Optimal Quantum Yield Research Articles

In situ preparation of two-dimensional ytterbium ions doped all-inorganic perovskite nanosheets for high-performance visual dual-bands photodetectors

Two-dimensional (2D) all-inorganic halide perovskites exhibit impressive optical and electrical properties, which are attracting extensive current interests. Rare earth (RE) ions doping is a significant method to adjust their optical, electrical properties and realize various applications. However, 2D RE ions-doped perovskite crystals have been rarely reported. Herein, we reported the synthesis of novel 2D all-inorganic perovskite CsPbClxBr3−x nanosheets (NSs) doped with RE ions. The octylamine (OLAm) with short carbon chains is used to tune the growth orientation for the preparation of 2D perovskite NSs. The morphology of the NSs can be adjusted by varying the ratio of shorter ligands to longer ligands and changing the temperature. The Yb3+ ions doped CsPbClBr2 NSs demonstrate an excitonic emission of perovskite host and a quantum cutting emission of Yb3+ ions at 985 nm with the optimal photoluminescence quantum yield (PLQY) of 128%. The results of femtosecond time-resolved transient absorption spectroscopy and DFT calculations indicate that the defect density of NSs is largely decreased and the photostability is enhanced induced by the passivation effect of Yb3+ ions. The photodetector (PD) based on lateral assembled Yb3+ ions doped CsPbClBr2 NS film is fabricated, which demonstrates a high responsivity and dual-band detection capability. The as-fabricated PDs are sensitive to both UV and NIR light, showing the responsivity of 1.96 A W−1, 0.12 mA W−1, the detectivity of 5 × 1012, 2.15 × 109 Jones at 440 nm and 980 nm, respectively. Finally, based on an imaging system with a PD array and a data analysis system, visual photoelectric detection is realized, and high-contrast images of the measured UV and NIR light are displayed. This work paves the way to tune the properties of 2D perovskite materials and develop high-performance optoelectronic devices.

Dynamics of Fucus serratus thallus photosynthesis and community primary production during emersion across seasons: canopy dampening and biochemical acclimation

The brown alga Fucus serratus forms dense stands on the sheltered low intertidal rocky shores of the Northeast Atlantic coast. In the southern English Channel, these stands have proved to be highly productive, particularly during emersion periods. Here, we studied the dampening effect of the canopy cover, associated with physiological and biochemical acclimation processes, that allows this species to withstand emersion stress. The F. serratus community primary production and the photosynthetic performance of thalli were concurrently followed in situ, throughout the midday emersion period, in different seasons and under various weather conditions. In addition, thallus samples were taken at various tidal stages to determine their content in biochemical compounds involved in photoprotective and antioxidant mechanisms. Under high light and temperature, the F. serratus community exhibited high aerial production rates (sometimes exceeding 1 g C m-2 h-1) that never decreased to less than 59% of the initial value during the emersion period. Under mild weather conditions, photosynthesis in thalli at the top of the canopy (measured as the relative electron transport rate) varied in response to changing incident light. Under harsh weather conditions (i.e. high light and temperature), the effective quantum yield of photosystem II (ΦPSII) dramatically decreased in thalli at the top of the canopy, but remained high in thalli at the bottom of or within the canopy. Due to self-shading, photosynthesis was light-limited in thalli in the lowest layer of the canopy, but was effective in thalli in the intermediate layers. Photoinhibition was observed in thalli at the top of the canopy (as a dramatic decrease in the optimal photosynthetic quantum yield Fv/Fm), but not in thalli beneath the canopy. At the end of the emersion period, Fv/Fm was strongly correlated to the relative water content of thalli. The findings from our simultaneous analysis of biochemical and photosynthetic parameters suggest coordination between the xanthophyll and the ascorbateglutathione cycles that varies with season. An accumulation of hydrogen peroxide was nevertheless observed once, indicating that oxidative stress is nonetheless possible under particularly harsh conditions.

Green Synthesis of Tunable Fluorescent Carbon Quantum Dots from Lignin and Their Application in Anti-Counterfeit Printing.

Lignin converted to carbon quantum dots (CQDs) attracts tremendous attention for large-scale production of carbon nanomaterials and value-added disposal of biomass wastes (such as the black liquor from pulping industry and the residue from hydrolysis of biomass). The green synthesis of lignin-derived CQDs is reported via a facile two-step method with the adjustment of acid additives containing N or S. The resulting series of CQDs exhibit bright fluorescence in gradient colors from blue to yellowish green, among which the N, S co-doped CQDs with the addition of 2,4-diaminobenzene sulfonic acid show an optimal fluorescence quantum yield (QY) of 30.5%. The red-shift photoluminescence emission behaviors of these CQDs can be attributed to the increased graphitization degree and reduced optical energy band gaps (2.47 → 2.17 eV) with regard to the incorporation of various heteroatoms. The improved fluorescence QYs are consistent with the variation trend of the increased N/C content in the CQDs. The yellowish green-emissive CQDs with bright fluorescence, strong water solubility, and excellent chemical stability perform well in anti-counterfeiting printing. The promising and sustainable approach for the synthesis of tunable fluorescent CQDs exhibits the value-added utilization of lignin for the fluorescence ink production.

Efficient dual-mode emissions of high-concentration erbium ions doped lead-free halide double perovskite single crystals

Lead-free halide double perovskites have attracted great attention due to the intriguing optoelectronic properties. However, the related researches mainly focus on their down-shifting (DS) luminescence process，while the up-conversion (UC) luminescence process is still rarely studied. Herein, Er3+ ions doped Cs2Ag0.6Na0.4InCl6:0.3%Bi double perovskite single crystals were prepared by an improved hydrothermal method, and the efficient UC and DS emission of Er3+ ions were realized by high-level doping concentration of Er3+ ions. Interesting, the UC green emission of Er3+ ions can be all obtained under 808，980 and 1540 nm excitation, and the optimal photoluminescence quantum yield (PLQY) is 0.17%. To be emphasized, it is the UC luminescence of rare earth ions doped semiconductor materials, which is more advantages in the application of optoelectronic devices than the UC luminescence of rare earth ions doped insulator materials (e.g, NaYF4). Moreover, with the increase of Er3+ ions doping concentration, the DS luminescence color can be controlled from yellow to green. And the near-infrared (NIR) light with the peak at 1540 nm is simultaneously emitted, and the highest PLQY reaches 38.36%, which is suitable for optical communication. Notably, the NIR light (1540 nm) can be also obtained under 808 and 980 nm excitation, which has positive significance for biological applications. This work demonstrates that rare earth ions doping has the potential to impart new functions to double perovskites.

Summer Heatwave Impacts on the European Kelp Saccharina latissima Across Its Latitudinal Distribution Gradient

Kelps are important foundation species in coastal ecosystems currently experiencing pronounced shifts in their distribution patterns caused by ocean warming. While some populations found at species’ warm distribution edges have been recently observed to decline, expansions of some species have been recorded at their cold distribution edges. Reduced population resilience can contribute to kelp habitat loss, hence, understanding intraspecific variations in physiological responses across a species’ latitudinal distribution is crucial for its conservation. To investigate potential local responses of the broadly distributed kelp Saccharina latissima to marine heatwaves in summer, we collected sporophytes from five locations in Europe (Spitsbergen, Bodø, Bergen, Helgoland, Locmariaquer), including populations exposed to the coldest and warmest local temperature regimes. Meristematic tissue from sporophytes was subjected to increasing temperatures of Δ+2, Δ+4 and Δ+6°C above the respective mean summer temperatures (control, Δ±0°C) characteristic for each site. Survival and corresponding physiological and biochemical traits were analyzed. Vitality (optimum quantum yield, Fv/Fm) and growth were monitored over time and biochemical responses were measured at the end of the experiment. Growth was highest in northern and lowest in southern populations. Overall, northern populations from Spitsbergen, Bodø and Bergen were largely unaffected by increasing summer temperatures up to Δ+6°C. Conversely, sporophytes from Helgoland and Locmariaquer were markedly stressed at Δ+6°C: occurrence of tissue necrosis, reduced Fv/Fm, and a significantly elevated de-epoxidation state of the xanthophyll cycle (DPS). The variations in phlorotannins, mannitol and tissue C and N contents were independent of temperature treatments and latitudinal distribution pattern. Pronounced site-specific variability in response to increasing temperatures implies that exceeding a threshold above the mean summer temperature exclusively affect rear-edge (southernmost) populations.

Physiological Characterization of Young 'Hass' Avocado Plant Leaves Following Exposure to High Temperatures and Low Light Intensity.

The worldwide demand for avocados has resulted in the planting of millions of young plants each year. However, global warming, resulting in high temperatures, sensed as heat stress, may severely damage these new plantings. The objective of this study was to assess the risks of heat stress on young avocado plants. We aimed to characterize different physiological parameters of young ‘Hass’ plant leaves following exposure to high temperatures under low light (LL) intensity and to pinpoint the temperature threshold for significant heat stress damage in these plants. To this end, young potted plants were subjected to different temperature gradients in a controlled-climate chamber. Minor and severe leaf damage was apparent in plants subjected to the 51 °C and 53 °C treatments, respectively. Minor and vast reductions in optimal quantum yield efficiency of photosystem II (Fv/Fm) values were observed in plants subjected to 51 °C and 53 °C, respectively. Heat stress treatments significantly reduced CO2 assimilation in plants subjected to 49 °C and higher temperatures. Stomatal conductance to water vapour and substomatal internal CO2 concentration were less sensitive to the heat treatments. These results imply that the heat damage threshold for young avocado plants under LL conditions is between 49 °C and 51 °C, whereas at 53 °C, severe and irreversible leaf damage occurs.

High light-induced photoinhibition is not limiting seedling establishment at abrupt treeline ecotones in New Zealand.

Seedlings of New Zealand's treeline-forming Fuscospora cliffortioides (Hook.f.) perform poorly beyond the established canopy, limiting treeline advance. To test the long-standing assumption that photoinhibition impairs regeneration in the subalpine belt of New Zealand's Southern Alps, we assessed photosystem II (PSII) performance of seedling-sized individuals and microclimate variation. We performed diurnal, non-invasive chlorophyll-a-fluorescence measurements on exposed and canopy-sheltered individuals at two sites in New Zealand's Southern Alps during summer and winter. Diurnal recordings of the effective (ΦPSII) and optimal (Fv/Fm) photosynthetic quantum yield were supplemented with light response curves and micro-temperature recordings. ΦPSII returned to near-optimal values around 0.8 after 30min of shading, which rules out accumulative or long-term photoinhibition effects. The maximum electron transport rate derived from rapid light curves was significantly higher (+12%) in exposed compared with canopy-shaded individuals. Summer temperature fluctuated widely on the scree (-0.5 to 60.5°C) and near seedlings (-2 to 26.5°C). Our results revealed a remarkable level of light adaptation and contradict previous studies hinting at high light-induced photoinhibition as a treeline-limiting factor in the Southern Alps. By linking low ΦPSII on winter mornings, and large, sudden temperature drops in summer, we suspect that cold-induced photoinhibition might occur but the rapid recovery of ΦPSII seen across a wide temperature range makes lethal photo-oxidative damage rather unlikely. Given the demonstrably low summer frost tolerance of F. cliffortioides, cold-related damage resulting from frost events during the growing season or embolism induced by frost drought may offer more plausible explanations for the poor seedling establishment. Duration and frequency of these events could diminish with global warming, which may promote treeline advance.

A precisely space-separated strategy of donor-acceptor for intense red emitting composite borosilicate glass co-doped with CsPbCl3 quantum dots and Mn2+ ions

Optical ions doped transparent glasses have attracted more and more attention because of their potential application in photonic applications. Unfortunately, optically active dopants occupy at non-crystalline coordination environment, which leads to their poor luminescence efficiency. Therefore, how to enhance luminescence efficiency of optically active dopants in glasses remains a great challenge. Here, we proposed a precisely space-separated strategy of donor-acceptor and successfully developed an intense red emitting composite borosilicate glass co-doped with CsPbCl3 quantum dots and Mn2+ ions. By rationally controlling post heat-treatment, CsPbCl3 QDs acting as donor were uniformly precipitated in glass and Mn2+ ions acting as acceptor are close to CsPbCl3 QDs but not inside CsPbCl3 QDs. Benefitted from high absorption efficiency of CsPbCl3 QDs and efficient energy transfer from CsPbCl3 QDs to Mn2+ ions in glasses, Mn2+ ions give an intense red broadband emission at 650 nm, 11 times as intense as the one without CsPbCl3 QDs. The optimal external quantum yield of the as-synthesized composite borosilicate glass is estimated to be 28.5%, 9.5 times as large as 3% for the one without CsPbCl3 QDs. The precise space-separation and energy transfer rate dependent non-radiative energy coupling mechanism was reasonably proposed to explain how CsPbCl3 QDs highly absorb energy, efficiently transfer it and finally feeding Mn2+ ion. These results demonstrate that the strategy of using microcrystalline with high absorption efficiency as donor, for instance, CsPbX3 QDs, to pump optical activator ions as acceptor, for instance, Mn2+ ion in glass may be very promising for developing high luminescent performance ions-doped transparent glasses.

Excitation-energy transfer under strong laser drive

Strong molecule-light interaction enables the control of molecular structures and dynamical processes. A model with strong laser drive is proposed to greatly enhance the intermolecular distance of resonant energy transfer, where the molecules are strongly driven by an optical cavity. The optimal Rabi frequency and quantum yield of energy transfer are observed, resulting from the trade off between dipole-dipole interaction and molecule-cavity coupling. When the strong drive at certain Rabi frequency is applied, a larger spatial range of effective energy transfer and a slower decay rate with the distance compared to the F\"orster mechanism of resonant energy transfer are observed in our model. Our work sheds light on spectroscopic study of the cooperative energy transfer in molecular polaritons.

Directional charge transportation and Rayleigh scattering for the optimal in-band quantum yield of a composite semiconductor nano-photocatalyst

The work propose a novel technique based on wavelength dispersive in situ photoluminescence spectroscopy for diagnosing the wavelength dependent directional charge transportation and Rayleigh scattering enhanced in-band quantum yield.

Bright red YCl3-promoted CsPbI3 perovskite nanorods towards efficient light-emitting diode

Abstract One-dimensional (1D) CsPbI3 nanorods (NRs) possess the suitable bandgap, extinction coefficient, long exciton diffusion radius and directed conductive channel, which make them advantageous for numerous optoelectronic devices. However, the direct synthesis of high-quality CsPbI3 NRs remains a challenge. Here, we develop a direct and facile synthetic approach to prepare the CsPbI3 NRs by YCl3 promotion. The YCl3 is not only the inducement of anisotropic growth of NCs, but also the source of passivator for improving the stability of NCs. Because of an effective YCl3 passivation, the efficient red emitting CsPbI3 NCs with photoluminescence quantum yield (PLQY) of 97% was achieved. More importantly, the YCl3 promoted CsPbI3 NRs with small aspect ratio of ~3.2 exhibit the PLQY of 84%, the highest value obtained from the red perovskite NRs. The fluorescence anisotropy of 0.184 mmol-YCl3 promoted CsPbI3 NRs is 0.38, and the rotational diffusion time τ rot = 1000 ns. The analysis on fluorescence anisotropy of the CsPbI3 perovskite NRs proves that the size in length and width is consistent with the result measured by TEM images of as-prepared perovskite NRs. Meanwhile, conductivities of the films made of 0.184 mmol-YCl3 promoted CsPbI3 NRs is 2.94 × 10−1 S/cm, which is 17 times higher than 1.70 × 10−2 S/cm of bare CsPbI3 nanocubes. Furthermore, various CsPbI3 NCs are employed to prepare light-emitting diodes (LEDs). The YCl3 promoted CsPbI3 NRs based LEDs display an optimum external quantum yield (EQE) of 10.5%, and luminance of 1672 cd/m2. These results prove that the as-prepared YCl3 promoted CsPbI3 NRs have promising prospect in optoelectronic devices.

Greenish-yellow emitting Ca9MgLi(PO4)7:Dy3+ phosphors – Photoluminescence and thermal stability

In this work, the photoluminescence features, decay lifetime, internal quantum yield, and thermal stability of whitlockite structured phosphors of Ca9MgLi(PO4)7:Dy3+ were investigated. The phosphor exhibit the capability of being efficiently excited by near-UV (350, 364, 387 nm) and blue light (451 nm), exhibiting the characteristic greenish-yellow emission with two strong peaks at 487 and 577 nm, ascribing to the transitions of 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. The phosphor synthesized using a conventional solid-state reaction method at 1350 °C also show high phase purity with good compositional homogeneity and crystallinity. The Ca9MgLi(PO4)7:0.1Dy3+ phosphor showed the optimal photoluminescence emission intensity and quantum yield. The electronic transition mechanism is direct exchange interaction between activators, contributing to the concentration quenching. The phosphor was able to retain 67% of its intensity without significant colour change at an elevated temperature up to 300 °C. This work illustrates the potential of Ca9MgLi(PO4)7:Dy3+ phosphors for the application in white LED devices pumped with an n-UV or blue-emitting chip.

Effective infrared emission of erbium ions doped inorganic lead halide perovskite quantum dots by sensitization of ytterbium ions

Abstract Rare earth ions doped all-inorganic lead halide perovskite quantum dots (PeQDs) have attracted extensive attention due to the rare earth ions doping greatly expanding the optical properties of PeQDs. Here, Er3+ and Yb3+ ions co-doped CsPbCl3 PeQDs are synthesized by the improved hot-injection method. The excitonic emission and near-infrared (NIR) IIb emission of Er3+ ions and quantum-cutting emission of Yb3+ ions were observed in CsPbCl3:Yb3+, Er3+ PeQDs. Interestingly, the NIR IIb emission of Er3+ ions is only obtained in PeQDs through the effective sensitization of Yb3+ ions. The energy transfer efficiency from Yb3+ to Er3+ ions is 23.5%. Furthermore, the optimal photoluminescence quantum yield (PLQY) of a NIR IIb emission for Er3+ ions was got by typical anion exchange reaction, and the value is up to 14.6%. This work provides a new way that further extends the emission wavelength of PeQDs to NIR IIb region, which will broaden the application scope of PeQDs.

Highly Luminescent and Stable Green Quasi‐2D Perovskite‐Embedded Polymer Sheets by Inkjet Printing

AbstractPerovskite materials serve as promising candidates for display and lighting due to their excellent optical properties, including tunable bandgaps and efficient luminescence. However, their efficiency and stability must be improved for further application. In this work, quasi‐two‐dimensional (quasi‐2D) perovskites embedded in different polymers are prepared by inkjet printing to construct any luminescent patterns/pictures on the polymer substrates. The optimized quantum yield reaches over 65% by polyvinyl‐chloride‐based quasi‐2D perovskite composites. In addition, as‐fabricated perovskite−polymer composites with patterns show excellent resistance to abrasion, moisture, light irradiation, and chemical erosion by various solvents. Both quantum yield and lifetime are superior to those reported to date. These achievements are attributed to the introduction of the PEA+cations to improve the luminance and stability of perovskite. This patterned composite can be useful for color‐conversion films with low cost and large‐scale fabrication.

White luminescent single-crystalline chlorinated graphene quantum dots.

A new class of white luminescent materials, white-light-emitting graphene quantum dots (WGQDs), have attracted increasing attention because of their unique features and potential applications. Herein, we designed and synthesized a novel WGQDs via a solvothermal molecular fusion strategy. The modulation of chlorine doping amount and reaction temperature gives the WGQDs a single-crystalline structure and bright white fluorescence properties. In particular, the WGQDs also exhibit novel and robust white phosphorescence performance for the first time. An optimum fluorescence quantum yield of WGQDs is 34%, which exceeds the majority of reported WGQDs and other white luminescent materials. The WGQDs display broad-spectrum absorption within almost the entire visible light region, broad full width at half maximum and extend their phosphorescence emission to the entire white long-wavelength region. This unique dual-mode optical characteristic of the WGQDs originates from the synergistic effect of low-defect and high chlorine-doping in WGQDs and enlarges their applications in white light emission devices, cell nuclei imaging, and information encryption. Our finding provides us an opportunity to design and construct more advanced multifunctional white luminescent materials based on metal-free carbon nanomaterials.

Zn defect-mediated Z-scheme electron-hole separation in AgIn5S8/ZnS heterojunction for enhanced visible-light photocatalytic hydrogen evolution

Exploring high-efficiency Z-scheme heterojunction photocatalyst has been regarded as an effective approach for promoting photocatalytic hydrogen production efficiency. In this study, a novel direct Z-scheme heterojunction composed of AgIn5S8 (denoted as AIS) and Zn-defective ZnS (denoted as D-ZnS) was fabricated via two-step hydrothermal method. The AIS/D-ZnS heterojunction exhibited improved visible light harvesting capability, prolonged charge lifetime and promoted charge separation efficiency, thus contributing to the remarkably enhanced photocatalytic activity as well as stability. The photocatalytic H2 evolution rate of the optimized (0.10:1)AIS/D-ZnS reached 932.76 μmol·h−1 g−1, which was 12 times higher than that of bare D-ZnS (75.13 μmol·h−1 g−1) under visible light irradiation, and an optimal apparent quantum yield of 3.7% was achieved at λ = 420 nm. TEM, XPS, EPR and PL results confirmed the appropriate concentration of Zn defects is conducive to the separation of photogenerated carriers. DMPO-EPR and PL probe experiments for determining O2− and OH active radicals further proved that the transfer and separation of electrons and holes followed Z-scheme mechanism. This work not only presents an alternative strategy for the construction of highly efficient Z-scheme heterojunction photocatalysts, but also provides new insights into the role of defects in mediating the separation and migration of charge carriers.

Ectopic expression of the Pseudomonas aeruginosa KatA gene in cotton improves its drought tolerance and yield under drought stress

Drought stress breaks the balance between the production and elimination of reactive oxygen species in plant cells, resulting in the accumulation of free radicals, which in turn affect plant growth, development, and yield. Antioxidant enzymes including catalase, can scavenge excessive free radicals and protect cells from oxidative damage. In this study, T0 transgenic cotton expressing a catalase gene PaKatA from Pseudomonas aeruginosa was obtained by Agrobacterium-mediated method, and two seventh generation of transgenic cotton lines were obtained by continuous screening for kanamycin resistance and PCR-based genotyping. Ectopic expression of PaKatA in cotton resulted in significantly elevated catalase and peroxidase activities, proline and relative water content, as well as decreased H2O2 and malondialdehyde content under drought stress conditions, conferring on transgenic plants better tolerance to drought. Furthermore, the yield of transgenic cotton increased by 34% under drought stress in the field, probably as a result of relatively stronger net photosynthetic capacity (Pn) and better optimal quantum yield of PSII (Fv/Fm). Our results indicate that the PaKatA gene can be used to improve drought tolerance and yield of cotton varieties and might also be a promising drought-resistant gene for improving other crop varieties.

Hyperspectral VNIR-spectroscopy and imagery as a tool for monitoring herbicide damage in wilding conifers

Wilding conifers, the naturally regenerated scions of exotic conifer species, are a major ecological and economic issue in New Zealand. Hyperspectral imagery could provide a useful means of monitoring the efficacy of wilding control measures but little research has examined this possibility. Data were collected from an experiment, that included thirty-nine young Pinus contorta (Douglas) trees allocated to a control and two herbicide treatments (triclopyr butoxyethyl ester and diquat dibromide monohydrate). The objectives of this research were to examine the temporal impacts of herbicide on needle discolouration, spectral properties and tree physiology and to develop models to predict photosynthetic parameters from hyperspectral data. In accordance with obvious discolouration on the first day after treatment, values of net photosynthesis rate (A), electron transport rate (ETR), stomatal conductance (G) and optimal quantum yield of photosystem II (Fv/Fm) declined rapidly for plants treated with diquat. Discolouration following application of triclopyr was not evident before the second week, and values of A, ETR, G and Fv/Fm declined slower than those of diquat. Of the tested narrow-band spectral indices calculated from needle spectra photochemical reflectance index (PRI) exhibited the strongest correlation with the four photosynthetic parameters and R2 values between PRI and A, Fv/Fm, ETR and G were, respectively, 0.53, 0.46, 0.68 and 0.29. Models that used raw spectra as inputs showed that sparse partial least squares (SPLS) outperformed the three other approaches tested (PLS, Support Vector Machines, Elastic Net) and R2 values using this approach for A, Fv/Fm, ETR and G were, respectively, 0.64, 0.62, 0.65 and 0.42.

The physiological and biochemical photosynthetic properties of Lycium ruthenicum Murr in response to salinity and drought

To estimate the salt tolerance and drought tolerance of Lycium ruthenicum Murr, we designed a pot experiment to measure the physiological and biochemical photosynthetic mechanisms of this species by establishing a range of NaCl concentrations (0, 50, 100, 200 and 400 mM) and degrees of drought stress (30%, 60%, 75% and 100% of field capacity). The results showed that the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), chlorophyll (Chl), carotenoids (Cars), maximal fluorescence (Fm), optimal quantum yield of photosystem II (PSII) (Fv/Fm), performance index (PIABS), activity of the water-splitting complex (Fv/Fo), actual photochemical efficiency of PSII (ΦPSII) and photochemical quenching (qP) were stimulated by moderate salinity (0–100 mM) and low water deficit (75–100%) and inhibited by high salinity (200–400 mM) and severe water deficit (30–60%). The changes in minimal fluorescence (Fo) and nonphotochemical quenching (qN) were opposite. Furthermore, the contents of malondialdehyde (MDA), proline, superoxide dismutase (SOD), and peroxidase (POD) significantly increased with increasing stress levels. In summary, salt and drought stress can separately enhance the photosynthetic capability to some extent because of increases in Gs and PSII activity. With an increase in stress, nonstomatal limitations, inhibition of electron transport and the activity of PSII can lead to reductions in photosynthetic capability. In addition, increases in osmotic substances and antioxidant enzymes can increase photosynthesis to some extent, but the physiological photosynthetic mechanisms are not protected from damage as these substances and enzymes continually increase. In summary, the resulting information can provide a theoretical basis and reference for construction of the ecological environment of the Qaidam area and the popularization and cultivation of Lycium ruthenicum Murr, thereby increasing ecological, social and economic benefits.

Narrow Band-Edge Photoluminescence of Ga3+-Doped AgInS2 Quantum Dots

Quantum dots (QDs) composed of multinary I-III-VI semiconductors and related materials exhibit unique composition- and size-dependent physicochemical properties and have attracted much attention for the application to luminescent devices, solar cells, and photocatalyts because of their strong absorption coefficient and low toxicity. It has been reported that the QDs composed of CuInS2, AgInS2 and their solid solution with ZnS exhibited strong photoluminescence (PL) in the visible light wavelength region, PL peak wavelength being tunable by controlling the particle size and composition. Most of these multinary QDs exhibited broad defect-site PL peaks with a large Stokes shift, which may limit large-scale commercial applications. In contrast, recently, we have reported that rod-shaped (AgIn)xZn2(1-x)Te2 QDs with almost stoichiometric composition exhibited a clear exciton peak in the absorption spectra and a narrow band-edge emission peak in the near-IR wavelength region, the peak wavelengths of which were blue-shifted with a decrease in the x value.(1) In this study, we synthesize non-stoichiometric Ag-In-Ga-S (AIGS) QDs and then investigate their PL properties in relation to their chemical compositions.(2,3) AIGS QDs were synthesized in a mixture solvent of oleylamine and dodecanethiol by the thermal decomposition of the precursor mixture of elemental sulfur, Ag(OAc), Ga(acac)3, and In(acac)3 at 300 oC for 10 min with vigorous stirring under an N2 atmosphere, in which the ratios of Ag/(Ag+In+Ga) and In/(In+Ga) were varied. By adding methanol to the resulting solution, the target AIGS nanoparticles were isolated as wet precipitates. GaSx shell coating was carried out by the heat treatment of AIGS QDs in oleylamine in the presence of Ga(acac)3 and thiourea. Stoichiometric AIGS QDs, which had Ag/(Ag+In+Ga)= 0.5, exhibited a broad defect-site PL peak with a small narrow band-edge PL peak. With a decrease in the Ag/(Ag+In+Ga) ratio, the intensity of band-edge peak was enlarged, being optimal at non-stoichiometric composition of Ag/(Ag+In+Ga)= ca. 0.4. The wavelength of band-edge PL peak was blue-shifted from 610 to 500 nm by decreasing the content of In in AIGS QDs from In/(In+Ga)= 1.0 to 0.2. The GaSx coating of AIGS QDs produced amorphous shell layer of ca. 1 nm thickness on AIGS core surface. Thus-obtained AIGS@GaSx core-shell particles predominantly exhibited a band-edge PL peak of 41 nm in FWHM, and then the intensity of broad defect-site peak was significantly reduced to less than 15 %. The optimal PL quantum yield of AIGS@GaSx core-shell QDs was 28% with green band-edge emission at 530 nm. The observed wavelength tunability of the band-edge PL peak will facilitate possible use of these toxic element-free I-III-VI-based QDs in a wide area of applications. Reference (1) T. Kameyama et al., J. Mater. Chem. C 2018, 6, 2034. (2) T. Uematsu et al., NPG Asia Materials 2018, 10, 713 (3) T. Kameyama et al., ACS Appl. Mater. Interfaces 2018 , 10, 42844.