eV for the undoped ZnO. A sharp narrow UV emission peak at ∼396 nm originating from the excitonic recombination is observed in the PL spectra of all the nanoparticles. The visible emission peaks in the PL spectra of undoped ZnO are attributed to different native defects, whereas in Dy-doped ZnO nanoparticles, the visible emissions (blue, yellow and red) are assigned to the 4f intrashell transitions in Dy3+ ions. It has been concluded that the solution combustion synthesized 5 mol% Dy-doped ZnO can be a promising material for white luminescence applications.