Upconversion Fluorescence Properties Research Articles

Core-shell structured carbon dots with up-conversion fluorescence and photo-triggered nitric oxide-releasing properties.

Cancer-targeted nanotechnology has a new trend in the design and preparation of new materials with functions for imaging and therapeutic applications simultaneously. As a new type of carbon nanomaterial, the inherent core-shell structured carbon dots (CDs) can be designed to provide a modular nanoplatform for integration of bioimaging and therapeutic capabilities. Here, core-shell structured CDs are designed and synthesized from levofloxacin and arginine and named Arg-CDs, in which levofloxacin-derived chromophores with up-conversion fluorescence are densely packed into the carbon core while guanidine groups are located on the shell, providing nitric oxide (NO) for photodynamic therapy of tumors. Moreover, the chromophores in the carbon core irradiated by visible LED light generate large amounts of reactive oxygen species (ROSs) that will oxidize the guanidine groups located on the shell of the Arg-CDs and further increase the NO releasing capacity remarkably. The as-synthesized Arg-CDs show excellent biocompatibility, bright up-conversion fluorescence, and a light-controlled ROS & NO releasing ability, which can be a potential light-modulated nanoplatform to integrate bioimaging and therapeutic functionalities.

Synergetic assembly of a molybdenum disulfide/carbon quantum dot heterojunction with enhanced light absorption and electron transfer di-functional properties for photocatalysis

Cocatalysts play important roles in enhanced efficiency of heterojunctions that their selection and synthesis are essential. Carbon quantum dots (CQDs), as one of important cocatalysts, often suffer from complicated synthesis, low functionality, and low photocatalytic efficiency issues that need to be solved effectively. In this study, we constructed a new molybdenum disulfide/N,S-doped carbon quantum dots (MoS2/N,S-CQDs) heterojunction with enhanced light absorption and electrons transfer di-functional properties via a facile one-pot hydrothermal method. The MoS2/N,S-CQDs simultaneously degraded 99.8% of methylene blue (MB) and 95.1% of malachite green (MG) in an actual water system (Tianjin Lake) under simulated sunlight irradiation for 120 min. The heterojunction showed obvious efficiencies under both infrared light (degraded 83.8% of MG after 120 min) and visible light (90.1% MG after 120 min) irradiation. According to energy level and density functional theory (DFT) analyses, the electrons in MoS2/N,S-CQDs were demonstrated that transferred from N,S-CQDs to MoS2 interfaces, and the light-absorption range of the composites was effectively extended to near-infrared ranges owing to excellent up-conversion fluorescence property of the N,S-CQDs. We believe that the facile synthetic technique and effective multifunctional properties of composite have the potential for further research on CQDs-based heterojunctions and their industrial applications.

Nitrogen-doped carbon dots for doxorubicin-targeted delivery and two-photon cell imaging

Nitrogen (N) doped CDs (N-CDs) were prepared using citric acid and hexamethylenetetramine by a one-step hydrothermal method, characterized by transmission electron microscopy (TEM), Powder X-ray Diffractometer (PXRD), Nuclear Magnetic Resonance (13C NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and ultraviolet–visible (UV–vis) absorption spectra. The doping mechanism and drug-loading characteristics of N-CDs were also studied. The results showed that N-CDs had both down- and up-conversion fluorescence properties and the average particle size was about 4.28 nm. N-CDs could be used as a drug carrier for doxorubicin (DOX) (N-CDs-DOX) via the formation of the NC bond, and the drug-loading rate of N-CDs-DOX was 35.88%. The N-CDs-DOX had pH-targeted properties and low cytotoxicity. In vitro release of N-CDs-DOX belonged to the Weibull model and Fick diffusion. The results showed that N-CDs could deliver DOX successfully, and collocate with DOX in the SH-SY5Y cells through two-photon imaging. The N-CDs-DOX system had sustained-release and pH-targeted properties. N-CDs were expected to deliver a type of drugs containing CO group and be used in cancer treatment.

Dual functions of nitrogen and phosphorus co-doped carbon dots for drug-targeted delivery and two-photon cell imaging

Heteroatom-doping carbon dots (CDs) have excellent fluorescence properties. In the paper, nitrogen (N) and phosphorus (P) co-doped CDs (N, P-CDs) were prepared through the hydrothermal method and characterized by TEM, PXRD, FT-IR, 13C NMR, XPS, UV–vis, and fluorescence spectra. The optical properties and drug (doxorubicin) - delivery performance of N, P-CDs were also studied. The results showed that the average size of N, P-CDs was 3.64 nm and the quantum yield was 30 %. The N, P-CDs had down- and up-conversion fluorescence properties, and the luminescence mechanism of the N, P-CDs was explained. The drug loading capacity of N, P-CDs was 39.11 %, and the drug delivery system (N, P-CDs-DOX) had low cytotoxicity, sustained release, and pH-targeted properties. The in vitro release of N, P-CDs-DOX belonged to the Weibull model and Fick diffusion, exhibiting the same release model and mechanism with free DOX. The N, P-CDs could deliver DOX successfully, which was demonstrated by the co-collocation of N, P-CDs and DOX in SH-SY5Y cells through single/two-photon imaging. N, P-CDs could potentially be used in drug-targeted delivery and cell imaging.

Microwave-assisted method synthesis of Ag/CNQDs/g-C3N4 with excellent photocatalytic activity for the degradation of norfloxacin

In this paper, through microwave-assisted process combined with a chemical reduction method, the novel ternary photocatalysts Ag/CNQDs/g-C3N4 composites were prepared successfully for the norfloxacin removal. The Ag/CNQDs/g-C3N4 composites possessed the suitable specific surface area, better crystal structure and excellent stability. Furthermore, forming an internal electric field, the isotype heterojunction structure between CNQDs and g-C3N4 could promote effective carrier separation. Unexpectedly, the Ag/CNQDs/g-C3N4 with the synergistic effect of the up-conversion fluorescent properties of CNQDs and the surface plasmon resonance (SPR) effect of Ag NPs, showed the excellent photocatalytic property. As a result, the optimized Ag/CNQDs/g-C3N4 composites exhibit excellent photocatalytic degradation of norfloxacin under visible light irradiation. The norfloxacin removal rate was reached almost 100% within 120 min, and the quasi-first-order kinetic constant (k) value was 0.04233 min−1, which was more than 4 times higher than that of g-C3N4. Moreover, the·O2- and h+ were the dominant active species involved in the photo-degradation of norfloxacin. In the mineralization process, the toxicity of norfloxacin degradation intermediates gradually reduced. This work not only provides new insights for the design of g-C3N4-based composites for photocatalysis applications, but also affords an effective strategy in the environmental remediation field.

Dual-mode up/down-conversion optical thermometry of Pr<sup>3+</sup>-regulated Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup> phosphors

Photothermal sensing is crucial in developing smart wearable devices. However, designing and synthesizing luminescent materials with suitable multi-wavelength emission and constructing multiple sets of probes in a single material system is a huge challenge for constructing sensitive temperature sensors with a wide temperature range. In this paper, Pr<sup>3+</sup>, Er<sup>3+</sup> single-doped and double-doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors are successfully prepared by high temperature solid phase method, and their structures, morphologies, excitation wavelengths and temperature-dependent fluorescence properties are characterized by XRD, SEM, fluorescence spectrometer and self-made heating device. Firstly, the photoluminescences of the synthesized series of samples are investigated. The results show that comparing with the single-doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>: Er<sup>3+</sup> sample, the up/down-conversion spectra of Pr<sup>3+</sup>, Er<sup>3+</sup> co-doped phosphors under 808 nm/380 nm excitation show that the green fluorescence emission of Er<sup>3+</sup> is enhanced. In addition, under 980 nm excitation, Pr<sup>3+</sup> can effectively regulate the fluorescence energy level population pathway, so that the electrons are more effectively arranged in the <sup>2</sup>H<sub>11/2</sub> and <sup>4</sup>S<sub>3/2</sub> energy levels in the excitation process. The red emission is weakened and the green emission is enhanced, which improves the signal resolution of the fluorescent material and has a significant influence on the optical temperature measurement. Secondly, the up-conversion fluorescence property of Er<sup>3+</sup> under 808 nm/980 nm laser excitation in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup> and Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Pr<sup>3+</sup>,Er<sup>3+</sup> phosphors are investigated. The results show that the red and green fluorescence emissions of Er<sup>3+</sup> are two-photon processes. Finally, the up/down-conversion dual-mode temperature sensing properties of Er<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup> and Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Pr<sup>3+</sup>, Er<sup>3+</sup> phosphors are investigated. It is found that both materials have good optical temperature measurement performances. The Pr<sup>3+</sup> doping optimizes the dual-mode optical temperature measurement performances of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup> phosphors derived from the thermal coupling energy level of Er<sup>3+</sup> ions. In addition, the up/down-conversion fluorescence mechanism of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup> and Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub>:Er<sup>3+</sup>, Pr<sup>3+</sup> phosphors are proposed, and the enhanced green fluorescence by Pr<sup>3+</sup> co-doping is attributed to the energy transfer from Pr<sup>3+</sup> ions to Er<sup>3+</sup> ions, leading to the increase of green fluorescence level population and the decrease of red fluorescence level population of the Er<sup>3+</sup> ions. This new dual-mode optical temperature measurement material provides a material basis and optical temperature measurement technology for exploring other temperature measurement materials.

Facile Synthesis of NaYF4:Yb Up-Conversion Nanoparticles Modified with Photosensitizer and Targeting Antibody for In Vitro Photodynamic Therapy of Hepatocellular Carcinoma.

Rare Earth up-conversion nanoparticles NaYF4:20%Yb,2%Er@PEI (UCNPs) were generated via a one-step hydrothermal technique at relatively reduced temperatures. Photosensitizer Ce6 and anti-EpCAM, a highly expressed monoclonal antibody in cancer stem cells of hepatocellular carcinoma, were linked to UCNP surfaces via the formation of amide linkage between carboxyl from Ce6 or anti-EpCAM and abundant amino from PEI, leading to the formation of Ps-Ce6 and anti-EpCAM-UCNPs-Ce6 nanoparticles. The synthesized nanoparticles characterized by XRD, TEM, and IR, and their zeta potential, ROS generation ability, Ce6 loading rate, and up-conversion fluorescence properties were investigated. It has been revealed that all the products were uniformly dispersed nanoparticles (25–32 nm), which crystallized primarily as hexagonal structures, and their up-conversion fluorescence spectra were similar to that of NaYF4:20%Yb,2%Er. The Ce6 loading rate in the anti-EpCAM-UCNPs-Ce6 nanoparticles was about 2.9%, thereby resulting in good ROS generation ability. For anti-EpCAM-UCNPs-Ce6, the biosafety, targeting effect, and PDT effect exposed under near-infrared (NIR) laser (980 nm) were evaluated using human liver cancer cells (BEL-7404). The results showed that it has good biocompatibility and biosafety as well as high targeting and PDT treatment efficiencies, which renders it a potential experimental material for the near-infrared PDT study.

Room-temperature facile synthesis of hexagonal NaYF4 and NaYF4: Yb, Er powder without any organic additives and its upconversion fluorescence properties

Based on the structure difference between cubic and hexagonal phases, a facile method was designed for the synthesis of pure hexagonal phase β-NaYF4 and β-NaYF4: Yb, Er powder at room temperature and ambient pressure. In the whole process, neither any organic additives, nor high temperature and high pressure were involved that indicated an environmentally friendly technology. The optimal synthesis conditions for hexagonal phase at room temperature is the pH value between 5.0 and 6.5, the amorphous Y (OH) 3 as Y precursor and the F−/Y3+ molar ratio equal to 6:1. A possible preparation mechanism based on the difference between the coordination structure of the hexagonal and the cubic phases was also proposed. It is found that the as prepared powder of the hexagonal phase can emit red upconversion luminescence with a high R/G ratio, which is significantly different from the light emitted by the usually synthesized hexagonal phase. This method can also provide a new perspective for studying the sustainable synthesis of rare earth compounds.

Observation of up-conversion fluorescence from exciplex of m-MTDATA:TPBi blend

Exciplex-type thermally activated delayed fluorescence (TADF) materials exhibit charming application potential in organic light-emitting diodes. However, investigations on their non-linear optical properties are rather rare. Here, we report up-conversion fluorescence from an electron donor-acceptor exciplex blend composed of the donor 4,4′,4″-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine (m-MTDATA) and the acceptor 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi). Strong up-conversion fluorescence has been observed and a two-photon absorption (TPA) cross-section σ of ∼387 GM has been measured. The optical spectra analysis indicates that the TPA is dominated by the exciton absorption of m-MTDATA molecules. The observed up-conversion fluorescence is explained by a joint mechanism including TPA, exciplex formation, reverse intersystem crossing, and prompt or delayed fluorescence. The TADF and up-conversion fluorescence properties of this exciplex blend have great application potentials in linear and non-linear optics.

Synthesis and upconversion luminescence of α-Ba2ScAlO5 hosted compounds

α-Ba2ScAlO5 is considered the high-temperature counterpart of the room temperature β-Ba2ScAlO5 phase, which undergoes a phase transition at around 1700 ​°C. This study demonstrates that α-Ba2ScAlO5 can be synthesized using a traditional high-temperature solid-state approach that is highly stable at room temperature. The single-phase α-Ba2ScAlO5 was successfully obtained by adding excessive BaO and varying the ratio of Sc/Al in barium scandium aluminate. Furthermore, the up-conversion luminescence properties of the rare earth metals doped α-Ba2ScAlO5 was also investigated. The co-doped α-Ba2ScAlO5 with Yb3+ and Er3+ maintained a single-phase structure. The material exhibits good up-conversion fluorescence properties and emits a strong red light at 667 ​nm when excited by a 980 ​nm laser, which indicates a broad application prospect in the field of biomedical science.

The pH responsive upconversion fluorescence and photothermal conversion properties of NaYF4:Yb3+/Er3+@NaYF4@MnO2@Au.

While photothermal therapy is widely applied in phototherapy, there are still challenges in developing new generation phototherapy materials with precise diagnostic functions. Here we report the construction of a pH responsive upconversion fluorescence imaging precisely guided photothermal therapy system, namely NaYF4:Yb3+/Er3+@NaYF4@MnO2@Au nanocomposites, which can effectively avoid light damage to non-target tissues. Owing to the fluorescence resonance energy transfer between the upconversion nanocrystal donor and MnO2 and Au acceptor, the upconversion fluorescence is completely quenched. However, in pH 5.3 PBS buffer, MnO2 is gradually broken down, and the upconversion fluorescence is partially recovered, which could be used for upconversion fluorescence imaging to precisely guide photothermal therapy under 980 nm excitation. Simultaneously, due to the absorption of 980 nm excitation light and the emission bands of Er3+ (2H11/2→4I15/2 and 4S3/2→4I15/2 transition), temperature increment of core@shell@MnO2@Au could reach 35.5 °C under 980 nm excitation at 0.8 W cm-2. The core@shell@MnO2@Au nanocomposites are supposed to contribute significantly in the biological applications of photoluminescence imaging and photothermal therapy.

Facile Synthesis of Fluorescence/Temperature Multisensitive Hybrid Hydrogels

Hybrid hydrogels based on poly(N-isopropylacrylamide) and poly(acrylamide) containing CdTe quantum dots with UV sensitive response and including NaYF4:Yb/Er nanoparticles have been prepared through glow discharge electrolysis plasma. The fluorescence characteristic and temperature sensitivity of the prepared hydrogels have been most extensively studied. In addition, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry were determined to characterize the morphology, degree of crystallinity and the phase transformations of the hydrogels. The results suggested that the phase transition temperature of the hydrogels was 32.5°C and the hydrogels had good up-conversion and down-conversion fluorescence properties. Moreover, hybrid hydrogels had a reversible temperature response performance.

Hexadecylpyridinium Chloride Mediated Hydrothermal Synthesis of NaYF₄:Yb, Er Nanocrystal and Their Luminescent Properties.

Upconversion nanocrystals with uniform size and hydrophilic surface have potential applications in biological medical engineering. In this study, hydrophilic NaYF₄:Yb, Er nanospheres were synthesized via hexadecylpyridinium chloride (CPC) mediated hydrothermal process. The synthesized NaYF₄:Yb, Er upconversion nanospheres (UCNSs) were characterized by various characterization methods. Results showed that the synthesized UCNSs exhibited a uniform sphere-like structure with average diameter of ~250 nm. The surface of UCNSs was captured by CPC molecule indicating hydrophilic properties of UCNSs. The spherical UCNSs composed of mixed phase (α+β) NaYF₄ nanocrystals. This is the novel study for synthesis of NaYF₄:Ln3+ crystal employing CPC as ligand. Moreover, the effect of CPC concentration on synthesis of UCNSs was investigated by comparatively studying morphology, crystal phase and luminescent properties of desired sample prepared under different experimental conditions. It was found that high concentrations of CPC ligands were more favorable for forming NaYF₄ crystal nanospheres with morphology that is more regular, have smoother surface, with higher crystallinity and better upconversion fluorescent properties. The possible growing mechanism was proposed and growing of NaYF₄:Yb, Er nanospheres followed the classical Ostwald ripening process.

Ligand-free upconversion nanoparticles for cell labeling and their effects on stem cell differentiation

Recently, the wide application of upconversion nanoparticles (UCNPs) in the field of bioimaging has raised the requirement of biocompatibility. Current cytocompatibility studies on UCNPs mainly focus on cancer cells; however, their potential effects on normal cells are rarely addressed. Herein, the cellular effects of a trace amount of ligand-free NaYF4:Yb/Er nanocrystals on the differentiation of rat bone mesenchymal stem cells (rBMSCs) were investigated. First, due to their excellent upconversion fluorescent properties, the cellular uptake of ligand-free NaYF4:Yb/Er nanocrystals was confirmed by confocal laser scanning microscopy, and a homogeneous cytoplasmic distribution was imaged. Second, the viability of the rBMSCs cultured with a series of concentrations of nanoparticles (0, 30, 300, and 3000 ng ml−1) was evaluated, and a dose threshold was determined. Third, the effects of ligand-free NaYF4:Yb/Er nanocrystals on the osteogenesis of the rBMSCs were intensively characterized. The alkaline phosphatase activity assay, quantitative real time polymerase chain reaction for related osteogenic genes, and immunofluorescence staining of specific biomarkers and mineral deposits demonstrated that the ligand-free NaYF4:Yb/Er nanocrystals at a proper concentration can enhance osteogenic differentiation. Finally, intracytoplasmic lipid detection showed that the adipogenic differentiation of rBMSCs might be inhibited in the presence of ligand-free NaYF4:Yb/Er nanocrystals. Meanwhile, these results showed that the effects of ligand-free NaYF4:Yb/Er nanocrystals on rBMSCs were concentration-dependent and reciprocal between osteogenic and adipogenic differentiation. This work provides new insights into the exploring the biocompatibility of UCNPs and will benefit the research community engaged in nanotechnology and biomedicine.

Hot injection synthesis of core-shell upconversion nanoparticles for bioimaging application

In recent years, lanthanide-containing upconversion nanoparticles (UCNPs) have aroused the extensive interest in bioimaging due to their unique upconversion fluorescent properties, such as the high tissue penetration depth, good biocompatibility, low auto-fluorescence, and high imaging sensitivity. In this work, we synthesize a series of NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub> core-shell structured nanoparticles with various shell thicknesses. A “hot injection” strategy is introduced to fabricate the core-shell UCNPs through using high boiling-point mixtures (sodium/rare-earth trifluoroacetates dissolved in oleic acid and octadecene at 150 °C) as shell precursor solutions. The as-synthesized UCNPs are characterized by transmission electron microscope, particle size analysis and fluorescence spectra. The experimental results show that the shell thickness of UCNPs can be well controlled within a range from 4.2 nm to 32.6 nm by simply tuning the added quantity of the shell precursors. Meanwhile, the upconversion luminescence intensity of NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub> shows tens times higher than that of NaYF<sub>4</sub>:Yb, Tm owing to the effective suppression of surface quenching. The optimized thickness of the shell is determined to be 22.7 nm. An ultrathick inert shell (>22.7 nm) is not beneficial to upconversion luminescence mainly due to a strong scattering effect. In addition, the in vitro upconversion luminescent bioimaging application is demonstrated by using the as-synthesized core-shell structured UCNPs. Typically, the prepared OA capped UCNPs are dispersed in HCl solution to obtain hydrophilic ones, followed by polyethylene glycol (PEG) modification to improve their biological compatibility. The hydrophilic NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub>@PEG nanostructures (denoted as UCNP@PEG) show a good biocompatibility with HeLa cells, as the viability of HeLa cells do not decrease obviously when the concentration of UCNP@PEG increases to 0.2 mg/mL. Then, we evaluate the upconversion luminescent signals of UCNP@PEG in HeLa cells under the excitation of 980 nm laser. An obviously increasing upconversion luminescent signal can be observed in HeLa cells with the incubation time increasing from 0.5 h to 6.0 h, indicating that the UCNP@PEG can be used as an excellent luminescence probe for cell imaging and monitoring the cell endocytosis process. All in all, we offer an efficient “hot injection” strategy of fabricating the core-shell structured UCNPs with various shell thickness for improving the upconversion efficiency of UCNPs, which will pave the way for new bioimaging and medical applications.

Upconversion fluorescence property of Er3+/Yb3+ codoped lanthanum titanate microcrystals for optical thermometry

Optical thermometry technology plays a significant role in plenty of fields owing to its unrivaled properties such as sensitive, noncontact, reliable and so on. In this work, Er3+/Yb3+ codoped lanthanum titanate (La2Ti2O7) microcrystals have been synthesized by solid state reaction for optical thermometry. This novel prepared material for thermometry is based on the fluorescence intensity ratio of thermally coupled levels from upconversion emission under 980 nm excitation. The sensitivity of thermometry is 5.7 × 10−3 K−1, and the input power density is only 8.3 mW/mm2. Furthermore, the result of repeatability test illustrates that the as-prepared microcrystals possess excellent stability at the temperature range from 333 to 553 K. Therefore, these demonstrated advantages of Er3+/Yb3+ codoped La2Ti2O7 microcrystals make it a promising material in optical thermometry area.

Z-scheme CdS/CQDs/g-C3N4 composites with visible-near-infrared light response for efficient photocatalytic organic pollutant degradation

We have successfully synthesized novel Z-scheme CdS/CQDs/g-C3N4 composites with visible-near-infrared light response for the photocatalytic degradation of rhodamine B (RhB), methylene Blue (MB) and phenol. Based on the energy band matching theory, CdS was coupled with g-C3N4 using carbon quantum dots (CQDs) as the electron mediator to form the Z-scheme heterojunctions through a simple calcination process. Compared with the single-phase and binary composites, the Z-scheme CdS/CQDs/g-C3N4 composites not only exhibited enhanced photocatalytic activity and photostability but also realized near-infrared light response. CQDs, as the electron mediator, can shuttle the electrons in the CdS/CQDs/g-C3N4 interface via the Z-scheme electron transfer pathway, which lead to improvements in charge separation and oxidizability of the composites. The Z-scheme electron transfer was verified using various techniques, including PL, EIS, EPR and transient photocurrent response. The mechanism of Z-scheme charge transfer was also proposed for the improved photocatalytic RhB degradation activity. In addition, CQDs can capture near-infrared light through the upconversion fluorescence property, ameliorating the broad- spectrum photocatalytic competence. Therefore, the Z-scheme heterojunction with visible-near-infrared light response was utilized to improve charge separation, oxidizability and solar energy utilization, as well as to provide new insights for the construction of CQDs-based Z-scheme composites for photocatalysis applications.

A facile approach to synthesis carbon quantum dots-doped P25 visible-light driven photocatalyst with improved NO removal performance

The water-soluble carbon quantum dots (CQDs) and a novel composite photocatalyst CQDs/P25 have been prepared by a one-step electrochemical-microwave method. The experimental result shows that the photocatalytic degradation of NO by this new kind of CQDs/P25 composite reaches 71%, which is approximately 1.65 times than that of the pure P25 at room temperature. The initial concentration of NO pollutants is 10 ppm. The photocatalytic efficiency of the composite catalyst achieves the highest when the content of CQDs is 1%. It can be concluded that the CQDs extend the light absorption range and adjust the band gap of pure P25. The high photocatalytic performance of this new kind of photocatalyst can be mainly attributed to the unique up-conversion fluorescence property, nanometer size effect and surface activity effect.

Preparation of CQDs with hydroxyl function for Fe 3+ detection

Owing to its excellent fluorescence stability, unique up-conversion fluorescence properties and biocompatibility, carbon-quantum dots (CQDs) have become a research hot spot in the field of carbon materials. This study used a series of different preparation strategies to synthesise CQDs such as microwave method, solvothermal method and hydrothermal method. The prepared quantum dots can be further applied to design and metal ion detection. It is worth noting that the CQDs prepared by the hydrothermal method are evenly distributed in the range of 2-3 nm without any agglomeration. Fluorescence quenching was performed by Fe 3+ , and the introduction of PO 4 3- ion could increase the fluorescence intensity of CQDs-Fe 3+ system. Furthermore, CQDs were hydroxyl functionalised by treating with ethanol. The functionalised CQDs synthesised by solvothermal method greatly enhanced the fluorescence intensity.

Fabrication and up-conversion fluorescence property of Er3+/Yb3+co-doped Ca-Si-Ti biomaterials

This work demonstrates bulk-type up-conversion biomaterials which could be used as a bone repair material with the ability to monitor bone mineralization. Er3+/Yb3+ co-doped Ca-Si-Ti (CST3: TiO2 content is 30 mol%) bulk biomaterials were prepared via containerless processing technique in an aerodynamic levitation furnace and with subsequently heat treatment. The up-conversion fluorescence property was influenced by Yb3+ doping concentration, heat-treatment and mineralization in simulated body fluid (SBF). Optimum emission intensities were obtained for the sample with 20 mol% of Yb3+ doping concentration and heat treatment at 937 °C for 2 h. Hydroxyapatite (HAP) deposition was observed on the surface of the samples after soaking in SBF for 14 days, and the up-conversion fluorescence intensity of the samples decreased with the increase of soaking time. This indicates that Er3+/Yb3+ co-doped CST3 materials are bioactive, in which the HAP mineralization in bone repair could be monitored by measuring the intensity change of up-conversion fluorescence.