High QY Research Articles

Formation mechanism of lignin-derived carbon quantum dots: From chemical structures to fluorescent behaviors

Biomass-derived carbon quantum dots (CQDs) have the advantage of being green and low-cost, but their complex structure makes the study of their formation mechanism encounter a bottleneck. Lignin-derived CQDs were prepared by a two-step process of “low-temperature liquid depolymerization” coupled with “hydrothermal reaction” in a mild organic acid system. In the first step of the low-temperature acidolysis process, the lignin polymer first undergoes deethering and depolymerization reactions. During the hydrothermal process in the second step, the organic small molecules on the surface of the supernatant are enriched with reactive groups that are dehydrated, condensed, crosslinked, and carbonized under high temperature and pressure to form CQDs. On the other hand, these activated large sp2 carbon domains in the oxidized solid residue from lignin acidolysis undergo hydrothermal cleavage under high-temperature and high-pressure conditions, followed by deoxygenation and eventual decomposition into small carbon domain CQDs products. Among them, the supernatant component C1 after lignin acidolysis with abundant N-H and C-OH reactive groups is targeted as a key precursor for the formation of lignin-derived CQDs, and the resulting CQDs have both the highest QY (19.5%) and yield (16.5%). This study bridges the research gap on the formation mechanism of biomass-derived CQDs and offers a reference for the sustainable preparation of biomass-derived CQDs.

In-situ synthesis of V2AlC@V2O5/TiO2 immobilized over honeycomb support with vanadium oxide electron transfer mediator for stimulating selective CO2 photoreduction through bi-reforming in a monolith reactor

Photocatalytic CO2 reduction to valuable chemicals and fuels is a practical approach for climate action; however, available photocatalysts and photoreactors are less efficient. In this work, well-designed V2AlC@V2O5 supported TiO2 and immobilized over honeycomb support for CO2 photoreduction in a monolith reactor have been investigated. The catalysts were loaded over the monolithic support using the sol-gel dip-coating method and found promising for higher light absorbance and charge separation. The performance of V2AlC@V2O5/TiO2 composite for photocatalytic CO2 reduction with water and bi-reforming of methanol was performed using a fixed bed and monolith photoreactor. Using V2AlC@V2O5/TiO2 with a fixed bed reactor and methanol–water mixture, a CO yield of 13.75 mmol g−1h−1 was produced, 26.39 and 38.19-fold higher than using water and pristine TiO2, respectively. Similarly, CH4 production was 1.97 and 12.33 folds higher than using water and TiO2 only, whereas, using water, production of H2 was not detected. The higher photoactivity of the composite with methanol was due to efficient photo-induced carrier separation due to the synergistic effect of V2AlC/V2O5 and more production of protons. Using a monolith photoreactor, CH4, CO and H2 production rates of 55.44, 35.51 and 1.638 mmol g−1h−1 were obtained, 166.50, 2.58 and 3.05 times more than those produced using a fixed bed reactor. This significantly higher photoactivity with monolith photoreactor was due to higher photon flux utilization with surface reactions, resulting in more production and utilization of photoinduced charge carriers. The highest QY after five consecutive cycles was 48.374, 25.358 and 1.51 % for CH4, CO and H2, which is 200.5, 2.54 and 3.87 folds higher than using the fixed bed, respectively. This work provides a new approach to designing and fabricating higher efficient and stable photocatalytic system for CO2 recycling, and it can be further employed for other energy-related applications.

High-brightness green InP-based QLEDs enabled by in-situ passivating core surface with zinc myristate

The performance of red InP and blue ZnTeSe-based quantum dots (QDs) and corresponding QD light emitting diodes (QLEDs) has already been improved significantly, whose external quantum efficiencies (EQEs) and luminances have exceeded 20% and 80 000 cd m−2, respectively. However, the inferior performance of the green InP-based device hinders the commercialization of full-color Cd-free QLED technology. The ease of oxidation of the highly reactive InP cores leads to high non-radiative recombination and poor photoluminescence quantum yield (PL QY) of the InP-based core/shell QDs, limiting the performance of the relevant QLEDs. Here, we proposed a fluoride-free synthesis strategy to in-situ passivate the InP cores, in which zinc myristate reacted with phosphine dangling bonds to form Zn–P protective layer and protect InP cores from the water and oxygen in the environment. The resultant InP/ZnSe/ZnS core/shell QDs demonstrated a high PL QY of 91%. The corresponding green-emitting electroluminescence devices exhibited a maximum EQE of 12.74%, along with a luminance of over 175 000 cd m−2 and a long T50@100 cd m−2 lifetime of over 20 000 h.

Eu3+ doped (Y0.75Sc0.25)2O3 red-emitting ceramics with excellent photoluminescence properties for LEDs

Developing narrow-band red-emitting ceramic phosphors with high quantum yield and low thermal quenching is vital for mid to high powder solid state lighting. In this study, a series of (Y0.75Sc0.25)2O3:Eu3+ ceramics were fabricated and their photoluminescence properties were studied. The spectral measurement suggests that the optimal doping concentration of Eu3+ is as high as 14%. The heavily doped samples show strong absorption in the NUV-blue region (particularly 360–420 nm and 460–475 nm), bright red emission dominated by the sharp peak located at 611 nm, CIE chromaticity coordinates close to the NTSC standard value of red emission, and single exponential photoluminescence decay without afterglow. In particular, ((Y0.75Sc0.25)0.86Eu0.14)2O3 ceramic exhibits high QY of 86.9%, high color purity of 96.9%, and low thermal quenching loss of 16% as the temperature increases from 300 to 570 K. The excellent photoluminescence properties highlight the great potential of Eu3+ heavily doped (Y0.75Sc0.25)2O3 red-emitting ceramics as color converters for solid state lighting, which is demonstrated by the outstanding electroluminescence performance of the fabricated red and white LEDs.

Tunable light emission of Bi and V-doped borosilicate glasses for application in white light-emitting diodes

Melt-quenched borosilicate glasses, co-doped with Bi and V ions, exhibited broad visible spectrum emissions. Bi ions primarily existed as Bi3+, acting as network modifiers, lowering the glass transition temperature linearly with increasing Bi content. V5+ ions adopted tetrahedral coordination as [VO4]3- units. Photoluminescence of Bi ions is shifted from blue to longer wavelengths with higher Bi content, associated with the stabilization of Bi2+ and the presence of Bi3+ in different local environments. Combined with V ions, the glasses emitted light covering the entire visible spectrum, offering the potential for white LED applications with correlated color temperatures ranging from 6135 to 4010 K. The highest QY was 11.9 and 8.0 % upon excitation at 325 and 340 nm.

A highly Mn2+-doped narrowband green phosphor toward wide color-gamut display applications

The highly doped phosphor La0.827Al11.9O19.09:Mn2+ exhibits intense green emission with a narrow FWHM, high PL QY and excellent thermal stability, which confer great potential for wide-color gamut LCD backlight applications.

Excited-State Odd-Even Effect in Through-Space Interactions.

The odd-even effect is a fantastic phenomenon in nature, which has been applied in diverse fields such as organic self-assembled monolayers and liquid crystals. Currently, the origin of each odd-even effect remains elusive, and all of the reported odd-even effects are related to the ground-state properties. Here, we discover an excited-state odd-even effect in the through-space interaction (TSI) of nonconjugated tetraphenylalkanes (TPAs). The TPAs with an even number of alkyl carbon atoms (C2-TPA, C4-TPA, and C6-TPA) show strong TSI, long-wavelength emission, and high QY. However, the odd ones (C1-TPA, C3-TPA, C5-TPA, and C7-TPA) are almost nonexistent with negligible QY. Systematically experimental and theoretical results reveal that the excited-state odd-even effect is synthetically determined by three factors: alkyl geometry, molecular movability, and intermolecular packing. Moreover, these flexible luminescent TPAs possess tremendous advantages in fluorescent information encryptions. This work extends the odd-even effect to photophysics, demonstrating its substantial importance and universality in nature.

The Role of the Amino Acid Molecular Characteristics on the Formation of Fluorescent Gold- and Silver-Based Nanoclusters.

Role of amino acids like L-phenylalanine (Phe), L-glutamine (Gln) and L-arginine (Arg) is described and interpreted in terms of their potential for preparation of fluorescent molecular-like gold and silver nanostructures. We are among the first to demonstrate the effect of syntheses conditions as well as the molecular characteristics of Phe, Gln and Arg amino acids on the structure of the formed products. Comprehensive optical characterizations (lifetime, quantum yield (QY%)) of the blue-emitting products were also carried out. It was confirmed that for all Au-containing samples and for Gln-Ag system the characteristic fluorescence originates from few-atomic metallic nanoclusters (NCs) where the reduction of metal ions was promoted by citrate in some cases. Relatively high QY% (∼18 %) was obtained for Arg-stabilized Au NCs due to the existence of an electrostatic interaction between the electron rich, positively charged guanidium side chain of Arg and the negatively charged carboxylate group of citrate on the metallic surface. Size and structural analysis of the products were evaluated by infrared measurements and dynamic light scattering techniques.

Metal-Ion-Doped Manganese Halide Hybrids with Tunable Emission for Advanced Anti-Counterfeiting.

Stimuli-responsive luminescent materials have received great attention for their potential application in anti-counterfeiting and information encryption. Manganese halide hybrids have been considered an efficient stimuli-responsive luminescent material due to their low price and adjustable photoluminescence (PL). However, the photoluminescence quantum yield (PLQY) of PEA2MnBr4 is relatively low. Herein, Zn2+- and Pb2+-doped PEA2MnBr4 samples are synthesized, and show an intense green emission and orange emission, respectively. After doping with Zn2+, the PLQY of PEA2MnBr4 is elevated from 9% to 40%. We have found that green emitting Zn2+-doped PEA2MnBr4 could transform to a pink color after being exposed to air for several seconds and the reversible transformation from pink to green was achieved by using heating treatment. Benefiting from this property, an anti-counterfeiting label is fabricated, which exhibits excellent "pink-green-pink" cycle capability. Pb2+-doped PEA2Mn0.88Zn0.12Br4 is acquired by cation exchange reaction, which shows intense orange emission with a high QY of 85%. The PL of Pb2+-doped PEA2Mn0.88Zn0.12Br4 decreases with increasing temperature. Hence, the encrypted multilayer composite film is fabricated relying on the different thermal responses of Zn2+- and Pb2+-doped PEA2MnBr4, whereby the encrypted information can be read out by thermal treatment.

Multicolor Photoluminescence from Nonconjugated Poly(3,4-dihydropyran) Nanoparticles

In recent years, nonconjugated organic luminophores are receiving considerable interest from the scientific community, offering a new conceptual basis for the development of alternative photoluminescence-based technologies. In this work, the polymerization of 3,4-dihydropyran was exploited for the preparation of nonconjugated photoluminescent polymer nanoparticles. Remarkably, excitation-dependent multicolor emission ranging from blue to yellow was observed in both solid and solution. In contrast with similar materials, this behavior was not attributed to aggregation-induced emission, but rather to the presence of independent, noninteracting chromophores located on the polymer structure. Structural and optical characterizations along with further chemical modifications suggest that the emission is related to the presence of acetal groups formed by ring-opening polymerization. In addition, it was shown that the removal of unsaturated structures could enhance the photoluminescence quantum yield of the polymer (QY) up to 0.20 (λex = 355 nm). This work provides a new type of nonconjugated organic luminophore with both high QY and multicolor emission.

Enhanced NIR fluorescence quantum yield of graphene quantum dots using dopants

In the present work, several efforts have been made theoretically to achieve an excellent non-toxic fluorescent graphene quantum dot (GQD) in the near-infrared region for the application of bio-imaging and sensing. Although the QY of GQDs is a maximum of 98.5% in the visible region, it is still very low, and it is as low as 7% in NIR. Sulfur and its group elements have been used for doping because they are pretty cheap and nontoxic and hence suitable for this application. The surface-doped position is considered for studying their effect on the energy band gap, absorption and fluorescence properties. The HOMO and LUMO isosurfaces have been analyzed in order to comprehend the nature of the dominant transition taking place in absorption spectra. Additionally, the quantitative indices, transition density matrix contour maps, and charge difference density have all been examined in order to determine whether this particular transition is locally excited or involves charge transfer. Following this, the QY of each GQD has been determined by considering the fluorescence spectra. The wavelength of fluorescence of doped GQDs is found to be in the region of 800–1400 nm, i.e. in NIR, which is strongly desirable for bio-imaging and bio-sensing applications. With a fluorescence of ∼850 nm, sulfur-doped GQDs (S-GQD: C52S2H18) have the greatest QY, 26%, which is larger than the 7% achieved earlier in NIR and such a high QY in NIR is being reported for the first time.

Ultra-stable CsPbBr3 nanocrystals encapsulated in mesoporous silica KIT-6 for LED applications

Metal halide perovskite nanocrystals (NCs) with strong absorption, high photoluminescence quantum yield (PL QY) and narrow bandwidth have shown great potential for display applications. However, their poor stability hinders their long-term device applications. Herein, we encapsulate CsPbBr3 NCs in closed-hole mesoporous silica KIT-6 through the facile high temperature solid reaction method. The obtained CsPbBr3@KIT-6 composites exhibit a high PL QY of 64% and a narrow bandwidth of 24 nm. Particularly, the collapsed mesoporous silica can protect the CsPbBr3 NCs from the impact of water or light irradiation. For instance, the PL QY of the NCs maintains 90% of the initial value after being immersed in water for 30 days. Ultimately, white-light-emitting diode (WLED) with a wide color gamut of 126.5% National Television System Committee (NTSC) standard was fabricated by packaging green-emitting CsPbBr3@KIT-6 powders, K2SiF6: Mn4+ red phosphor and blue diode chip. The WLED maintained 88% of its initial luminous efficacy after 30 days of operation, exhibiting good device stability.

Decyl disulfide surface treatment improved photoluminescence quantum yield and stability of blue-emitting CsPbBr3 nanoplatelets

Improving the photoluminescence quantum yields (PL QYs) and stability of blue-emitting CsPbBr3 nanoplatelets (NPLs) is essential for the application in high-quality displays. Herein, highly luminescent CsPbBr3 NPLs with PL peak at 462 nm were prepared by a modified supersaturated recrystallization synthesis strategy at room temperature. The resulting blue CsPbBr3 NPLs show high PL QY of 98% and a full width at half maximum of 13 nm, benefiting from the decyl disulfide (DF) surface treatment. Besides, the DF-treated CsPbBr3 NPLs show lower Urbach energy (15 meV) and more outstanding water, acetone, and UV-light resistance stabilities than the pristine ones, suggesting that the surface ligand treatment can reduce Br− vacancy defects and inhibit the non-radiative recombination process. Based on the temperature-dependent PL, the exciton binding energy of CsPbBr3 NPLs is found to increase from 109 to 201 meV after DF treatment. Finally, light-emitting diodes based on the treated CsPbBr3 NPLs were fabricated.

Photoluminescence properties of InP/GaP/ZnS core/shell/shell colloidal quantum dots treated with halogen acids

InP quantum dots (QDs) with low toxicity are considered to be the most promising materials. However, the oxidation problem of In and P has become to the major factor affecting the optical properties of InP QDs. In this work, the effect of luminescence properties of InP/GaP/ZnS QDs with halogen acid treatment have been studied. The results show that HF and HCl are beneficial to improve the optical properties of QDs, HBr especially HI are not conductive to promote the photoluminescence quantum yield (PL QY) of QDs. HF and HCl can etch the oxidative layer effectively, the F− and Cl− can also passivate the surface indium dangling bonds in the form of atomic ligands. The proposed model of charge carrier recombination show that the PL QY improved significantly after HA treatment attributed to the recombination of electron-hole pairs through radiative pathways mainly from the conduction band and valence band. The InP QDs with HF treatment has the best luminescence properties with high PL QY of 96%, offering great potential for advanced optoelectronic devices.

Lanthanide(III) Ions and 5-Methylisophthalate Ligand Based Coordination Polymers: An Insight into Their Photoluminescence Emission and Chemosensing for Nitroaromatic Molecules.

The work presented herein reports on the synthesis, structural and physico-chemical characterization, luminescence properties and luminescent sensing activity of a family of isostructural coordination polymers (CPs) with the general formula [Ln2(μ4-5Meip)3(DMF)]n (where Ln(III) = Sm (1Sm), Eu (2Eu), Gd (3Gd), Tb (4Tb) and Yb (5Yb) and 5Meip = 5-methylisophthalate, DMF = N,N-dimethylmethanamide). Crystal structures consist of 3D frameworks tailored by the linkage between infinite lanthanide(III)-carboxylate rods by means of the tetradentate 5Meip ligands. Photoluminescence measurements in solid state at variable temperatures reveal the best-in-class properties based on the capacity of the 5Meip ligand to provide efficient energy transfers to the lanthanide(III) ions, which brings intense emissions in both the visible and near-infrared (NIR) regions. On the one hand, compound 5Yb displays characteristic lanthanide-centered bands in the NIR with sizeable intensity even at room temperature. Among the compounds emitting in the visible region, 4Tb presents a high QY of 63%, which may be explained according to computational calculations. At last, taking advantage of the good performance as well as high chemical and optical stability of 4Tb in water and methanol, its sensing capacity to detect 2,4,6-trinitrophenol (TNP) among other nitroaromatic-like explosives has been explored, obtaining high detection capacity (with Ksv around 105 M-1), low limit of detection (in the 10-6-10-7 M) and selectivity among other molecules (especially in methanol).

Photo-induced structural and optical changes of CsPbBr3 perovskite nanocrystals in glasses

Cesium lead halide perovskite nanocrystals have particular optoelectronic properties and important applications in various fields. Embedding cesium lead halide perovskite nanocrystals into glass matrices have improved their thermal and chemical stabilities. However, these cesium lead halide perovskite nanocrystals in glasses are still sensitive to intense light irradiation, limiting their wide applications. In this work, fs laser irradiation on the structural and optical properties of cesium lead bromide (CsPbBr3) perovskite nanocrystals (PNCs) is investigated. It turns out that fs laser irradiation does not change the structural skeletons and band gap energies of CsPbBr3 PNCs in glasses, but induces surface Br vacancies. In-situ transient absorption spectral analysis reveals one <10 ps trapping process of photo-generated carriers after fs laser irradiation, and confirms that Br vacancies are induced by Br migration driven by photo-generated carriers. In addition, CsPbBr3 PNCs with high PL QY in glasses through Br passivation can be more easily damaged by fs laser, making it difficult to achieve stable stimulated emission towards laser application. These results shine light on the effect of halogen contents on the photo-stability of cesium lead halide PNCs and the regulation of cesium lead halide PNCs embedded glasses for photo-electronic applications.

Red-emitting carbon dots as luminescent agent in wide-range water detection in organic solvents and polarity-selective zebrafish imaging

Heteroatom-doped carbon dots with promising luminescent properties are excellent candidates for sensing and imaging applications. Herein, we reported a facile one-step hydrothermal synthesis of highly-fluorescent red-emitting carbon dots (R-CDs) with quantum yield of 37.2 %. R-CDs exhibit a maximum emission band at 640 nm under the excitation wavelength of 500 nm. Furthermore, R-CDs show excitation-dependent and solvent-engineered fluorescent characteristics that the luminescent properties could be greatly affected by polarity. Due to the sensitivity to polarity, a quick and precise approach for wide-range water detection in organic solvents has been developed. Because of the low autofluorescence background, R-CDs were applied to the zebrafish larvae imaging. Polarity-selective bright red light from R-CDs is seen in the low-polarity organs like yolk sac and eyes, which contain abundant lipids and lipoprotein. Our results demonstrate that R-CDs could be used as bio-imaging agents and fluorescent sensors for quantitative and visual water detection in various organic solvents. • High-fluorescent red-emitting carbon dots are synthesized from hydrothermal treatment of DMAB and boric acid. • Bright red emission at 640 nm (λ ex = 500 nm) and high QY of 37.2 % are achieved. • The variation of the emission intensity of R-CDs is highly dependent on solvent polarity. • Polarity-selective bright red light from R-CDs is seen in the low-polarity organs like yolk sac and eyes.

The NiO/CuInS2 Quantum Dots/ZnO Orderly Nanoarrays Transparent Pn Junction Towards Enhanced Photovoltaic Conversion via Dual Functional CuInS2 QDs

AbstractThe transparent pn junction of NiO/CuInS2 quantum dots (QDs)/ZnO orderly nanoarrays has been fabricated via a hybrid approach of sputtering‐hydrothermal‐chemical method. As revealed, the as‐prepared NiO/CuInS2 QDs/ZnO transparent pn junction exhibits decent transparency (≈85%), remarkable photovoltaic enhancement (≈2.5 × 103 folds, PCE of ≈1.19%) than that of intrinsic NiO/ZnO pn junction, and decent stability (4000s’ cycle), which is attributed to that the dual functional CuInS2 QDs with appropriate Fermi level, high QY, and wide bandgap, can optimize photogenerated carrier concentration‐mobility kinetic equilibrium efficiently, while maintaining a better transparency. Furthermore, the ZnO orderly nanoarrays can provide carrier transportation pathway, increase solar efficiency and physical stability.

Photoluminescence and structure evolution of laser synthesized ZrO2:Eu3+ nanopowders depending on the dopant concentration

Nanosized zirconia doped with europium (ZrO2:xEu3+, x = 0.07–9.95 wt%) and represented by weakly agglomerated spherical particles with the size of 9.7 ± 4.3 nm was synthesized by laser vaporization in an argon atmosphere using a cw CO2 laser. The specific surface area of the obtained nanoparticles is 92 ± 4 m2/g. The XRD study with Rietveld refinement revealed that the phase composition of the samples is represented predominantly by the tetragonal phase with a small content of monoclinic phase. At the concentrations above 4.57 wt%, stabilization of the cubic phase also occurs. The dependence of the PL intensity, PL lifetime, absolute quantum yield, and color coordinates of ZrO2:Eu3+ on the Eu concentration was studied. It was shown that the maximum PL intensity is observed at the concentration of 8.39 wt%. The Eu3+ lifetime decreases from 5.60 to 3.21 ms with a growth of the Eu content. Aging of the samples due to the adsorption of OH groups was revealed. The absolute quantum yield QY was measured for the 575–725 nm region corresponding to the luminescence of europium, and for the 410–725 nm region, which also includes the emission of oxygen vacancies. The QY was found to increase with the growth of Eu concentration, reaching the highest values for ZrO2:8.39Eu3+; it is equal to 1.6 and 17.6% for 575–725 and 410–725 nm regions, respectively. It was shown that variation of the Eu3+ concentration and excitation wavelength makes it possible to obtain color coordinates with red and close to white light. Along with the high QY for the region of 410–725 nm, this indicates that it is more promising to use ZrO2:Eu3+ as the white phosphor rather than the red one.

Synthesis of CdSe and CdSe/ZnS Quantum Dots with Tunable Crystal Structure and Photoluminescent Properties

Mastery over the structure of nanocrystals is a powerful tool for the control of their fluorescence properties and to broaden the range of their applications. In this work, the crystalline structure of CdSe can be tuned by the precursor concentration and the dosage of tributyl phosphine, which is verified by XRD, photoluminescence and UV-vis spectra, TEM observations, and time-correlated single photon counting (TCSPC) technology. Using a TBP-assisted thermal-cycling technique coupled with the single precursor method, core–shell QDs with different shell thicknesses were then prepared. The addition of TBP improves the isotropic growth of the shell, resulting in a high QY value, up to 91.4%, and a single-channel decay characteristic of CdSe/ZnS quantum dots. This work not only provides a facile synthesis route to precisely control the core–shell structures and fluorescence properties of CdSe nanocrystals but also builds a link between ligand chemistry and crystal growth theory.