Class Of Luminescent Materials Research Articles

A Rising Star: Luminescent Carbene-Metal-Amide Complexes.

Coinage metal (gold, silver, and copper) complexes are attractive candidates to substitute the widely studied noble metal complexes, such as, iridium(III) and platinum(II), as luminescent materials in organic light-emitting diodes (OLEDs). However, the development of coinage metal complexes exhibiting high emission quantum yields and short exciton lifetimes is still a formidable challenge. In the past few years, coinage metal complexes featuring a carbene-metal-amide (CMA) motif have emerged as a new class of luminescent materials in OLEDs. Thanks to the coinage metal-bridged linear geometry, coplanar conformation, and the formation of excited states with dominant ligand-to-ligand charge transfer character and reduced metal d-orbital participation, most CMA complexes have high radiative rates via thermally activated delayed fluorescence. Currently, the family of CMA complexes have rapidly evolved and remarkable progresses in CMA-based OLEDs have been made. Here, a Concept article on CMA complexes is presented, with a focus on molecular design principles, the correlation between molecular structure/conformation and optoelectronic properties, as well as OLED performance. The future prospects of CMA complexes are also discussed.

MICROWAVE-ASSISTED SYNTHESIS OF Cr-DOPED Gd2O3 NANOSTRUCTURES AND INVESTIGATION ON MORPHOLOGY, OPTICAL, AND PHOTOLUMINESCENCE PROPERTIES

In the present study, pure and chromium (Cr)-doped gadolinium oxide (Gd2O3) nanostructures (NSs) (2%, 5%, and 8%) were successfully synthesized by a microwave-assisted solution process technique. The X-ray diffraction and scanning electron microscopy results revealed that single-phase crystals appeared in up to 8% of the Cr-doped NSs and a secondary phase of GdCr2O4 formed beyond an 8% increase in Cr concentration. The spherical-shaped morphology observed for Cr:Gd2O3 NSs had average particle sizes varying between 80 and 150 nm. The ultraviolet-visible spectroscopic results exhibited absorption maxima between 345.1 and 411. 1 nm and the Eg value decreased from 3.46 to 2.85 eV as the Cr concentration increased. The X-ray photoelectron spectroscopy results suggested that the Cr+3 ions were well incorporated into the Gd2O3 NSs, with a high-energy Gd 3d3/2 peak appearing at 1222 eV. The room temperature photoluminescence spectra exhibited a blue emission peak, which was found to increase with an increase in the Cr content. In addition, a broad emission peak appeared at 463.4-495.5 nm, which is characteristic for Cr insertion in Gd2O3 NSs; an increase in Cr+3 ions beyond 8% supressed the blue emission peak. The results strongly suggest that the Cr:Gd2O3 NSs form a new class of luminescent materials.

Responsive Sensors of Upconversion Nanoparticles.

Upconversion nanoparticles are a class of luminescent materials that convert longer-wavelength near-infrared photons into visible and ultraviolet emissions. They can respond to various external stimuli, which underpins many opportunities for developing the next generation of sensing technologies. In this perspective, the unique stimuli-responsive properties of upconverting nanoparticles are introduced, and their recent implementations in sensing are summarized. Promising material development strategies for enhancing the key sensing merits, including intrinsic sensitivity, biocompatibility and modality, are identified and discussed. The outlooks on future technological developments, novel sensing concepts, and applications of nanoscale upconversion sensors are provided.

Synthesis and Luminescent Properties of Carbon Nanodots Dispersed in Nanostructured Silicas.

Luminescent carbon nanoparticles are a relatively new class of luminescent materials that have attracted the increasing interest of chemists, physicists, biologists and engineers. The present review has a particular focus on the synthesis and luminescent properties of carbon nanoparticles dispersed inside nanostructured silica of different natures: oxidized porous silicon, amorphous thin films, nanopowders, and nanoporous sol–gel-derived ceramics. The correlations of processing conditions with emission/excitation spectral properties, relaxation kinetics, and photoluminescence photodegradation behaviors are analyzed. Following the evolution of the photoluminescence (PL) through the “from-bottom-to-up” synthesis procedure, the transformation of molecular-like ultraviolet emission of organic precursor into visible emission of carbon nanoparticles is demonstrated. At the end of the review, a novel method for the synthesis of luminescent and transparent composites, in form of nanoporous silica filled with luminescent carbon nanodots, is presented. A prototype of white light emitting devices, constructed on the basis of such luminophores and violet light emitting diodes, is demonstrated.

Recent Advances in Aggregation-Induced Emission Materials and Their Biomedical and Healthcare Applications.

The emergence of the concept of aggregation-induced emission (AIE) has opened new opportunities in many research areas, such as biopsy analysis, biological processes monitoring, and elucidation of key physiological and pathological behaviors. As a new class of luminescent materials, AIE luminogens (AIEgens) possess many prominent advantages such as tunable molecular structures, high molar absorptivity, high brightness, large Stokes shift, excellent photostability, and good biocompatibility. The past two decades have witnessed a dramatic growth of research interest in AIE, and many AIE-based bioprobes with excellent performance have been widely explored in biomedical fields. This review summarizes some of the latest advancements of AIE molecular probes and AIE nanoparticles (NPs) with regards to biomedical and healthcare applications. According to the research areas, the review is divided into five sections, which are imaging and identification of cells and bacteria, photodynamic therapy, multimodal theranostics, deep tissue imaging, and fluorescence-guided surgery. The challenges and future opportunities of AIE materials in the advanced biomedical fields are briefly discussed. In perspective, the AIE-based bioprobes play vital roles in the exploration of advanced bioapplications for the ultimate goal of addressing more healthcare issues by integrating various cutting-edge modalities and techniques.

Afterglow Carbon Dots: From Fundamentals to Applications.

The ability of carbon dots (CDs) to emit afterglow emission in addition to fluorescence in response to UV-to-visible excitation allows them to be a new class of luminescent materials. When compared with traditional organic or inorganic afterglow materials, CDs have a set of advantages, including small size, ease of synthesis, and absence of highly toxic metal ions. In addition, high dependence of their afterglow color output on temperature, excitation wavelength, and aggregation degrees adds remarkable flexibility in the creation of multimode luminescence of CDs without the need for changing their intrinsic attributes. These characteristics make CDs particularly attractive in the fields of sensing, anticounterfeiting, and data encryption. In this review, we first describe the general attributes of afterglow CDs and their fundamental afterglow mechanism. We then highlight recent strategic advances in the generation or activation of the afterglow luminescence of CDs. Considerable emphasis is placed on the summarization of their emergent afterglow properties in response to external stimulation. We further highlight the emerging applications of afterglow CDs on the basis of their unique optical features and present the key challenges needed to be addressed before the realization of their full practical utility.

Tunable upconversion of holmium sublattice through interfacial energy transfer for anti-counterfeiting.

Photon upconversion is a fascinating phenomenon that can convert low-energy photons to high-energy photons efficiently. However, most previous relevant research has been focused on upconversion systems with a sufficiently low lanthanide emitter concentration, such as 2 mol% for Er3+ in an Er-Yb coupled system. Realizing the upconversion from lanthanide heavily doped systems in particular, the emitter sublattice is still a challenge. Here, we report a mechanistic strategy to achieve the intense upconversion of the holmium sublattice in a core-shell-based nanostructure design through interfacial energy transfer channels. This design allowed a spatial separation of Ho3+ and sensitizers (e.g., Yb3+) into different regions and unwanted back energy transfers between them could then be minimized. By taking advantage of the dual roles of Yb3+ as both a migrator and energy trapper, a gradual color change from red to yellowish green was achievable upon 808 nm excitation, which could be further markedly enhanced by surface attaching indocyanine green dyes to facilitate the harvesting of the incident excitation energy. Moreover, emission colors could be tuned by applying non-steady state excitation. Such a fine-tunable color behavior holds great promise in anti-counterfeiting. Our results present a facile but effective conceptual model for the upconversion of the holmuim sublattice, which is helpful for the development of a new class of luminescent materials toward frontier applications.

Origin of the Photoluminescence of Metal Nanoclusters: From Metal-Centered Emission to Ligand-Centered Emission.

Recently, metal nanoclusters (MNCs) emerged as a new class of luminescent materials and have attracted tremendous interest in the area of luminescence-related applications due to their excellent luminous properties (good photostability, large Stokes shift) and inherent good biocompatibility. However, the origin of photoluminescence (PL) of MNCs is still not fully understood, which has limited their practical application. In this mini-review, focusing on the origin of the photoemission emission of MNCs, we simply review the evolution of luminescent mechanism models of MNCs, from the pure metal-centered quantum confinement mechanics to ligand-centered p band intermediate state (PBIS) model via a transitional ligand-to-metal charge transfer (LMCT or LMMCT) mechanism as a compromise model.

Control synthesis, subtle surface modification of rare-earth-doped upconversion nanoparticles and their applications in cancer diagnosis and treatment.

Rare earth doped upconversion nanoparticles (UCNPs) are a new class of luminescent materials that can absorb long-wavelength near-infrared photons and emit short-wavelength UV-visible photons. UCNPs have little damage to biological tissues, have deep tissue penetration ability, have no background fluorescence noise interference, have high imaging sensitivity, and have no photobleaching effect. In the field of biomedicine, especially in the field of diagnosis and treatment of cancer, a wide range of research interests has arisen. In this paper, we briefly introduce the luminescent principle of rare-earth doped UCNPs, discuss several widely used control synthesis and modification methods, and focus on the research progress of UCNPs in detection of cancer cells, photodynamic therapy (PDT) and photothermal therapy (PTT) field. We also summarize the application of UCNPs as a diagnostic and therapeutic integrated nanoplatform in the diagnosis and treatment of cancer. At last, we explore the application challenge and prospect of UCNPs in oncology field.

Preparation, characterization and cell cytotoxicity of Pd-doped CdTe quantum dots and its application as a sensitive fluorescent nanoprobe

Dopants strongly affect properties and optical behaviors of quantum dots, therefore doped-QDs considered as a novel class of luminescent materials. Following development doping approach and using Pd2+ ions as a dopant, for the first time, in this study, a facile preparation of Pd-doped CdTe QDs was reported with thioglycolic acid as a stabilizer. The essential parameters of the synthesis conditions such as dopant concentration, reaction time and optical properties of the Pd: CdTe QDs was studied. The Pd: CdTe QDs with excellent photostability and biocompatibility, exhibited a greenish emission at 529 nm. Interestingly, these nanoparticles display high fluorescence sensitivity to diazinon (DZN). Under optimal conditions, a proposed sensor was designed based on Pd: CdTe QDs which represented a wide range of linear response (2.3–100 µM), low detection limit [3.3 nM, (S/N = 3)], high stability, and selectivity. Additionally, the newly sensing nanoprobe was used for the determination of DZN in environmental water samples with satisfactory results.

Surface Dynamics and Ligand-Core Interactions of Quantum Sized Photoluminescent Gold Nanoclusters.

Quantum-sized metallic clusters protected by biological ligands represent a new class of luminescent materials; yet the understanding of structural information and photoluminescence origin of these ultrasmall clusters remains a challenge. Herein we systematically study the surface ligand dynamics and ligand-metal core interactions of peptide-protected gold nanoclusters (AuNCs) with combined experimental characterizations and theoretical molecular simulations. We show that the peptide sequence plays an important role in determining the surface peptide structuring, interfacial water dynamics and ligand-Au core interaction, which can be tailored by controlling peptide acetylation, constituent amino acid electron donating/withdrawing capacity, aromaticity/hydrophobicity and by adjusting environmental pH. Specifically, emission enhancement is achieved through increasing the electron density of surface ligands in proximity to the Au core, discouraging photoinduced quenching, and by reducing the amount of surface-bound water molecules. These findings provide key design principles for understanding the surface dynamics of peptide-protected nanoparticles and maximizing the photoluminescence of metallic clusters through the exploitation of biologically relevant ligand properties.

Engineering the color output in a single upconversion microtube via intervention of the electronic population

The engineering of upconversion (UC) light color output is of great importance due to its promising application in biological imaging, data storage and solar cells. In this work, we showed that a tunable red-to-green emission ratio can be achieved by rationally designing the depopulation mechanism of intermediate state via increasing pump power density, pulse duration, pulse interval and Yb3+ concentration accompanied with the waveguide effect in a single Yb3+/Er3+ codoped NaYF4 microtube. We revealed that the red UC luminescence can be enhanced by three-photon process. As expected, three-photon and two-photon processes could be effectively switched by controlling pulse duration and power density. Compared with varying the power density, elevating the Yb concentration accompanied with the waveguide effect is more effective in modifying the color output. Our results provide insight into underlying physical mechanisms of intervening electronic population and present a general approach to constructing a new class of luminescent materials with tunable UC emissions.

High‐Speed OLEDs and Area‐Emitting Light‐Emitting Transistors from a Tetracyclic Lactim Semiconducting Polymer

AbstractDevelopment of a new class of luminescent materials that show high‐speed response, high charge carrier mobility, and high brightness is desirable toward realization of next generation of devices, such as electrically pumped organic lasers, visible light communication instruments, and organic light‐emitting transistors. In this paper, high‐speed organic light‐emitting diodes (OLEDs) and high‐performance hybrid light‐emitting transistors from a new type of solution processable luminescent material, poly[thiophene‐2,5‐diyl‐alt‐5,10‐bis((2‐hexyldecyl)oxy)dithieno[3,2‐c:3′,2′‐h][1,5]naphthyridine‐2,7‐diyl] (PTNT), are reported. The OLEDs based on PTNT polymer exhibit a peak brightness of 8 × 105 cd m−2 and 40 MHz modulation frequency under 10 ns pulse operation. This modulation frequency is significantly higher than that of commercially available LEDs, used for visible light communication. Additionally, solution‐processed area‐emitting hybrid light‐emitting transistors with an external quantum yield of 0.25% at brightness of 250 cd m−2 are demonstrated. Finally, the paper provides device physics and optoelectronic properties of PTNT polymer using ultraviolet photon spectroscopy, inversed photoelectron spectroscopy, and photophysical measurements.

Sequential Growth of Uniform β-NaYF₄@β-NaLnF₄ (Ln = Y, Lu, Yb) Microcrystals with Luminescent Properties of Multicolor Tuning and Dual-Mode Emission.

We synthesized the uniform core-shell microstructured compounds with hexagonal phase NaYF4:Er/Yb microrods as the core and hexagonal phase NaLnF4 (NaYbF4, NaLuF4:Yb/Tm, NaYF4:Yb/Er, NaYF4:Eu) as the shell based on the hydrothermal reaction. These microscale core-shell structures provided a platform for the spatially confining optical process while possessing high luminescence efficiency. The thickness of the shell could be controlled by adjusting the amounts of shell precursor, which significantly affected the intensity of the shell dopant ions emission and the emission color of core-shell upconversion luminescence (UCL). The uniform NaYF4@NaLnF4 (Ln = Y, Lu, Yb) microrods, with a series of rare-earth ions doped into the core and shell layer at various doping concentrations, achieved color-tuning of the upconversion (UC) emission and dual-mode emission at the single-microcrystal level, thus allowing the efficient utilization of core-shell microcrystals in the photonics and security labeling. This study suggests a new class of luminescent materials in the microscopic field.

Enhanced scintillation of Ba3In(B3O6)3 based on nitrogen doping

Scintillating materials, as a class of luminescent materials, are highly demanded for practical use in the high-energy detection. However, the applications are often hampered by their low light yield (LY) or long decay time for many traditional scintillators. In this work, upon nitrogen anion doping, scintillation performance in layered borate Ba3In(B3O6)3 (BIB) has been excellently enhanced with high XEL intensity of ～3 times as large as that of commercial Bi4Ge3O12 (BGO) and ultra-fast fluorescent decay time of ～1.25ns. To shed light on origins of the intrinsic violet-blue emission, we measured the in-situ vacuum ultraviolet excited (VUV) emission spectra of N-BIB ceramic. Combined with experiments and first principles calculations, the band-gap reduction and donor-acceptor density increasing by nitrogen (N) doping is responsible for the enhancement of scintillation performance for N-doped Ba3In(B3O6)3. Moreover, nitrogen anion doping rather than conventional cation doping is found to be also applicable to other intrinsic luminescent materials for enhancing performance.

Expedient synthesis of a phenanthro-imidazo-pyridine fused heteropolynuclear framework via CDC coupling: a new class of luminophores.

We herein report the design and synthesis of a group of fused phenanthro-imidazo[1,2-a]pyridine derivatives as a new class of luminescent materials through a Pd(ii) catalyzed intramolecular CDC (cross dehydrogenative coupling) reaction. This method thus unlocked a convenient & expedient way for the synthesis of a new molecular framework containing π-extended fused heteropolycycles. The heteropolycycles showed very good fluorescence properties both in solid and solution phases which were further utilized in live cell imaging. These kinds of molecules have potential to be used as therapeutic probes and also their solid state luminescence properties can be further utilized for making optoelectronic devices.

Luminescent Porous Polymers Based on Aggregation-Induced Mechanism: Design, Synthesis and Functions.

Enormous research efforts are focusing on the design and synthesis of advanced luminescent systems, owing to their diverse capability in scientific studies and technological developments. In particular, fluorescence systems based on aggregation-induced emission (AIE) have emerged to show great potential for sensing, bio-imaging, and optoelectronic applications. Among them, integrating AIE mechanisms to design porous polymers is unique because it enables the combination of porosity and luminescence activity in one molecular skeleton for functional design. In recent years rapid progress in exploring AIE-based porous polymers has developed a new class of luminescent materials that exhibit broad structural diversity, outstanding properties and functions and promising applications. By classifying the structural nature of the skeleton, herein the design principle, synthetic development and structural features of different porous luminescent materials are elucidated, including crystalline covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and amorphous porous organic polymers (POPs). The functional exploration of these luminescent porous polymers are highlighted by emphasizing electronic interplay within the confined nanospace, fundamental issues to be addressed are disclosed, and future directions from chemistry, physics and materials science perspectives are proposed.

Time-resolved fluorescence and absence of Förster resonance energy transfer in ferroelectric liquid crystal-quantum dots composites

The present article deals with the interaction of octadecylamine (ODA) capped cadmium selenide quantum dots (CdSe QDs) and two ferroelectric liquid crystals (FLCs) having different values of spontaneous polarization (Ps). The pristine FLCs and FLC-QDs composites have been investigated by using steady-state and time-resolved fluorescence spectroscopic techniques. Stokes shift and the preferred alignment of FLC molecules in the presence of QDs are found to depend on the secondary order parameter of FLCs (i.e. Ps). The secondary fluorescence emissions have been strongly influenced by the concentration of QDs. The Förster resonance energy Transfer (FRET) was absent in both the composites. This article discloses the role of various factors, like relative orientation, dipolar interaction between donor and acceptor and the proximity of QDs (>10 nm), which might be responsible for the absence of FRET. FLC-QDs composites do not form a new class of luminescent material though the fluorescence properties of host FLCs are tailored in the presence of QDs by means of the change in molecular alignment. The change in lifetimes of FLC-QDs composites has not been observed.

Lanthanide Ion Doped Upconverting Nanoparticles: Synthesis, Structure and Properties

Lanthanide doped upconverting nanoparticles (UCNPs) have emerged as a new class of luminescent materials, with major discoveries and overall significant progress during the last decade. Unlike multiphoton absorption in organic dyes or semiconductor quantum dots, lanthanide doped UCNPs involve real intermediate quantum states and convert infrared (IR) into visible light via sequential electronic excitation. The relatively high efficiency of this process even at low radiation flux makes UCNPs particularly attractive for many current and emerging areas of technology. The aim of this article is to highlight several recent advances in this rapidly growing field, emphasizing the relationships between structure and properties of UCNPs. Additionally, various strategies developed for the synthesis of UCNPs with a focus on the various synthetic approaches that yield high-quality monodisperse samples with controlled size, shape and crystalline phase are reviewed. Emerging synthetic approaches towards designed structure to improve the optical and electronic properties of UCNPs are discussed. Finally, recent examples of applications of UCNPs in biomedical and optoelectronics research, giving our own perspectives on future directions and emerging possibilities of the field are described.

Doping Triple Lanthanum Ions in GdPO4Nanocrystals Through Multiple Synthesis Routes and Their Dual Mode Spectrum Conversion Behaviour

Doping multiple lanthanum ions in crystal of nanometer dimensions to achieve desired properties is an arduous task. This has been achieved in an important lanthanum phosphate (GdPO4) via three different synthesis routes including soft chemical processes such as room temperature co precipitation and pechini type sol-gel method and a facile solid state diffusion reaction. All the methods produce well crystalline nanoparticles with dimensions ranging from few nm to tens of nm but with different morphology. The three lanthanum ions Ho3+, Yb3+, Eu3+ introduce up and down conversion luminescence in GdPO4 nanocrystals making them simultaneously excitable by UV and IR light and emit in the visible. The concept of dual excitation nanophosphor is quite unique for applications such as security ink and solar spectrum conversion for efficient energy harvesting. Intense orange red emission from Eu3+ (D-5(0) - F-7(J) transitions) under broad UV excitation range (250 nm-400 nm) and predominant red emission from Ho3+ (640-654 nm, F-5(5)-I-5(8)) through two to three photon UC process under IR (980 nm) excitation in GdPO4:Ho3+, Yb3+, Eu3+ suggest a general approach to constructing a new class of luminescent materials with simultaneous up and down conversion emissions by controlled manipulation of energy transfer within a nanoscopic region.