Emission Bandwidth Research Articles

Emission bandwidth control on a two-dimensional superlattice microcavity array.

Narrowband thermal emission at high temperatures is required for various thermal energy systems. However, the large lossy energy of refractory metals induces a broad bandwidth emission. Here, we demonstrated a two-dimensional (2D) superlattice microcavity array on refractory metals to control the emission bandwidth. A hybrid resonance mode was obtained by coupling the standing-wave modes and propagating surface-wave modes. The bandwidth emission was controlled by varying the superlattice microcavity array resulting from the change in electric field (E-field) concentration. The quality factor (Q-factor) improved by more than 3 times compared to that of a single-lattice array. A narrower band emission originating from the hybrid mode was observed and analyzed experimentally. This novel surface-relief microstructure method can be used to control the emission bandwidth of thermal emitters used in thermophotovoltaic (TPV) systems and other high-temperature thermal energy systems.

Hydrothermal zinc oxide nanostructures: geometry control and narrow band UV emission

In this work we study zinc oxide nanostructures of various geometries synthesized via the hydrothermal technique on Si (111) substrate. We demonstrate capabilities of the growth protocol for control over the morphology of nanostructures varying from nanowires to hexapods. The obtained samples were studied by photoluminescence spectroscopy to demonstrate a very narrow spontaneous emission near 370 nm. Despite cheap and feasible fabrication, the obtained nanostructures possess high crystallinity confirmed by the absence of typical for ZnO wide emission band in the visible region, related with the structure imperfections. This property together with the capabilities of the geometrical control over the nanostructures unveil perspectives of the reported approach for future UV photonic applications.

Photoluminescence and scintillation of Sn2+-doped gadolinium aluminum-silicate glasses

The photoluminescence and scintillation properties of Sn2+-doped gadolinium aluminum-silicate Gd2O3–Al2O3–SiO2 (GAS) glasses with Si3N4 as reducing agent were investigated. The glasses showed a wide emission band in the range of 360–730 nm due to the relaxation of S1–S0 and T1-S0 of Sn2+ luminescent centers. The luminescent intensity of Sn2+-doped GAS glasses reaches maximum at 0.3 mol% Sn2+. The lifetimes of the glasses vary between 6 and 12 μs, which related to the full width at half maximum (FWHM) of the emission spectra. Different oxides were added to explore the relationship between optical basicity and the luminescent properties of glasses. The addition of B2O3 increases the photoluminescence quantum yield (PL QY) of the glasses, which is due to reduction of the Stokes shift and increment of radiative transition probability in energy level transition. The X-ray induced scintillation luminescence of the glasses were observed and studied.

AlGaN multiple quantum well deep‐ultraviolet micro‐light‐emitting diodes for high color conversion efficiency quantum dots display

AbstractDisplays based on inorganic micro‐light‐emitting diodes (micro‐LEDs) are highly anticipated for next‐generation technologies. AlGaN‐based deep‐ultraviolet (deep‐UV) micro‐LED as the excitation source for quantum dots display with high efficiency was reported in this paper. To achieve optimized electro‐optical performance, deep‐UV micro‐LEDs with different electrodes were fabricated and analyzed in sizes from 200 × 200 to 10 × 10 μm2. At the same forward bias, the devices with Ti/Al‐based electrodes achieved 10 times injection current and three times electroluminescence intensity than those with Cr/Al‐based electrodes. The blueshift phenomenon of deep‐UV light was observed from 292 nm at 2 A/cm2 to 287 nm at 200 A/cm2 with the increasing current density. By the excitation of deep‐UV micro‐LED, quantum dot film achieved high light conversion efficiency and optimized color rendering, as the converted color emission peak was separate from the pumping source. The high energy of deep‐UV photons and the narrow emission bandwidth of QDs resulted in prominent color purity. The forward voltage and electroluminescence intensity uniformity of a 250 × 250 micro‐LED array with each pixel size of 30 × 30 μm2 were further discussed. The optical microscope images of green QD film pumped by a deep‐UV micro‐LED demonstrated its competitive application in the color‐converted display.

Full-Spectrum White Light-Emitting Diodes Enabled by an Efficient Broadband Green-Emitting CaY2ZrScAl3O12:Ce3+ Garnet Phosphor.

Phosphor-containing white light-emitting diodes (LEDs) with low color-correlated temperatures (CCTs) and high color rendering indexes (CRIs) are highly desirable for energy-efficient and environmentally friendly solid-state light sources. Here, we report a new and efficient blue light-excited, green-emitting Ce3+-activated CaY2ZrScAl3O12 phosphor, which underpins the fabrication of high-color quality and full-visible-spectrum warm-white LED devices with ultrahigh CRI values (Ra > 96 and R9 > 96). A family of CaY2ZrScAl3O12:Ce3+ phosphors with different Ce3+ dopant concentrations were prepared by high-temperature solid-state synthesis. X-ray diffraction and corresponding Rietveld refinement reveal a garnet structure with an Ia3̅d space group and crystallographic parameters a = b = c = 12.39645(8) Å, α = β = γ = 90°, and V = 1904.99(4) Å3. Luminescence properties were studied in detail as a function of Ce3+ with the optimal concentration 1% mol. Impressively, CaY2ZrScAl3O12:1%Ce3+ exhibits a broad excitation band from 370 to 500 nm, peaking at ∼421 nm, which is well matched with emission from commercial blue LED chips. Under 421 nm excitation, the CaY2ZrScAl3O12:1%Ce3+ phosphor produces dazzling green light in a wide emission band from 435 to 750 nm (emission peak: 514 nm; full width at half-maximum: 113 nm), with a high internal quantum efficiency of 63.1% and good resistance to thermal quenching (activation energy of 0.28 eV). A white LED device combining a 450 nm blue LED chip with CaY2ZrScAl3O12:1%Ce3+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor as color converters demonstrates bright warm-white light with excellent CIE color coordinates of (0.3938, 0.3819), low CCT of 3696 K, high CRI (Ra = 96.9, R9 = 98.2), and high luminous efficacy of 45.04 lm W-1 under a 20 mA driving current. New green phosphors enable the design and implementation of efficient luminescent materials for healthy solid-state lighting.

A high absorption efficiency blue-emitting phosphor NaSrScSi2O7:Eu2+ for near-UV-pumped white light-emitting diodes

The Eu2+ ion is extensively used as an activator due to its wide excitation band and high efficiency emission spectrum. However, most Eu2+-activated blue-emitting phosphors have low absorption efficiency in the near-ultraviolet (n-UV) region or lack the short-wavelength blue light emission (<450 nm), resulting in UV light leakage or poor color rendering. Herein, we have successfully prepared a brand-new blue phosphor NaSrScSi2O7: Eu2+ by solid-state reaction method. The Rietveld refinement of the powder diffraction data, luminescent properties, decay lifetime, quantum efficiencyand thermal quenching have been investigated in detail. Under 345 nm excitation, the NaSrScSi2O7: 0.03Eu2+phosphor manifests an asymmetric emission spectrum centered at 427 nm, and notably, shows a high absorption efficiency of 84.35%. Finally, we encapsulated two white light-emitting diodes (WLEDs) devices using as-prepared blue-emitting phosphor and three commercial phosphors. At 80 mA drive current, both packaged devices demonstrate warm white light. Meanwhile, the WLED-2 with NaSrScSi2O7: 0.03Eu2+ blue-emitting phosphor has a lower correlated color temperature of 3726 K, its spectrum complements more short-wavelength spectrum, and the special color rendering index R6 and R7 increased from 95.2, 94.5 to 98.3, 96.5, respectively, compared with WLED-1 without present phosphor. These results demonstrate that NaSrScSi2O7: Eu2+ blue-emitting phosphor is a prospective novel luminescent material for WLEDs.

Ni2+-Doped Garnet Solid-Solution Phosphor-Converted Broadband Shortwave Infrared Light-Emitting Diodes toward Spectroscopy Application.

Broadband shortwave infrared (SWIR) light-emitting diodes (LEDs), capable of advancing the next-generation solid-state smart invisible lighting technology, have sparked tremendous interest and will launch ground-breaking spectroscopy and instrumental applications. Nevertheless, the device performance is still suppressed by the low quantum efficiency and limited emission bandwidth of the critical phosphor layer. Herein, we report a high-performance Ni2+-doped garnet solid-solution broadband SWIR emitter centered at ∼1450 nm with a large full-width at half-maximum of ∼300 nm, thereby fabricating, for the first time, a directly excited Ni2+-doped garnet solid-solution phosphor-converted broadband SWIR LED device. A synergetic enhancement strategy, adding a fluxing agent and a charge compensator simultaneously, is proposed to deliver a more than 20-fold increase of the SWIR emission intensity and nearly 2-fold improvement of the thermal quenching behavior. The site occupation and mechanism behind the synergetic enhancement strategy are elucidated by a combination of experimental study and theoretical calculation. A prototype of the SWIR LED with a radiation flux of 1.25 mW is fabricated and utilized as an invisible SWIR light source to demonstrate the SWIR spectroscopy applications. This work not only opens a window to explore novel broadband SWIR phosphors but also provides a synergetic strategy to remarkably improve the performance of artificial SWIR LED light sources.

High-quantum yield alloy-typed core/shell CdSeZnS/ZnS quantum dots for bio-applications

BackgroundQuantum dots (QDs) have been used as fluorophores in various imaging fields owing to their strong fluorescent intensity, high quantum yield (QY), and narrow emission bandwidth. However, the application of QDs to bio-imaging is limited because the QY of QDs decreases substantially during the surface modification step for bio-application.ResultsIn this study, we fabricated alloy-typed core/shell CdSeZnS/ZnS quantum dots (alloy QDs) that showed higher quantum yield and stability during the surface modification for hydrophilization compared with conventional CdSe/CdS/ZnS multilayer quantum dots (MQDs). The structure of the alloy QDs was confirmed using time-of-flight medium-energy ion scattering spectroscopy. The alloy QDs exhibited strong fluorescence and a high QY of 98.0%. After hydrophilic surface modification, the alloy QDs exhibited a QY of 84.7%, which is 1.5 times higher than that of MQDs. The QY was 77.8% after the alloy QDs were conjugated with folic acid (FA). Alloy QDs and MQDs, after conjugation with FA, were successfully used for targeting human KB cells. The alloy QDs exhibited a stronger fluorescence signal than MQD; these signals were retained in the popliteal lymph node area for 24 h.ConclusionThe alloy QDs maintained a higher QY in hydrophilization for biological applications than MQDs. And also, alloy QDs showed the potential as nanoprobes for highly sensitive bioimaging analysis.Graphical

“Turn-on” fluorescence probe for Al (III) and Hg (II) ions in aqueous medium: Synthesis, characterization, cytotoxicity, visual results in solution and cancer cells

In this study, An efficient OFF–ON fluorescent compound integrated with nitrobenzofurazan and phenolphthalein (NBFP) has been prepared for the detection of metals ions. NBFP was characterized with 1H NMR, 13C NMR, COSY-NMR, FTIR, and Mass spectrometry. The fluorescent response towards metal ions displayed that NBFP is selective for Hg (II) and Al (III), with a detection limit of 14.7 µM and 16.3 µM for Hg(II) and Al(III), respectively. Job’s plot for NBFP + Hg (II) complex, and NBFP + Al (III) complex confirmed the 1:2 ligand–metal stoichiometry. Binding constant (Ksv) from Stern-Volmer equation was found to be 1.60 × 102 M−1 for NBFP + Hg (II) complex and 9.25 × 102 M−1 for NBFP + Al (III) complex respectively, indicating a strong interaction between ligand and selective metal ions in the presence of other ions. The quantum yield of NBFP was found to be ΦL = 0.028, exhibiting a weak and wide emission band. Cytotoxicity of NBFP has been evaluated before application in living cell fluorescent imaging for the detection of metal ions. The result showed that NBFP exhibits good biocompatibility in living cells and displayed a good response for the detection of Al (III) and Hg (II) ions in living cells using the confocal microscope.

Highly efficient broadband white-light emission in two-dimensional semi-conductive hybrid lead chlorides.

White-light emission (WLE) materials based on organic-inorganic hybrid lead halides have drawn considerable attention because of their applications in light-emission equipment. Despite considerable efforts, there is still a lack of two-dimensional (2D) lead-chlorine white-light emitting halides with high photoluminescence quantum efficiency (PLQE). Herein, we report the preparation of a new 2D layered hybrid halide, [DTHPE]Pb4Cl10, which exhibits bright wide-band WLE, a high PLQE of 8.86% and high anti-water stability. To the best of our knowledge, the PLQE of [DTHPE]Pb4Cl10 exceeds that of most 2D lead chlorides. Furthermore, the emission intensity is unchanged even after continuous immersion in water for 7 days. Photoluminescence measurements indicate that the WLE originates from self-trapped excitons. [DTHPE]Pb4Cl10 is a promising visible-blind UV hybrid halide owing to its excellent photoelectric response. [DTHPE]Pb4Cl10 is an effective white-light emitting material for display applications. The coexistence of a high performance visible-blind UV response and high efficiency white-light emission provides attractive possibilities for potential applications in the multifunctional photoelectronic field.

Analysis of luminescence decay dynamics in metal-dielectric photonic structures with organic layers

Metal-dielectric photonic structures with organic materials 4,4-bis(N-carbazolyl)-1,1-biphenyl and 4,4'-bis[4-(di-ptolylamino)styryl]biphenyl) as light emitting layers were investigated. The formation of the polaritonic modes in the investigated structures was experimentally demonstrated and a correlation between theoretical and experimental dispersion was shown. Was shown, that increase in interaction between organic exciton and optical mode leads to a significant decrease in the lower polariton emission bandwidth. Keywords: light-emitting layers, exciton, luminescence.

Recent progress of single-halide perovskite nanocrystals for advanced displays.

Light-emitting diodes based on lead halide perovskite nanocrystals (LHP NCs) have shown an astonishing increase in efficiency in just several years of academic research, reaching high external quantum efficiencies exceeding 20%. The extensive color-tunability and narrow emission bandwidth of LHP NCs, in particular, are of great importance in the creation of the next generation of ultra-high-definition displays, as defined by the Rec. 2020 standard recommendation. In fact, whereas the colour of LHP NCs can be easily tuned by the compositions of halogens, the ion migration in mixed-halide perovskites under the electric field will seriously affect the spectral stability and operational lifetimes of perovskite light-emitting diodes (PeLEDs). Therefore, it is essential to realize efficient colour-saturated PeLEDs based on single-halide perovskite NCs. In this review, we focus on the recent progress in LHP NC-based PeLEDs and highlight the strategy of tuning the spectral emission based on quantum confinement or cation alloying/doping in single-halide perovskite NCs. Finally, we will give an outlook on future research avenues for preparing high-efficiency pure green, red and blue PeLEDs based on single-halide perovskite NCs.

Surface ligand engineering of perovskite nanocrystals with a conjugated sulfonate ligand for light-emitting applications

PeLEDs based on SβSS-modified CsPbBr3 NCs showed a bright green electroluminescence and a narrow emission bandwidth.

Анализ динамики затухания люминесценции в металл-диэлектрических фотонных структурах с органическими слоями

Metal-dielectric photonic structures with organic materials 4,4-bis(N-carbazolyl)-1,1-biphenyl and 4,4′-bis[4-(di-ptolylamino)styryl] biphenyl) as light emitting layers were investigated. The formation of the polaritonic modes in the investigated structures was experimentally demonstrated and a correlation between theoretical and experimental dispersion was shown. Was shown, that increase in interaction between organic exciton and optical mode leads to a significant decrease in the lower polariton emission bandwidth.

Waste to white light: a sustainable method for converting biohazardous waste to broadband white LEDs.

The Covid-19 pandemic has generated a lot of non-degradable biohazardous plastic waste across the globe in the form of disposable surgical and N95 masks, gloves, face shields, syringes, bottles and plastic storage containers. In the present work we address this problem by recycling plastic waste to single system white light emitting carbon dots (CDs) using a pyrolytic method. The synthesized CDs have been embedded into a transparent polymer to form a carbon dot phosphor. This CD phosphor has a broad emission bandwidth of 205 nm and is stable against photo degradation for about a year. A white LED with CRI ∼70 and CIE co-ordinates of (0.25, 0.32) using the fabricated CD phosphor is reported. Further our phosphor is scalable and is environmentally sustainable, and will find wide application in next generation artificial lighting systems.

Narrow‐bandwidth emissive carbon dots: A rising star in the fluorescent material family

AbstractFluorescent carbon dots (CDs) have recently become a research hotspot in multidisciplinary fields owing to their distinctive advantages, including outstanding photoluminescence properties, high biocompatibility, low toxicity, and abundant raw materials. Among the promising CDs, narrow‐bandwidth emissive CDs with high color purity have emerged as a rising star in recent years because of their significant potential applications in bioimaging, information sensing, and photoelectric displays. In this review, the state‐of‐the‐art advances of narrow‐bandwidth emissive CDs are systematically summarized, and the factors influencing the emission bandwidth, preparation methods, and applications of narrow‐bandwidth emissive CDs are described in detail. Besides, existing challenges and future perspectives for achieving high‐performance narrow‐bandwidth emissive CDs are also discussed. This overview paper is expected to generate more interest and promote the rapid development of this significant research area.

Distributed Kerr Lens Mode-Locked Yb:YAG Thin-Disk Oscillator

Ultrafast laser oscillators are indispensable tools for diverse applications in scientific research and industry. When the phases of the longitudinal laser cavity modes are locked, pulses as short as a few femtoseconds can be generated. As most high-power oscillators are based on narrow-bandwidth materials, the achievable duration for high-power output is usually limited. Here, we present a distributed Kerr lens mode-locked Yb:YAG thin-disk oscillator which generates sub-50 fs pulses with spectral widths far broader than the emission bandwidth of the gain medium at full width at half maximum. Simulations were also carried out, indicating good qualitative agreement with the experimental results. Our proof-of-concept study shows that this new mode-locking technique is pulse energy and average power scalable and applicable to other types of gain media, which may lead to new records in the generation of ultrashort pulses.

Luminescence of Ti-Sapphire coatings prepared by plasma electrolytic oxidation and their application in temperature sensing

15 µm thick Ti-Sapphire coatings were synthesised at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominant is the alpha phase of alumina with the small presence of the gamma phase. The estimated average crystalline size is 41 nm. Ti is uniformly distributed in these polycrystalline ceramic coatings and does not affect morphology or phase content. Photoluminescence of PEO-created coatings shows typical absorption, excitation, and emission features of Ti-Sapphire with two broad-overlapping excitation bands in the green and blue spectral region due to the Jahn-Teller splitting of the 2Eg level and the Stokes shifted emission centred at 720 nm. 2Eg energy state splitting is equal to 2195 cm−1 and 10 Dq ≈ 19,300 cm−1. The highest emission intensity was observed in the coating prepared with the 0.1 g/L TiO2 powder concentration, i.e. 0.32 at% of incorporated Ti3+. Emission spectra recorded at temperatures ranging from 100 K to 300 K revealed the Mott-Seitz temperature dependence of emission intensity with the 1180 cm−1 activation energy. The fit to the McCumber-Sturge relation gave, for the first time, the value of Debye temperature of 594 K of Al2O3:Ti. Non-contact, luminescence temperature sensing from the temperature-induced changes in the emission bandwidth gave a high sensitivity of 3.2 cm−1 K−1 and 0.19 K temperature resolution. The PEO created Ti-sapphire coatings are a promising multifunctional barrier level – optical temperature sensor material for applications in harsh environments or on large aluminium surfaces. It shows potential to be used as a planar waveguide Ti-Sapphire laser active medium.

Doped organic charge-transfer cocrystal with tunable fluorescence of wide band emission

Supramolecular crystals with tunable fluorescence emission have been demonstrated for many applications. Guided by quantum chemical calculations, a series of (TCNB)x(OFN)1-x(Cor) doped cocrystals were synthesized by charge transfer induced self-assembly with coronene (Cor) as electron donor and octafluoronaphthalene (OFN) or 1,2,4,5-tetracyanobenzene (TCNB) as electron acceptors. Structural similarity between OFN-Cor and TCNB-Cor are necessary for full proportion doping of (TCNB)x(OFN)1-x(Cor). Based on experimental and theoretical analysis, doped cocrystals can be tuned in photophysical properties (luminescent color, fluorescence lifetime, quantum yield). With the doping ratio increasing, the doped cocrystals emit fluorescent in different colors from blue to yellow and then to orange. Through molecular design to select and synthesize organic fluorescent materials is an efficient strategy to deeply understand their structure–activity relationship, which pave a potential path to develop novel functional supramolecular systems.

Metallo-dielectric metasurfaces for thermal emission with controlled spectral bandwidth and angular aperture

We introduce thermal metallo-dielectric metasurfaces as mid IR sources. The emitter is a lossy metal. The spectral and angular emission is controlled using a periodic array of high refractive dielectric resonators. We introduce a design that allows to control independently the emission bandwidth and the angular aperture while ensuring a large emissivity. To validate the concept, we fabricated and characterized a metasurface, showing a good agreement with the theory.