Narrow Photoluminescence Band Research Articles

Eu2+ doped cesium alkaline earth chloride nanocrystals in glass for X-ray imaging

High-performance and low-cost metal halide perovskite scintillator materials have important applications in X-ray detection and imaging. However, large-sized perovskite scintillator panel with high transmittance, low toxicity and long-term stability is still lacking. Herein, Eu2+ doped cesium alkaline earth chloride nanocrystals (Eu2+: CsCaCl3, Eu2+: CsSrCl3, and Eu2+: Cs2BaCl4 NCs) embedded in glasses through conventional melt-quenching and subsequent heat-treatment were developed. These NCs doped glasses exhibited highly efficient and narrowband photoluminescence in blue region. Benefitting from the large X-ray absorption coefficient and high photoluminescence quantum yied, these Eu2+: CsCaCl3 NCs doped glass scintillator shows light yield of ∼9300 photons/MeV, detection limit of ∼213.8 μGy/s, and spatial resolution of 30.0 lp/mm. These results demonstrated that glasses containing Eu2+ doped cesium alkaline earth chloride nanocrystals are promising for X-ray detection and imaging.

Formation of Ge-V color centers in poly- and monocrystalline CVD diamond: A comparative study

Germanium-Vacancy (Ge-V) color centers in diamond have narrow-band photoluminescence (PL) at room temperature (RT) and attract considerable attention due to their possible application in quantum information technologies, biomedicine, and local optical thermometry. In this work, we used microwave plasma chemical vapor deposition (MPCVD) to synthesize Ge-doped polycrystalline diamond (PCD) films and single-crystal diamond (SCD) epitaxial layers in hydrogen-methane-germane gas mixtures. Thick (>100 μm) layers of both types were grown to analyze their structure and luminescence characteristics. The first demonstration of the absorption of Ge-V centers in both PCD and SCD materials at low temperatures is presented. The sufficient narrowing of the Ge-V PL line for the SCD sample in comparison with the PCD sample was observed. On the other hand, the intensity of the Ge-V signal was an order of magnitude higher in the PCD sample compared to the SCD sample. A set of single Ge-V centers formed during CVD has been demonstrated. The results obtained can be used to manufacture and design various photonic devices based on Ge-V color centers.

Composition-Dependent Optical Properties of Cu–Zn–In–Se Colloidal Nanocrystals Synthesized via Cation Exchange

Copper chalcogenide-based nanocrystals (NCs) are a suitable replacement for toxic Cd/Pb chalcogenide-based NCs in a wide range of applications including photovoltaics, optoelectronics, and biological imaging. However, despite rigorous research, direct synthesis approaches of this class of compounds suffer from inhomogeneous size, shape, and composition of the NC ensembles, which is reflected in their broad photoluminescence (PL) bandwidths. A partial cation exchange (CE) strategy, wherein host cations in the initial binary copper chalcogenide are replaced by incoming cations to form ternary/quaternary multicomponent NCs, has been proven to be instrumental in achieving better size, shape, and composition control to this class of nanomaterials. Additionally, adopting synthetic strategies which help to eliminate inhomogeneities in the NC ensembles can lead to narrower PL bandwidths, as was shown by single-particle studies on I–III–VI2-based semiconductor NCs. In this work, we formulate a two-step colloidal synthesis of Cu–Zn–In–Se (CZISe) NCs via a partial CE pathway. The first step is the synthesis of Cu2–xSe NCs, which serve as a template for the subsequent CE reaction. The second step is the incorporation of the In3+ and Zn2+ guest cations into the synthesized Cu2–xSe NCs via simultaneous injection of both metal precursors, which results in gradient-alloyed CZISe NCs with a Zn-rich surface. The as-synthesized NCs exhibit near-infrared (NIR) PL without an additional shell growth, which is typically required in most of the developed protocols. The photoluminescence quantum yield (PLQY) of these Cu chalcogenide-based NCs reaches 20%. These NCs also exhibit intriguingly narrow PL bands, which challenges the notion of broad PL bands being an inherent property of this class of NCs. Additionally, a variation in the feed ratios of the incoming cations, i.e., In/Zn, results in the variation of the composition of the synthesized NCs. Henceforth, the optical properties of these NCs could be tuned by a simple variation of the composition of the NCs achieved by varying the feed ratios of the incoming cations. Within a narrow size distribution, the PL maxima range from 980 to 1060 nm, depending on the composition of the NCs. Post-synthetic surface modification of the synthesized NCs enabled the replacement of the parent long-chain organic ligands with smaller species, which is essential for their prospective applications requiring efficient charge transport. With PL emission extended into the NIR, the synthesized NCs are suitable for an array of potential applications, most importantly in the area of solar energy harvesting and bioimaging. The large Stokes shift inherent to these materials, their absorption in the solar range, and their NIR PL within the biological window make them suitable candidates.

Luminescence mechanisms in the 2V2O5–xLi2O–(98 − x)B2O3 glass matrices developed for creation of glass–ceramic materials

The oxide glass–ceramics is a promising class of solid state materials because they are using thermally stable and chemically inert glass oxide matrices. Development of such efficient glass matrices suitable for creation of glass–ceramic materials for several purposes is an important practical task. The xLi2O–yV2O5–(100 − x − y)B2O3 undoped glass and 47Li2O–2V2O5–50B2O3–1La0.3Eu0.7VO4 glass samples with crystalline nanoinclusions were synthesized and investigated using XRD, IR and UV–Vis spectroscopy and UV band-to-band excitation of luminescence. The synthesized glass samples are characterized by wide band photoluminescence emission with maximum at 570 nm and intensity increased with increase of Li2O concentration. The excitation spectra consist of three bands with maxima located at 270, 320 and 365 nm. The observed concentration dependencies of spectral distributions in the absorption and excitation spectra are explained by influence of the lithium ions on a ratio between triborate and tetraborate groups in the glass networks. The assumption is made that the observed wide band photoluminescence emission of the glass matrix can appear as a result of recombination processes between the defects in borate networks and the broken vanadate groups. The crystalline component in the doped glass samples is found to not affect the luminescence properties of the glass matrix. Intensity of narrow band photoluminescence emission of the crystalline component is up to 10 times more intense than that of the glass matrix wide band emission. The synthesized type of the glass matrices has promising characteristics for the use of developed materials in lighting devices, as it allows improving the spectral distribution of light emission towards the white light.

High-efficiency narrow-band blue emission from lead-doped Cs2ZnBr4 nanocrystals

All-inorganic metal halide nanocrystals (NCs) with high-efficiency narrow-band photoluminescence (PL) are highly desirable for display applications. Herein, we report a strategy to achieve efficient narrow-band blue PL in 0D Cs2ZnBr4 NCs via minor Pb2+ doping. Upon doping with 0.1 mol% Pb2+, the intrinsically non-luminescent Cs2ZnBr4 NCs become efficiently luminescent, with a sharp emission peak at 433 nm (full-width at half maximum of ≈10.2 nm) and a high quantum yield of 82.9 %. With the aid of the first-principles calculations, we unveil that the narrow-band blue PL originates from the localized exciton emission arising from the peculiar electronic band structure induced by Pb2+ doping, in which the photogenerated excitons in [PbBr4]2− tetrahedra are trapped and localized within [ZnBr4]2− tetrahedra. Furthermore, by control of the Pb2+ concentration (0.1–3.0 mol%), we achieve dual-band-tunable blue/green PL in Cs2ZnBr4: Pb2+/CsPbBr3 hybrid NCs with high efficiency and signifcantly improved stability compared to that of bare CsPbBr3. These findings provide a unique approach to achieve highly efficient narrow-band PL in metal halide NCs via minor Pb2+ doping, which largely mitigates the toxicity concern about lead halide perovskites and thus may open up new opportunities for the materials design and device engineering in practical applications.

Large-area waterproof and durable perovskite luminescent textiles

Lead halide perovskites show great potential to be used in wearable optoelectronics. However, obstacles for real applications lie in their instability under light, moisture and temperature stress, noxious lead ions leakage and difficulties in fabricating uniform luminescent textiles at large scale and high production rates. Overcoming these obstacles, we report simple, high-throughput electrospinning of large-area (> 375 cm2) flexible perovskite luminescent textiles woven by ultra-stable polymer@perovskite@cyclodextrin@silane composite fibers. These textiles exhibit bright and narrow-band photoluminescence (a photoluminescence quantum yield of 49.7%, full-width at half-maximum <17 nm) and the time to reach 50% photoluminescence of 14,193 h under ambient conditions, showcasing good stability against water immersion (> 3300 h), ultraviolet irradiation, high temperatures (up to 250 °C) and pressure surge (up to 30 MPa). The waterproof PLTs withstood fierce water scouring without any detectable leaching of lead ions. These low-cost and scalable woven PLTs enable breakthrough application in marine rescue.

CsPbBr3 nanocrystal-embedded glasses for luminescent solar concentrators

Luminescent solar concentrators (LSCs) have important application in building integrated photovoltaic. CsPbX3 (X = Cl, Br, I) perovskite nanocrystals possessing tunable band gap energies, large absorption coefficients, narrow band photoluminescence (PL), and high photoluminescence quantum yield (PL QY), have great potential application in LSCs. However, instability of perovskite nanocrystals in ambient environment still limits their practical application. Herein, as a proof-of-concept experiment, CsPbBr3 nanocrystal-embedded glass sheets with various geometric factors are investigated as LSCs. Due to the wide absorption spectral range, high PL QY, and narrow PL, optical efficiency of 6.17% (2 × 2 cm2) is achieved from LSCs based on CsPbBr3 nanocrystal-embedded glass sheets. Importantly, the stability tests show that the glass matrix can effectively protect CsPbBr3 nanocrystals from eroding of ambient environment. These results show that CsPbBr3 nanocrystal-embedded glasses are promising materials for LSCs.

Photochromic switching of narrow-band lattice resonances.

Narrow-band resonances supported by a variety of periodic metallic or dielectric nanostructures have great potential applications in light sources, optical sensors, and switches or modulators. Here we report the switching of narrow-band lattice resonances in a mirror-backed two-dimensional array of dielectric nanopillars. The nanopillar is composed of a silica core and photochromic coating. By exposure to ultraviolet light, the photochromic molecules can be turned into a state that is highly absorptive around the wavelength of the lattice resonance. Because the lattice resonance has enhanced the near-fields concentrated on the tops of dielectric nanopillars, the absorptive coating can destroy this resonance. The absorptive state of the photochromic molecules can be recovered to a transparent state by exposure to visible light. We fabricate the device and characterize the change of reflection spectra to demonstrate the reversible switching of lattice resonances by exposure to ultraviolet and visible light alternately. An all-optical control of the narrow-band photoluminescence is further demonstrated by combining a fluorescent dye with the photochromic molecules.

Liquid-phase sintering of lead halide perovskites and metal-organic framework glasses.

Lead halide perovskite (LHP) semiconductors show exceptional optoelectronic properties. Barriers for their applications, however, lie in their polymorphism, instability to polar solvents, phase segregation, and susceptibility to the leaching of lead ions. We report a family of scalable composites fabricated through liquid-phase sintering of LHPs and metal-organic framework glasses. The glass acts as a matrix for LHPs, effectively stabilizing nonequilibrium perovskite phases through interfacial interactions. These interactions also passivate LHP surface defects and impart bright, narrow-band photoluminescence with a wide gamut for creating white light-emitting diodes (LEDs). The processable composites show high stability against immersion in water and organic solvents as well as exposure to heat, light, air, and ambient humidity. These properties, together with their lead self-sequestration capability, can enable breakthrough applications for LHPs.

Enhanced Room-Temperature Photoluminescence Quantum Yield in Morphology Controlled J-Aggregates.

Supramolecular assemblies from organic dyes forming J‐aggregates are known to exhibit narrowband photoluminescence with full‐width at half maximum of ≈9 nm (260 cm−1). Applications of these high color purity emitters, however, are hampered by the rather low photoluminescence quantum yields reported for cyanine J‐aggregates, even when formed in solution. Here, it is demonstrated that cyanine J‐aggregates can reach an order of magnitude higher photoluminescence quantum yield (increase from 5% to 60%) in blend solutions of water and alkylamines at room temperature. By means of time‐resolved photoluminescence studies, an increase in the exciton lifetime as a result of the suppression of non‐radiative processes is shown. Small‐angle neutron scattering studies suggest a necessary condition for the formation of such highly emissive J‐aggregates: the presence of a sharp water/amine interface for J‐aggregate assembly and the coexistence of nanoscale‐sized water and amine domains to restrict the J‐aggregate size and solubilize monomers, respectively.

Фотолюминесценция композитов полиметилметакрилат / [(Zn,Cd)S : Mn,Cu,Eu

Nanoscale structures based on zinc and cadmium sulfides doped with Mn, Cu, and Eu ions were synthesized by the method of emerging reagents in a polymerizing medium of methyl methacrylate. The broadband photoluminescence of the compositions is associated with recombination processes at the defect levels of semiconductor structures. Narrow photoluminescence bands occur during electron transitions between the energy levels of Eu3+ ions. The excitation of photoluminescence occurs as a result of the interband transition and electron transitions to the levels of structural defects, as well as during self-absorption and energy transfer to the levels of Eu3+ ions.

Improving Photoluminescence Quantum Yield of CdTe Quantum Dots Using a Binary Solvent (Water + Glycerin) in the One-Pot Approach Synthesis

The present work describes the comparison of the optical and structural properties between CdTe quantum dots (QD) synthesized in water and in the binary solvent (water + glycerin) via one-pot approach synthesis. The optical properties of the nanocrystals obtained with different synthesis parameters were characterized by UV-visible and photoluminescence spectroscopies. The structural chracterization were performed by Fourier transform infrared spectroscopy (FTIR), zeta potential, size-distribution by dynamic light scattering (DLS), X-ray diffraction (XRD), and also by high-resolution transmission electron microscopy (HRTEM). The optical properties of CdTe QD when synthesized in the binary solvent were better, resulting in the increase of photoluminescence quantum yield (φƒ). The CdTe QD prepared in 120 min, at pH 10.0, in the Cd:Te molar ratio 20:1, using the molar ratio 1:1.5 of Cd:TGA (thioglycolic acid), exhibited a narrow photoluminescence band and enhanced φƒ for the samples synthesized in a binary solvent in comparison to water solvent (58.4 and 49.5%, respectively).

Achieving Matrix Quantum Dot Light-Emitting Display Based on All-Inorganic CsPbBr₃ Perovskite Nanocrystal Composites

We present a display consisting of a 64-cell quantum dot (QD) light-emitting diodes (LEDs) array manufactured by spin coating and steel plate design evaporation technology. The QDLED pixels in the array can be driven independently. The surface of perovskite nanocrystal (NC) composite was modified by using pure natural material aloe-vera gel as the organic precursor to obtain high-quality narrow band photoluminescence emission all-inorganic CsPbBr3 perovskite NC composites. Here, an open-source Arduino microcontroller unit was used as the dynamic micro-control terminal, combined with a step-down module and four motor drive modules to make the display driver circuit. Finally, a 99% operating rate and a maximum brightness of 3366 cd $\text{m}^{-2}$ were achieved in the 8 $\times $ 8 perovskite QDLEDs array display. Furthermore, an electroluminescence dynamic pattern display based on a 64-cell QDLEDs array display has been successfully demonstrated. This study demonstrates the potential of perovskite devices for next-generation displays.

Microscopic lattice for two-dimensional dipolar excitons

We report a two-dimensional artificial lattice for dipolar excitons confined in a GaAs double quantum well. Exploring the regime of large fillings per lattice site, we verify that the lattice depth competes with the magnitude of excitons repulsive dipolar interactions to control the degree of localisation in the lattice potential. Moreover, we show that dipolar excitons radiate a narrow-band photoluminescence, with a spectral width of a few hundreds of micro-eV at 340 mK, in both localised and delocalised regimes. This makes our device suitable for explorations of dipolar excitons quasi-condensation in a periodic potential.

Engineering Edge States of Graphene Nanoribbons for Narrow-Band Photoluminescence.

Solid-state narrow-band light emitters are on-demand for quantum optoelectronics. Current approaches based on defect engineering in low-dimensional materials usually introduce a broad range of emission centers. Here, we report narrow-band light emission from covalent heterostructures fused to the edges of graphene nanoribbons (GNRs) by controllable on-surface reactions from molecular precursors. Two types of heterojunction (HJ) states are realized by sequentially synthesizing GNRs and graphene nanodots (GNDs) and then coupling them together. HJs between armchair GNDs and armchair edges of the GNR are coherent and give rise to narrow-band photoluminescence. In contrast, HJs between the armchair GNDs and the zigzag ends of GNRs are defective and give rise to nonradiative states near the Fermi level. At low temperatures, sharp photoluminescence emissions with peak energy range from 2.03 to 2.08 eV and line widths of 2-5 meV are observed. The radiative HJ states are uniform, and the optical transition energy is controlled by the band gaps of GNRs and GNDs. As these HJs can be synthesized in a large quantity with atomic precision, this finding highlights a route to programmable and deterministic creation of quantum light emitters.

Hybrid halobismuthates as prospective light-harvesting materials: Synthesis, crystal, optical properties and electronic structure

In the present paper, the synthesis, X-ray structural characterization, optical properties and electronic structures of three novel organic–inorganic hybrid compounds of the general formula [CH3SC(NH2)2]xBiAx+3, (A = I, Br, Cl, and x = 1 or 2) are reported. All of them show intense narrow excitonic peaks at the absorption spectra and narrow photoluminescence bands. In the case of (x = 1 and A = I) its structure consists of edge sharing BiI6 octahedral forming zigzag chains and in the case of (x = 2 and A = Br, Cl) their structure consists of corner sharing BiX6 octahedral also forming zigzag chains. The amine group is located in the free cavities between the chains. Their structural, optical and vibronic properties were studied. Band structure calculations were made in order to compare the results with the experimental findings and gain an insight of the properties of these new compounds.

Optical properties of CsPbCl3 nanocrystals in phosphate glass

CsPbCl3 nanocrystals embedded glasses have potential to incorporate transition metal ions and lead to efficient spectral conversion for applications as solar concentrator materials in building. Here, CsPbCl3 nanocrystals were precipitated through heat-treatment in phosphate glasses with potential application in building. X-ray diffraction patterns confirm that CsPbCl3 nanocrystals were formed in glasses. By changing the heat-treatment conditions, absorption peaks of the CsPbCl3 nanocrystals can be tuned from 3.06 eV (405 nm) to 3.25 eV (381 nm). Upon 255–325 nm UV light excitation, photoluminescence in the range of 350–530 nm was observed. Upon 325–375 nm UV light excitation, CsPbCl3 nanocrystals exhibited narrow band photoluminescence centering at 405–410 nm with Stokes shift almost linearly dependent on the band gap energy of CsPbCl3 nanocrystals.

Hydrophobic Metal Halide Perovskites for Visible-Light Photoredox C-C Bond Cleavage and Dehydrogenation Catalysis.

Two-dimensional lead and tin halide perovskites were prepared by intercalating the long alkyl group 1-hexadecylammonium (HDA) between the inorganic layers. We observed visible-light absorption, narrow-band photoluminescence, and nanosecond photoexcited lifetimes in these perovskites. Owing to their hydrophobicity and stability even in humid air, we applied these perovskites in the decarboxylation and dehydrogenation of indoline-2-carboxylic acids. (HDA)2 PbI4 or (HDA)2 SnI4 were investigated as photoredox catalysts for these reactions, and quantitative conversion and high yields were observed with the former.

Growth of polycrystalline and single-crystal CVD diamonds with bright photoluminescence of Ge-V color centers using germane GeH4 as the dopant source

Germanium-Vacancy (Ge-V) color center in diamond possesses a narrow band photoluminescence (PL) emission in the orange spectral range interesting as a single-photon source for quantum optical technologies and thermometry, therefore, development of methods for the controllable doping of diamond with Ge is of high importance for such applications. Here, we report on the synthesis of polycrystalline and epitaxial single crystal Ge-doped films using microwave plasma chemical vapor deposition (CVD) technique by addition of the germane GeH4 gas into the H2-CH4 plasma. It is demonstrated, that GeH4 addition affects the CVD growth of microcrystalline diamond, reducing the film growth rate and increasing the average diamond grain size. The films show bright photoluminescence of Ge-V centers at ≈602 nm under the optimized GeH4 concentration, with a zero-phonon line width of 1.6 nm (FWHM) for Ge-V ensemble at low temperatures (5 K). The developed in-situ doping from the germane gas opens a way for a better control of the Ge-V color center formation in diamond for photonic applications.

Narrow band-edge photoluminescence from AgInS2 semiconductor nanoparticles by the formation of amorphous III\u2013VI semiconductor shells

Nanoparticles of I–III–VI semiconductors are promising candidates for novel non-toxic fluorescent materials. However, removal of defect levels responsible for their broad-band emission has not been successful to date. The present study demonstrates, for the first time, the coating of core AgInS2 nanoparticles—one of the I–III–VI group semiconductors with a bandgap in the visible region—with III–VI group semiconductors. The AgInS2/InSx and AgInS2/GaSx (x = 0.8–1.5) core/shell structures generate intense narrow-band photoluminescence originating from a band-edge transition at a wavelength shorter than that of the original defect emission. Microscopic analyses reveal that the GaSx shell has an amorphous nature, which is unexpected for typical shell materials such as crystalline lattice-matching ZnS. Single-particle spectroscopy shows that the average linewidth of the band-edge photoluminescence is as small as 80.0 meV (or 24 nm), which is comparable with that of industry-standard II–VI semiconductor quantum dots. In terms of photoluminescence quantum yield, a value of 56% with nearly single-band emission has been achieved as a result of several modifications to the reaction conditions and post-treatment to the core/shell nanoparticles. This work indicates the increasing potential of AgInS2 nanoparticles for use as practical cadmium-free quantum dots.