White-Emitting Gold Nanocluster Assembly with Dynamic Color Tuning.

We report that constructed Au nanoclusters (NCs) can afford amazing white emission synergistically dictated by the Au(0)-dominated core-state fluorescence and Au(I)-governed surface-state phosphorescence, with record-high absolute quantum yields of 42.1% and 53.6% in the aqueous solution and powder state, respectively. Moreover, the dynamic color tuning is achieved in a wide warm-to-cold white-light range (with the correlated color temperature varied from 3426 to 24 973 K) by elaborately manipulating the ratio of Au(0) to Au(I) species and thus the electron transfer rate from staple motif to metal kernel. This study not only exemplifies the successful integration of multiple luminescent centers into metal NCs to accomplish efficient white-light emission but also inspires a feasible pathway toward customizing the optical properties of metal NCs by regulating electron transfer kinetics.

Modulation of Nucleation and Growth Kinetics of Perovskite Nanocrystals Enables Efficient and Spectrally Stable Pure-Red Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) based on CsPb(Br/I)3 nanocrystals (NCs) usually suffer from severe spectral instability under operating voltage due to the poor-quality PeNCs. Herein, zeolite was utilized to prepare high-quality CsPb(Br/I)3 NCs via promoting the homogeneous nucleation and growth and suppressing the Ostwald ripening of PeNCs. In addition, the decomposed zeolite interacted strongly with PeNCs through Pb-O bonds and hydrogen bonds, which inhibited the formation of defects and suppressed halide ion migration, leading to an improved photoluminescence quantum yield (PLQY) and enhanced stability of PeNCs. Moreover, the strong binding affinity of decomposed zeolite to PeNCs contributed to the formation of homogeneous perovskite films with high PLQY. As a result, pure-red PeLEDs with Commission International de I'Eclairage (CIE) coordinates of (0.705, 0.291) were fabricated, approaching the Rec. 2020 red primary color. The devices achieved a peak external quantum efficiency of 23.0% and outstanding spectral stability.

High-Performance Blue Perovskite Light-Emitting Diodes Enabled by Synergistic Effect of Additives.

While quasi-two-dimensional (quasi-2D) perovskites have good properties of cascade energy transfer, high exciton binding energy, and high quantum efficiency, which will benefit high-efficiency blue PeLEDs, inefficient domain distribution management and unbalanced carrier transport impede device performance improvement. Herein, (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and methyl 2-aminopyridine-4-carboxylate (MAC) were simultaneously introduced to a blue quasi-2D perovskite film. Relying on the synergistic effect of 2PACz and MAC, it not only modulates the phase distribution inhibiting the n = 2 phase but also greatly improves the electrical property of the quasi-2D perovskite film. As a result, the as-modified blue quasi-2D PeLED demonstrated an external quantum efficiency (EQE) of 17.08% and a luminance of 10142 cd m-2. This study exemplifies the synergistic effect among dual additives and offers a new effective additive strategy modulating phase distribution and building balanced carrier transport, which paves the way for the fabrication of highly efficient blue PeLEDs.

Multiple Phase Regulation Enables Efficient and Bright Quasi-2D Perovskite Light-Emitting Diodes.

Quasi-2D perovskites, multiquantum well materials with the energy cascade structure, exhibit impressive optoelectronic properties and a wide range of applications in various optoelectronic devices. However, the insufficient exciton energy transfer caused by the excess of small-n phases that induce nonradiative recombination and the spatially random phase distribution that impedes charge transport severely inhibit the device performance of light-emitting diodes (LEDs). Here, a faster energy transfer process and efficient carrier recombination are achieved by introducing the multifunctional additive 2-(methylsulfonyl)-4-(trifluoromethyl)benzoic acid (MTA) to manipulate the crystallization process of perovskites. The introduction of MTA not only constrains the PEA and restrains the formation of small-n phases to improve the energy transfer process but also optimizes the crystal orientation to promote charge transport. As a result, highly efficient pure green quasi-2D perovskite LEDs with a peak EQE of 25.9%, a peak current efficiency of 108.1 cd A-1, and a maximum luminance of 288798 cd m-2 are achieved.

Engineering of Hole Transporting Interface by Incorporating the Atomic-Precision Ag6 Nanoclusters for High-Efficiency Blue Perovskite Light-Emitting Diodes.

Properties of the underlying hole transport layer (HTL) play a crucial role in determining the optoelectronic performance of perovskite light-emitting devices (PeLEDs). However, endowing the current HTL system with a deep highest occupied molecular orbital (HOMO) level concurrent with high hole mobility is still a big challenge, in particular being an open constraint toward high-efficiency blue PeLEDs. In this regard, employing the poly(9-vinylcarbazole) as a model, we perform efficient incorporation of the atomic-precision metal nanoclusters (NCs), [Ag6PL6, PL = (S)-4-phenylthiazolidine-2-thione], to achieve significant tailoring in both HOMO energy level and hole mobility. As a result, the as-modified PeLEDs exhibit an external quantum efficiency (EQE) of 14.29% at 488 nm. The presented study exemplifies the success of metal NC involved HTL engineering and offers a simple yet effective additive strategy to settle the blue PeLED HTL dilemma, which paves the way for the fabrication of highly efficient blue PeLEDs.

Multi-Species Surface Reconstruction for High-Efficiency Perovskite Nanocrystal Light-Emitting Diodes.

Although colloidal perovskite nanocrystal (PNC) solution has exhibited near-unity photoluminescence quantum yield (PLQY), the luminance would be severely quenched when the PNC solution is assembled into thin films due to the agglomeration and fusion of NCs caused by the exfoliation of surface ligands and non-radiative Förster resonance energy transfer (FRET) from small to large particle sizes, which seriously affected the performances of light-emitting diodes (LEDs). Here, we used Guanidine thiocyanate (GASCN) and Sodium thiocyanate (NaSCN) to achieve effective CsPbI3 PNC surface reconstruction. Due to the strong coordination ability of these small molecules with the anions and cations on the surface of the PNCs, they can provide strong surface protection against PNC fusion during centrifugal purification process and repair the surface defects of PNCs, so that the original uniform size distribution of PNCs can be maintained and FRET between close-packed PNC films is effectively suppressed, which allows the emission characteristics of the films to be preserved. As a result, highly oriented, smooth and nearly defect-free high-quality PNC thin films are obtained, with PLQY as high as 95.1 %, far exceeding that of the original film, and corresponding LEDs exhibit a maximum external quantum efficiency of 24.5 %.

Magnetic Field-Assisted Interface Embedding Strategy to Construct 2D/3D Composite Structure for Stable Perovskite Solar Cells with Efficiency Over 24.

Perovskite solar cells (PSCs) based on 2D/3D composite structure have shown enormous potential to combine high efficiency of 3D perovskite with high stability of 2D perovskite. However, there are still substantial non-radiative losses produced from trap states at grain boundaries or on the surface of conventional 2D/3D composite structure perovskite film, which limits device performance and stability. In this work, a multifunctional magnetic field-assisted interfacial embedding strategy is developed to construct 2D/3D composite structure. The composite structure not only improves crystallinity and passivates defects of perovskite layer, but also can efficiently promote vertical hole transport and provide lateral barrier effect. Meanwhile, the composite structure also forms a good surface and internal encapsulation of 3D perovskite to inhibit water diffusion. As a result, the multifunctional effect effectively improves open-circuit voltage and fill factor, reaching maximum values of 1.246 V and 81.36%, respectively, and finally achieves power conversion efficiency (PCE) of 24.21%. The unencapsulated devices also demonstrate highly improved long-term stability and humidity stability. Furthermore, an augmented performance of 21.23% is achieved, which is the highest PCE of flexible device based on 2D/3D composite perovskite films coupled with the best mechanical stability due to the 2D/3D alternating structure.

Intelligent interior atmosphere lamp system based on quantum dot LEDs for safe driving assistance.

A driver safety assisting system is essential to reduce the probability of traffic accidents. But most of the existing driver safety assisting systems are simple reminders that cannot improve the driver's driving status. This paper proposes a driver safety assisting system to reduce the driver's fatigue degree by the light with different wavelengths that affect people's moods. The system consists of a camera, an image processing chip, an algorithm processing chip, and an adjustment module based on quantum dot LEDs (QLEDs). Through this intelligent atmosphere lamp system, the experimental results show that blue light reduced the driver's fatigue degree when just turned on; but as time went on, the driver's fatigue degree rebounded rapidly. Meanwhile, red light prolonged the driver's awake time. Different from blue light alone, this effect can remain stable for a long time. Based on these observations, an algorith was designed to quantify the degree of fatigue and detect its rising trend. In the early stage, the red light is used to prolong the awake time and the blue light to suppress when the fatigue value increases, so as to maximize the awake driving time. The result showed that our device prolonged the awake driving time of the drivers by 1.95 times and reduced fatigue during driving: the quantitative value of fatigue degree generally decreased by about 0.2 times. In most experiments, the subjects were able to complete four hours of safe driving, which reached the maximum length of continuous driving at night allowed by China laws. In conclusion, our system changes the assisting system from a reminder to a helper, thus effectively reducing the driving risk.

Wide-coverage and Efficient NIR Emission from Single-component Nanophosphors through Shaping Multiple Metal-halide Packages.

Wide-coverage near infrared (NIR) phosphor-converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide-coverage NIR phosphors. Here, we report the single-component lanthanide (Ln3+ ) ions doped Cs2 M(In0.95 Sb0.05 )Cl6 (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd-Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs2 M(In1-x Sbx )Cl6 NCs can break the forbidden of f-f transition of Ln3+ , thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln3+ . Finally, the wide-coverage NIR LEDs based on Sm3+ , Nd3+ , Er3+ -tridoped Cs2 K0.5 Rb0.5 (In0.95 Sb0.05 )Cl6 NCs are fabricated and employed in the multiplex gas sensing and night-vision application.

Synergistic Regulation Effect of Nitrate and Calcium Ions for Highly Luminescent and Robust α-CsPbI3 Perovskite.

The α-CsPbI3 nanocrystals (NCs) easily transform into yellow non-perovskite, accompanying with declining photoelectric properties that restricting their practical applications in diverse fields. Herein, the highly luminescent and robust α-CsPbI3 NCs is achieved through engineering the lattice symmetry of perovskite, enabled by the synergistic effect of NO3- ion passivation and Ca2+ ion doping. The introduced NO3- ions enhance the phase-change energy barrier and the surface steric hindrance, thus promoting the formation of α-CsPbI3 NCs with hyper-symmetric crystal structure, while the Ca2+ ion doping contributes to improving their lattice symmetry by significant regulation of the tolerance factor. As a result, the obtained α-CsPbI3 NCs display an outstanding photoluminescence quantum yield of 96.6%, together with the reduced defect state density and eminent conductivity. Most importantly, the as-engineered α-CsPbI3 NCs exhibit excellent stability under ambient conditions for 9 months and UV illumination for 32 h. It displays brilliant thermal stability, maintaining luminous intensity for 15 min under 140 °C, and performing desired durability and reversibility, evidenced by 160 °C cyclic test and 120 °C reversibility test. Given enhanced robustness, the as-engineered α-CsPbI3 NCs based light-emitting-diode devices are constructed, exhibiting a power efficiency of 105.3 lm W-1 and the excellent working stability for 18 h.

How does social support affect public service motivation of healthcare workers in China: the mediating effect of job stress.

BACKGROUND: This study aimed to examine relations between social support, job stress, and public service motivation (PSM), also assessed how social support and job stress affect PSM in China based on the job demands-resources (JD-R) theory. METHODS: The survey investigated a sample of 973 healthcare workers employed in public hospitals in Beijing, Xiamen, and Guangzhou in 2017 (including doctors, nurses, medical technicians, and administrators). Correlation analysis and Structural equation modeling (SEM) were used. RESULTS: Challenge stress and hindrance stress were directly negatively associated with PSM. Supervisor support was significantly positively associated with PSM, and the path from coworker support to PSM was significant. Supervisor support was significantly negatively associated with hindrance stress, and coworker support was significantly negatively associated with challenge stress. Hindrance stress and challenge stress significantly mediated the relations between supervisor support and PSM, and between coworker support and PSM respectively. PSM might be raised by increasing supervisor support and coworker support and by limiting hindrance stress and challenge stress. CONCLUSION: Our study suggests that administrators of public hospitals should be mindful of the intense job stress of healthcare workers and undertake interventions targeting challenge stress and hindrance stress. Also, public hospital administrators should encourage and assist supervisors in their leadership functions. Besides, administrators of public hospitals should emphasize coworker support and good employee relationships.

Self-Assembly of Au Nanoclusters into Helical Ribbons by Manipulating the Flexibility of Capping Ligands.

Self-assembly is a powerful technology to construct nanomaterials with helical structures. However, using metal nanoclusters (NCs) as the building blocks for the construction of helical architectures is still rarely reported. In this paper, Au NC assembled helical ribbons (Au NCHRs) are successfully constructed by using Au NCs as the building blocks. Effects of heating mode, solvent polarity and ligand length on the self-assembly process of Au NCs are discussed. The results indicate that the lengths of overlapped and nonoverlapped ligands between adjacent Au NCs play the dominated role on adjusting the morphologies of the resulting assemblies. Ligands with appropriate overlap can provide sufficient flexibility for the helical assembly of Au NCs without losing the stability. If the length of the overlapped parts is too long, the assemblies are usually rigid without the helical structure. Instead, the overlength of nonoverlapped ligands will boost the flexibility but damage the structural stability of the assemblies. Since everything in the world is assembled by atoms and molecules, recognizing the self-assembly mechanism of NCs may promote our understanding on the bountiful complexity of life and nature.

Unraveling the Impact of Gold(I)-Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters.

Aggregation-induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. This communication reveals the impact of surface AuI -thiolate motifs on the AIE properties of Au NCs, by employing a series of water-soluble glutathione (GSH)-coordinated Au complexes and NCs as a model ([Au10 SR10 ], [Au15 SR13 ], [Au18 SR14 ], and [Au25 SR18 ]- , SR=thiolate ligand). Spectroscopic investigations show that the emission wavelength of Au NCs is adjustable from visible to the near-infrared II (NIR-II) region by controlling the length of the AuI -SR motifs on the NC surface. Decreasing the length of AuI -SR motifs also changes the origin of cluster luminescence from AIE-type phosphorescence to Au0 -core-dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in solution.

Aurophilic Interactions in the Self-Assembly of Gold Nanoclusters into Nanoribbons with Enhanced Luminescence.

Aurophilic interactions (AuI ⋅⋅⋅AuI ) are crucial in directing the supramolecular self-assembly of many gold(I) compounds; however, this intriguing chemistry has been rarely explored for the self-assembly of nanoscale building blocks. Herein, we report on studies on aurophilic interactions in the structure-directed self-assembly of ultrasmall gold nanoparticles or nanoclusters (NCs, <2 nm) using [Au25 (SR)18 ]- (SR=thiolate ligand) as a model cluster. The self-assembly of NCs is initiated by surface-motif reconstruction of [Au25 (SR)18 ]- from short SR-[AuI -SR]2 units to long SR-[AuI -SR]x (x>2) staples accompanied by structure modification of the intrinsic Au13 kernel. Such motif reconstruction increases the content of AuI species in the protecting shell of Au NCs, providing the structural basis for directed aurophilic interactions, which promote the self-assembly of Au NCs into well-defined nanoribbons in solution. More interestingly, the compact structure and effective aurophilic interactions in the nanoribbons significantly enhance the luminescence intensity of Au NCs with an absolute quantum yield of 6.2 % at room temperature.

Contribution of Metal Defects in the Assembly Induced Emission of Cu Nanoclusters.

Aggregation/assembly induced emission (AIE) has been observed for metal nanoclusters (NCs), but the origin of the enhanced emission is not fully understood, yet. In this work, the significant contribution of metal defects on AIE is revealed by engineering the self-assembly process of Cu NCs using ethanol. The presence of ethanol leads to a rapid assembly of NCs into ultrathin nanosheets, promoting the formation of metal defects-rich surface. Detailed studies and computer simulation confirm that the metal defects-rich nanosheets possess increased Cu(I)-to-Cu(0) ratio, which greatly influences ligand-to-metal-metal charge transfer and therewith facilitates the radiative relaxation of excitons. Consequently, the Cu NCs self-assembly nanosheets exhibit obvious emission enhancement.

Near-Infrared Light-Stimulus-Responsive Film as a Sacrificial Layer for the Preparation of Free-Standing Films.

It remains a challenge to fabricate sacrificial films that are stable in most of solvents and can be readily decomposed on demand. Here we report the fabrication of a near-infrared (NIR) light decomposable sacrificial film by layer-by-layer (LbL) assembly of UV-light-decomposable poly((4-(2-bromoethoxy)-5-methoxy-2-nitrobenzyl acrylate) triethylammonium bromide) (PNBA-TEA), poly(sodium 4-styrene-sulfonate) (PSS), branched polyethyleimine (bPEI), and lanthanide-doped upconversion nanoparticles (UCNPs). The [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films are stable in deposition solutions of various materials and decompose upon NIR light irradiation. In the [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films, UCNPs can convert NIR light into UV light, which can decompose PNBA-TEA. After immersing the NIR light-irradiated [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films in 0.1 M aqueous NaHCO3 solution, the disintegration of the entire films occurs because of the repulsive force between the negatively charged photoproduct of PNBA-TEA and PSS. LbL-assembled (PAH/PAA)*50 films deposited on top of the NIR-light-decomposable [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films can be conveniently released to produce large-area and defect-free (PAH/PAA)*50 free-standing films after NIR light irradiation and subsequent immersion in 0.1 M aqueous NaHCO3 solution. Because of the satisfactory stability and on-demand decomposable property, the [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films are promising as sacrificial layers for the fabrication of various free-standing films.

Assembly-Induced Enhancement of Cu Nanoclusters Luminescence with Mechanochromic Property.

Metal nanoclusters (NCs) as a new class of phosphors have attracted a great deal of interest owing to their unique electronic structure and subsequently molecule-like optical properties. However, limited successes have been achieved in producing the NCs with excellent luminescent performance. In this paper, we demonstrate the significant luminescence intensity enhancement of 1-dodecanethiol (DT)-capped Cu NCs via self-assembly strategy. By forming compact and ordered assemblies, the original nonluminescent Cu NCs exhibit strong emission. The flexibility of self-assembly allows to further control the polymorphism of Cu NCs assemblies, and hence the emission properties. Comparative structural and optical analysis of the polymorphic NCs assemblies permits to establish a relationship between the compactness of assemblies and the emission. First, high compactness reinforces the cuprophilic Cu(I)···Cu(I) interaction of inter- and intra-NCs, and meanwhile, suppresses intramolecular vibration and rotation of the capping ligand of DT, thus enhancing the emission intensity of Cu NCs. Second, as to the emission energy that depends on the distance of Cu(I)···Cu(I), the improved compactness increases average Cu(I)···Cu(I) distance by inducing additional inter-NCs cuprophilic interaction, and therewith leads to the blue shift of NCs emission. Attributing to the assembly mediated structural polymorphism, the NCs assemblies exhibit distinct mechanochromic and thermochromic luminescent properties. Metal NCs-based white light-emitting diodes are further fabricated by employing the NCs assemblies with blue-green, yellow, and red emissions as phosphors.

Colloidal self-assembly of catalytic copper nanoclusters into ultrathin ribbons.

Metal nanoclusters (NCs) with diameter below 2 nm are promising catalysts in oxygen reduction reactions (ORR). However, the high surface energy of ultra-small clusters leads to structural instability, shedding doubt on practical applications. Herein, we demonstrate a self-assembly method to improve the durability of catalytic metal NCs, employing copper NCs capped by 1-dodecanethiol (DT) to form free-standing ribbons in colloidal solution. By tuning the cooperation between the dipolar attraction between Cu NCs and the van der Waals attraction between DT, the thickness of ribbons is adjusted to a single NC scale. Such free-standing ribbons exhibit excellent catalytic activity and durability in ORR.

Multiscale Bioresponses of Metal Nanoclusters.

Metal nanoclusters (NCs) are well-recognized novel nano-agents that hold great promise for applications in nanomedicine because of their ultrafine size, low toxicity, and high renal clearance. As foreign substances, however, an in-depth understanding of the bioresponses to metal NCs is necessary but is still far from being realized. Herein, this review is deployed to summarize the biofates of metal NCs at various biological levels, emphasizing their multiscale bioresponses at the molecular, cellular, and organismal levels. In the parts-to-whole schema, the interactions between biomolecules and metal NCs are discussed, presenting typical protein-dictated nano-bio interfaces, hierarchical structures, and in vivo trajectories. Then, the accumulation, internalization, and metabolic evolution of metal NCs in the cellular environment and as-imparted theranostic functionalization are demonstrated. The organismal metabolism and transportation processes of the metal NCs are subsequently distilled. Finally, this review ends with the conclusions and perspectives on the outstanding issues of metal NC-mediated bioresponses in the near future. This review is expected to provide inspiration for tailoring the customization of metal NC-based nano-agents to meet practical requirements in different sectors of nanomedicine.

Self-assembly of Au15 into single-cluster-thick sheets at the interface of two miscible high-boiling solvents.

Wet (nano)blanket: The self-assembly of Au nanoclusters into single-cluster-thick nanosheets is performed in two miscible high-boiling solvents with a slight polarity difference, which generates microphase separation and acts as a soft template to direct the self-assembly in a two-dimensional orientation.