Minimization of Energy Level Mismatch of PCBM and Surface Passivation for Highly Stable Sn-Based Perovskite Solar Cells by Doping n-Type Polymer.

Developing high-performance and stable Sn-based perovskite solar cells (PSCs) is difficult due to the inherent tendency of Sn2+ oxidation and, the huge energy mismatch between perovskite and Phenyl-C61-butyric acid methyl ester (PCBM), a frequently employed electron transport layer (ETL). This study demonstrates that perovskite surface defects can be passivated and PCBM's electrical properties improved by doping n-type polymer N2200 into PCBM. The doping of PCBM with N2200 results in enhanced band alignment and improved electrical properties of PCBM. The presence of electron-donating atoms such as S, and O in N2200, effectively coordinates with free Sn2+ to prevent further oxidation. The doping of PCBM with N2200 offers a reduced conduction band offset (from 0.38 to 0.21 eV) at the interface between the ETL and perovskite. As a result, the N2200 doped PCBM-based PSCs show an enhanced open circuit voltage of 0.79 V with impressive power conversion efficiency (PCE) of 12.98% (certified PCE 11.95%). Significantly, the N2200 doped PCBM-based PSCs exhibited exceptional stability and retained above 90% of their initial PCE when subjected to continuous illumination at maximum power point tracking for 1000 h under one sun.

Determining the optimal pharmacokinetic modelling and simplified quantification method of [18F]AlF-P16-093 for patients with primary prostate cancer (PPCa).

PURPOSE: This paper discusses the optimization of pharmacokinetic modelling and alternate simplified quantification method for [18F]AlF-P16-093, a novel tracer for in vivo imaging of prostate cancer. METHODS: Dynamic PET/CT scans were conducted on eight primary prostate cancer patients, followed by a whole-body scan at 60 min post-injection. Time-activity curves (TACs) were obtained by drawing volumes of interest for primary prostatic and metastatic lesions. Optimal kinetic modelling involved evaluating three compartmental models (1T2K, 2T3K, and 2T4K) accounting for fractional blood volume (Vb). The simplified quantification method was then determined based on the correlation between the static uptake measure and total distribution volume (Vt) obtained from the optimal pharmacokinetic analysis. RESULTS: In total, 17 intraprostatic lesions, 10 lymph nodes, and 36 osseous metastases were evaluated. Visually, the contrast of the tumor increased and showed the steepest incline within the first few minutes, whereas background activity decreased over time. Full pharmacokinetic analysis revealed that a reversible two-compartmental (2T4K) model is the preferred kinetic model for the given tracer. The kinetic parameters K1, k3, Vb, and Vt were all significantly higher in lesions when compared with normal tissue (P < 0.01). Several simplified protocols were tested for approximating comprehensive dynamic quantification in tumors, with image-based SURmean (the ratio of tumor SUVmean to blood SUVmean) within the 28-34 min window found to be sufficient for approximating the total distribution Vt values (R2 = 0.949, P < 0.01). Both Vt and SURmean correlated significantly with the total serum prostate-specific antigen (tPSA) levels (P < 0.01). CONCLUSIONS: This study introduced an optimized pharmacokinetic modelling approach and a simplified acquisition method for [18F]AlF-P16-093, a novel PSMA-targeted radioligand, highlighting the feasibility of utilizing one static PET imaging (between 30 and 60 min) for the diagnosis of prostate cancer. Note that the image-derived input function in this study may not reflect the true corrected plasma input function, therefore the interpretation of the associated kinetic parameter estimates should be done with caution.

Size-Regulated Hole and Triplet Energy Transfer from CdSe Quantum Dots to Organic Acceptors for Enhancing Singlet Oxygen Generation.

Triplet energy transfer (TET) from semiconductor quantum dots (QDs) is an emerging strategy for sensitizing molecular triplets that have great potential in many applications. Here, CdSe QDs with varying sizes and 1-pyrenecarboxylic acid (PCA) are selected as the triplet donor and acceptor, respectively, to study the TET and charge transfer dynamics as well as enhanced singlet oxygen (1O2) generation properties. The results from static and transient spectroscopy measurements demonstrate that both the TET and hole transfer occur at the QDs-PCA interface. The observed significant drop in TET efficiency from 52 to 8% with increasing QD size results from the reduced TET driving force between the QDs and PCA, which is further confirmed by the more efficient sensitization of the anthracene derivative with a large TET driving force. In contrast, the hole transfer efficiency displays a small decrease with an increasing QD size due to a slight change in the hole driving force. The sensitized PCA triplets show a good ability of 1O2 generation, and the 1O2 formation rate increases 10-fold as the QD size decreases from 3.3 to 2.4 nm. These findings provide a profound understanding of the TET and hole transfer mechanism from QDs to molecules and are significant in designing efficient 1O2 generation systems based on semiconductor QDs and triplet molecules.

Triplet generation at the CdTe quantum dot/anthracene interface mediated by hot and thermalized electron exchange for enhanced production of singlet oxygen.

Triplet energy transfer (TET) from semiconductor quantum dots (QDs) to molecular triplets has potential applications in photon up-conversion and singlet oxygen generation. Here, we have constructed a complex consisting of CdTe QDs as the donor and 9-anthracenecarboxylic acid (ACA) as the triplet acceptor, and studied the TET pathways and enhanced singlet oxygen generation properties. The results from steady-state and time-resolved spectroscopy demonstrate efficient TET with a total efficiency of over 80% from photoexcited CdTe QDs to ACA. Dynamical analysis clearly indicates two distinctive TET channels - hot electron exchange and thermalized electron exchange - mediating the TET process in the CdTe QDs-ACA complex. The TET efficiencies from hot electron exchange at high energetic levels and thermalized electron exchange on the lowest exciton state can reach ∼27% and ∼85%, respectively, following 530 nm excitation. This efficient TET endows the CdTe QDs-ACA complex with a good capability of generating singlet oxygen species with a yield of up to ∼59%. These findings contribute further insights to the mechanisms of interfacial TET processes and are significant in designing efficient TET systems based on semiconductor nanoparticles and triplet molecules.

Ion Co-storage in Porous Organic Frameworks through On-site Coulomb Interactions for High Energy and Power Density Batteries.

Fast and continuous ion insertion is blocked in the common electrodes operating with widely accepted single-ion storage mechanism, primarily due to Coulomb repulsion between the same ions. It results in an irreconcilable conflict between capacity and rate performance. Herein, we designed a porous organic framework with novel multiple-ion co-storage modes, including PF6 - /Li+ , OTF- /Mg2+ , and OTF- /Zn2+ co-storage. The Coulomb interactions between cationic and anionic carriers in the framework can significantly promote electrode kinetics, by rejuvenating fast ion carrier migration toward framework interior. Consequently, the framework via PF6 - /Li+ co-storage mode shows a high energy density of 878 Wh kg-1 cycled more than 20 000 cycles, with an excellent power density of 28 kW kg-1 that is already comparable to commercial supercapacitors. The both greatly improved energy and power densities via the co-storage mode may pave a way for exploring new electrodes that are not available from common single-ion electrodes.

Highly enhanced nonlinear optical absorption with ultrafast charge transfer of reduced graphene oxide hybridized by an azobenzene derivative.

Graphene-based materials have been attracted many attentions due to their excellent properties and potential applications in many fields. Graphene also provides a flexible substrate to develop novel functional materials by hybridizing with other organic or inorganic components. Herein, we report the functionalization of reduced graphene oxide (RGO) with an azobenzene derivative (BNB-t8) containing the π-conjugated moiety and hydrogen bonding groups, to improve the optical and nonlinear optical properties of RGO. With the introducing of BNB-t8, a new absorption band is formed and dominates the absorption spectrum, clearly demonstrates that the BNB-t8 has been hybridized with RGO, by combining the analysis of Raman and XRD data. Femtosecond Z-scan results present a highly enhanced saturable optical absorption of BNB-t8/RGO hybrid compared with that of RGO. By optimizing the hybridization ratio of BNB-t8 to RGO, the saturable absorption coefficient of BNB-t8/RGO hybrid reaches to -237 m/W, 38 times larger than that of RGO (-6.2 m/W). In the meantime, the third-order susceptibility χ(3) of BNB-t8/RGO hybrid is aslo enhanced by 8 times to be 5.18×10-13 esu. These enhancements of nonlinear optical properties of BNB-t8/RGO hybrid mainly arise from the charge transfer from RGO to BNB-t8. Femtosecond transient absorption measurements reveal that the charge separation takes place in 0.28 ps and the charge recombination in 2.0 ps, indicating a strong electron coupling and thus an enhanced electron delocalization in BNB-t8/RGO hybrid compared with those in RGO. We suggest that the noncovalent π-π interaction plays the dominant role for enhancing the electron delocalization of RGO after hybridizing with BNB-t8, while the hydrogen bonding interaction reinforce the coupling interaction between BNB-t8 and RGO moieties in the hybrid. The as-prepared BNB-t8/RGO hybrid with high saturable absorption coefficient with an ultrafast response presents a potential candidate as saturable absorber of mode-locked laser.

Probing the Electron Transfer between iLOV Protein and Ag Nanoparticles.

Nanomaterials have been widely used in biomedical sciences; however, the mechanism of interaction between nanoparticles and biomolecules is still not fully understood. In the present study, we report the interaction mechanism between differently sized Ag nanoparticles and the improved light-oxygen-voltage (iLOV) protein. The steady-state and time-resolved fluorescence results demonstrated that the fluorescence intensity and lifetime of the iLOV protein decreased upon its adsorption onto Ag nanoparticles, and this decrease was dependent upon nanoparticle size. Further, we showed that the decrease of fluorescence intensity and lifetime arose from electron transfer between iLOV and Ag nanoparticles. Moreover, through point mutation and controlled experimentation, we demonstrated for the first time that electron transfer between iLOV and Ag nanoparticles is mediated by the tryptophan residue in the iLOV protein. These results are of great importance in revealing the function of iLOV protein as it applies to biomolecular sensors, the field of nano-photonics, and the interaction mechanism between the protein and nanoparticles.

Serpentine Ni3 Ge2 O5 (OH)4 Nanosheets with Tailored Layers and Size for Efficient Oxygen Evolution Reactions.

Layered serpentine Ni3 Ge2 O5 (OH)4 is compositionally active and structurally favorable for adsorption and diffusion of reactants in oxygen evolution reactions (OER). However, one of the major problems for these materials is limited active sites and low efficiency for OER. In this regard, a new catalyst consisting of layered serpentine Ni3 Ge2 O5 (OH)4 nanosheets is introduced via a controlled one-step synthetic process where the morphology, size, and layers are well tailored. The theoretical calculations indicate that decreased layers and increased exposure of (100) facets in serpentine Ni3 Ge2 O5 (OH)4 lead to much lower Gibbs free energy in adsorption of reactive intermediates. Experimentally, it is found that the reduction in number of layers with minimized particle size exhibits plenty of highly surface-active sites of (100) facets and demonstrates a much enhanced performance in OER than the corresponding multilayered nanosheets. Such a strategy of tailoring active sites of serpentine Ni3 Ge2 O5 (OH)4 nanosheets offers an effective method to design highly efficient electrocatalysts.

Exocytosis of gold nanoparticle and photosensitizer from cancer cells and their effects on photodynamic and photothermal processes.

We first illustrate the faster decrease of the photothermal (PT) effect with the delay time of laser treatment, in which the illumination of a 1064 nm laser effectively excites the localized surface plasmon (LSP) resonance of cell-up-taken gold nanoring (NRI) linked with a photosensitizer (PS), when compared with the photodynamic (PD) effect produced by the illumination of a 660 nm laser for effective PS excitation. The measurement results of the metal contents of Au NRI and PS based on inductively coupled plasma mass spectroscopy and the PS fluorescence intensity based on flow cytometry show that the linkage of NRI and PS is rapidly broken for releasing PS through the effect of glutathione in lysosome after cell uptake. Meanwhile, NRI escapes from a cell with a high rate such that the PT effect decays fast while the released PS can stay inside a cell longer for producing a prolonged PD effect. The effective delivery of PS through the linkage with Au NRI for cell uptake and the advantageous effect of LSP resonance at a PS absorption wavelength on the PD process are also demonstrated.

Enhancements of Cancer Cell Damage Efficiencies in Photothermal and Photodynamic Processes through Cell Perforation and Preheating with Surface Plasmon Resonance of Gold Nanoring.

The methods of cell perforation and preheating are used for increasing cell uptake efficiencies of gold nanorings (NRIs), which have the localized surface plasmon resonance wavelength around 1064 nm, and photosensitizer, AlPcS, and hence enhancing the cell damage efficiency through the photothermal (PT) and photodynamic (PD) effects. The perforation and preheating effects are generated by illuminating a defocused 1064-nm femtosecond (fs) laser and a defocused 1064-nm continuous (cw) laser, respectively. Cell damage is produced by illuminating cell samples with a focused 1064-nm cw laser through the PT effect, a focused 1064-nm fs laser through both PT and PD effects, and a focused 660-nm cw laser through the PD effect. Under various conditions with and without cell wash before laser illumination, through either perforation or preheating process, cell uptake and hence cell damage efficiencies can be enhanced. Under our experimental conditions, perforation can be more effective at enhancing cell uptake and damage when compared with preheating.

Cancer cell death pathways caused by photothermal and photodynamic effects through gold nanoring induced surface plasmon resonance.

The different death pathways of cancer cells under the conditions of the photothermal (PT), effect, photodynamic (PD) effect, and their combination are evaluated. By incubating cells with Au nanoring (NRI) either linked with the photosensitizer, AlPcS, or not, the illumination of a visible continuous laser for exciting the photosensitizer or an infrared femtosecond laser for exciting the localized surface plasmon resonance of Au NRI, leads to various PT and PD conditions for study. Three different staining dyes are used for identifying the cell areas of different damage conditions at different temporal points of observation. The cell death pathways and apoptotic evolution speeds under different cell treatment conditions are evaluated based on the calibration of the threshold laser fluences for causing early-apoptosis (EA) and necrosis (NE) or late-apoptosis (LA). It is found that with the PT effect only, strong cell NE is generated and the transition from EA into LA is faster than that caused by the PD effect when the EA stage is reached within 0.5 h after laser illumination. By combining the PT and PD effects, in the first few hours, the transition speed becomes lower, compared to the case of the PT effect only, when both Au NRIs internalized into cells and adsorbed on cell membrane exist. When the Au NRIs on cell membrane is removed, in the first few hours, the transition speed becomes higher, compared to the case of the PD effect only.

Ce-Doped SnO2 Electron Transport Layer for Minimizing Open Circuit Voltage Loss in Lead Perovskite Solar Cells.

In the planar heterostructure of perovskite-based solar cells (PSCs), tin oxide (SnO2) is a material that is often used as the electron transport layer (ETL). SnO2 ETL exhibits favorable optical and electrical properties in the PSC structures. Nevertheless, the open circuit voltage (VOC) depletion occurs in PSCs due to the defects arising from the high oxygen vacancy on the SnO2 surface and the deeper conduction band (CB) energy level of SnO2. In this research, a cerium (Ce) dopant was introduced in SnO2 (Ce-SnO2) to suppress the VOC loss of the PSCs. The CB minimum of SnO2 was shifted closer to that of the perovskite after the Ce doping. Besides, the Ce doping effectively passivated the surface defects on SnO2 as well as improved the electron transport velocity by the Ce-SnO2. These results enabled the power conversion efficiency (PCE) to increase from 21.1% (SnO2) to 23.0% (Ce-SnO2) of the PSCs (0.09 cm2 active area) with around 100 mV of improved VOC and reduced hysteresis. Also, the Ce-SnO2 ETL-based large area (1.0 cm2) PSCs delivered the highest PCE of 22.9%. Furthermore, a VOC of 1.19 V with a PCE of 23.3% was demonstrated by Ce-SnO2 ETL-based PSCs (0.09 cm2 active area) that were treated with 2-phenethylamine hydroiodide on the perovskite top surface. Notably, the unencapsulated Ce-SnO2 ETL-based PSC was able to maintain above 90% of its initial PCE for around 2000 h which was stored under room temperature condition (23-25 °C) with a relative humidity of 40-50%.

Heteroatom Doping Promoted Ultrabright and Ultrastable Photoluminescence of Water-Soluble Au/Ag Nanoclusters for Visual and Efficient Drug Delivery to Cancer Cells.

Photoluminescence (PL) metal nanoclusters (NCs) have attracted extensive attention due to their excellent physicochemical properties, good biocompatibility, and broad application prospects. However, developing water-soluble PL metal NCs with a high quantum yield (QY) and high stability for visual drug delivery remains a great challenge. Herein, we have synthesized ultrabright l-Arg-ATT-Au/Ag NCs (Au/Ag NCs) with a PL QY as high as 73% and excellent photostability by heteroatom doping and surface rigidization in aqueous solution. The as-prepared Au/Ag NCs can maintain a high QY of over 61% in a wide pH range and various ionic environments as well as a respectable resistance to photobleaching. The results from structure characterization and steady-state and time-resolved spectroscopic analysis reveal that Ag doping into Au NCs not only effectively modifies the electronic structure and photostability but also significantly regulates the interfacial dynamics of the excited states and enhances the PL QY of Au/Ag NCs. Studies in vitro indicate Au/Ag NCs have a high loading capacity and pH-triggered release ability of doxorubicin (DOX) that can be visualized from the quenching and recovery of PL intensity and lifetime. Imaging-guided experiments in cancer cells show that DOX of Au/Ag NCs-DOX agents can be efficiently delivered and released in the nucleus with preferential accumulation in the nucleolus, facilitating deep insight into the drug action sites and pharmacological mechanisms. Moreover, the evaluation of anticancer activity in vivo reveals an outstanding suppression rate of 90.2% for mice tumors. These findings demonstrate Au/Ag NCs to be a superior platform for bioimaging and visual drug delivery in biomedical applications.

Unraveling the Nanoscale Segregation Mechanism in N-Doped Niobium for Enhanced SRF Performance.

The nitrogen doping (N-doping) treatment for niobium superconducting radio-frequency (SRF) cavities is one of the key enabling technologies that support the development of more efficient future large accelerators. However, the N-doping results have diverged due to a complex chemical profile under the nitrogen-doped surface. Particularly, under industrial-scale production conditions, it is difficult to understand the underlying mechanism thus hindering performance improvement. Herein, a combination of spatially resolved and surface-sensitive approaches is employed to establish the detailed near-surface phase composition of thermally processed niobium. The results show that intermediate phase segregations, particularly the nanometric carbon-rich phase, can impede the nitridation process and limit the interactions between nitrogen and the niobium sub-surface. In comparison, the removal of the carbon-rich layer at the Nb surface leads to enhanced nitrogen binding at the Nb surface. Combining the RF test results, it is shown that the complex uniformity and grain boundary penetrations of impurity elements have a direct correlation with the mid-field quench behavior in the N-doped Nb cavities. Therefore, proper control of the nanometric intermediate phase formation in discrete thermal steps is critical in improving the ultimate performance and production yield of the Nb cavities.

Inhibition of Sn2+ Oxidation in FASnI3 Perovskite Precursor Solution and Enhanced Stability of Perovskite Solar Cells by Reductive Additive.

Tin-based halide perovskite solar cells (Sn-PSCs) have attracted a progressive amount of attention as a potential alternative to lead-based PSCs (Pb-PSCs). Sn-perovskite films are fabricated by a solution process spin-coating technique. However, the efficiency of these devices varies significantly with the different batches of precursor solution due to the poor chemical stability of SnI2-DMSO and the oxidation of Sn2+ to Sn4+. This study investigated the origin of Sn2+ oxidation before film formation, and it was identified that the ionization of SnI2 in dimethyl sulfoxide (DMSO) causes the oxidation of free Sn2+ and I- ions. To address these issues, this study introduces the reductive additive 4-fluorophenylhydrazine hydrochloride (4F-PHCl) in the FASnI3 perovskite precursor solution. The hydrazine functional (-NH-NH2) group converted detrimental Sn4+ and I2 defects back to Sn2+ and I- in precursor solution while retaining the properties of the perovskite solution. Furthermore, the addition of 4F-PHCl in the precursor solution effectively slows the crystallization process, enhancing the crystallinity of FASnI3 perovskite films and guaranteeing the Sn2+/I- stoichiometric ratio, ultimately leading to a power conversion efficiency (PCE) of 10.86%. The hydrophobic fluorinated benzene ring in 4F-PHCl ensures moisture stability in perovskite films, allowing unencapsulated PSCs to retain over 92% of their initial PCE in an N2-filled glovebox for 130 days. Moreover, the 4F-PHCl-modified encapsulated PSCs showed superior operational stability for 420 h and maintained 95% of their initial PCE for 300 h under maximum power point tracking at 1 sun continuous illumination. This study's findings provide a promising pathway to create a controlled Sn-based perovskite precursor solution for highly reproducible and stable Pb-free Sn-PSCs.

Primary seminal vesicle adenocarcinoma with a history of seminal vesicle cyst: A case report and review of literature.

BACKGROUND: Primary seminal vesicle adenocarcinoma is a rare malignancy that is difficult to diagnose. CASE SUMMARY: A 54-year-old man with an 18-year history of a seminal vesicle cyst presented with worsening hematospermia that had persisted for one month. Dynamic contrast-enhanced computed tomography and pelvic magnetic resonance imaging indicated a mass with a cystic-solid component. Robot-assisted seminal vesicle tumor resection was performed, and primary seminal vesicle adenocarcinoma was confirmed pathologically. The patient received pelvic radiotherapy for six weeks, and to date, no evidence of recurrence has been found. CONCLUSION: Seminal vesicle cysts should be monitored long-term. Seminal vesicle adenocarcinoma presents with non-specific symptoms and can be diagnosed by immunohistochemistry.

Immunotherapy in SMARCB1 (INI-1)-deficient sinonasal carcinoma: Two case reports.

BACKGROUND: SMARCB1/INI-1 deficient sinonasal carcinoma (SDSC) is a rare subset of sinonasal undifferentiated carcinoma with a poor prognosis. Here, we present two case reports of SDSC patients. We also review the literature on this tumor. This is the first published report of SDSC treatment with immunotherapy. CASE SUMMARY: Here we present two patient cases of SDSC in which initial consultation and diagnosis were complicated but SDSC was ultimately diagnosed. One patient received a traditional treatment of surgery and adjuvant chemoradiotherapy, while the other patient received additional immunotherapy; the prognoses of these two patients differed. We review previous diagnostic literature reports and SDSC treatments and provide a unique perspective on this rare type of tumor. CONCLUSION: SDSC is a rare, diagnostically challenging carcinoma with a consistently poor prognosis, early distant metastases, and frequent recurrence. Timely diagnosis and intervention are critical for treatment, for which the standard of care is surgery followed by adjuvant chemoradiotherapy, though immunotherapy may be an effective new treatment for SDSC.

Suppressed Blinking and Polarization-Dependent Emission Enhancement of Single ZnCdSe/ZnS Dot Coupled with Au Nanorods.

Fluorescent quantum dots (QDs) have attracted extensive attention because of their promising applications in many fields such as quantum optics, optoelectronics, solid-state lighting, and bioimaging. However, photo-blinking, low emission efficiency, and instability are the drawbacks of fluorescent QD-based devices, affecting their optical properties and practical applications. Here, we report suppressed blinking, enhanced radiative rate, and polarization-dependent emission properties of single ZnCdSe/ZnS QDs assembled on the surface of Au nanorods (NRs). We found that the local surface plasmon (LSP) of Au NRs significantly regulates the excitation and emission properties of the composite ZnCdSe/ZnS QD-Au NRs (QD-Au NRs). The average number of photons emitted per unit time from single QD-Au NRs has been significantly enhanced compared with that of single ZnCdSe/ZnS QDs on the coverslip, accompanied by a drastically shortened lifetime and suppressed blinking. According to the experimental and simulation analysis, the photogenerated LSP field of Au NRs remarkably increases the excitation transition and the radiative rates of QD-Au NRs. Although the emission efficiency is slightly increased, the synergetic enhancement of excitation and radiative rates sufficiently competes with the nonradiative process to compensate for the low emission efficiency of QDs and ultimately suppress the photo-blinking of QD-Au NRs. Moreover, the polarization-dependent emission enhancement has also been observed and theoretically analyzed, demonstrating good consistency and confirming the contribution of excitation enhancement. Our findings present a practical strategy to improve the optical properties and stability of single QD-Au NR composite and provide essential information for a deep understanding of the interaction between emitters and the LSP field of metal nanoparticles.

Excellent Multiphoton Excitation Fluorescence with Large Multiphoton Absorption Cross Sections of Arginine-Modified Gold Nanoclusters for Bioimaging.

Fluorescent gold nanoclusters (Au NCs) with excellent one-photon and multiphoton properties have been demonstrated as promising candidates in many application fields. However, small multiphoton absorption (MPA) cross sections and weak multiphoton excitation (MPE) fluorescence impede their practical applications under near-infrared (NIR) excitation for biological imaging. Here, we report the regulated one-photon and multiphoton properties and mechanisms of arginine-stabilized 6-aza-2-thiothymine Au NCs (Arg/ATT-Au NCs) and the applications for MPE fluorescence imaging. The introduction of arginine into the capping layer of ATT-Au NCs significantly modifies the electronic structure, the absorption cross sections, and the relaxation dynamics of the lowest excited state, drastically reducing the nonradiative relaxation, suppressing the blinking, and greatly enhancing the fluorescence. Besides the improved one-photon properties, Arg/ATT-Au NCs demonstrate remarkable MPE fluorescence with a large MPA cross section. The two-photon (λex = 850 nm), three-photon (λex = 1400 nm), and four-photon (λex = 1700 nm) absorption cross sections have been determined to be 6.1 × 10-47 cm4 s1 photon-1, 1.5 × 10-78 cm6 s2 photon-2, and 5.5 × 10-108 cm8 s3 photon-3, respectively, much higher than those of conventional organic compounds and previously reported Au NCs. Moreover, Arg/ATT-Au NCs have been successfully applied in two-photon and three-photon excitation fluorescence imaging of living cells with NIR excitation. The manifold advantages of small size, high quantum yield, suppressed blinking, good photostability and cytocompatibility, large MPA cross sections, and excellent MPE fluorescence imaging performances make fluorescent Arg/ATT-Au NCs a great candidate of imaging probes with vis-NIR excitation.

Broadened optical absorption, enhanced photoelectric conversion and ultrafast carrier dynamics of N, P co-doped carbon dots.

Carbon dots (CDs) have attracted extensive attention for their unique properties and promising applications in many fields. Many efforts have been made to improve the optical and physicochemical properties of CDs using an atomic doping strategy; however, the photoelectric properties of CD-based devices have been less studied and the photocurrent density is far from satisfactory for practical operation. Deep understanding of the doping effects on the electronic structure and photophysical properties of CDs is fundamental and essential for effectively improving the optical and photoelectrical performance of CD-based devices. Here, we have synthesized nitrogen (N) and phosphorus (P) co-doped CDs (N, P-CDs) through a one-step hydrothermal approach, and systematically investigated the effects of P-dopants on the improved optical and photoelectric properties of N, P-CDs. The introduction of P atoms into N-CDs significantly changes the electronic structure and extends the absorption spectral region, enhancing the light-harvesting ability of N, P-CDs. Meanwhile, the regulated carrier dynamics have been investigated using time-resolved fluorescence and transient absorption spectroscopy. We found that the carrier recombination was decreased with introducing P atoms, and the photogenerated electrons in the higher excited states could be efficiently transferred to the lowest excited state. Moreover, the photocurrent density of N, P-CDs was increased by twelve times compared with that of N-CDs. Therefore, the effective doping of P atoms can significantly regulate the electronic structure, optical properties, carrier dynamics and photoelectric conversion of N, P-CDs. The achieved broadband light-harvesting, good photoelectric properties and photostability of the as-prepared N, P-CDs demonstrate an important example of P-doping to improve the optical and photoelectrical properties of CD-based devices.