Yue Zhai

Facilely prepared carbon dots and rare earth ion doped hybrid composites for ratio-metric pH sensing and white-light emission

A facile method was developed to synthesize fluorescent carbon-dot–Eu3+ hybrid composites (CD–Eu–HCs) by one-pot hydrothermal methods. The prepared composites demonstrate unique dual fluorescence which originates from the blue emission of the CDs and intrinsic photoluminescence of the Eu3+ ions, respectively. Moreover, such dual fluorescent characteristics show quite different responses for different pH value environments and have been developed in a ratiometric pH sensor. Lastly, they can realize white light emission by co-doping of Tb3+ and the color temperature becomes tunable by adjusting the relative proportion of Eu3+.

Carbon dots with efficient solid-state photoluminescence towards white light-emitting diodes

Carbon dots (CDs) exhibit excellent ultraviolet (UV) absorption and tunable photoluminescence over the full visible light range, which endows CDs with huge potential to be designed as efficient full-color emitting phosphors for UV to white light conversion. However, the low quantum yield (QY) for white light emission and solid-state quenching dramatically limit their optoelectronic applications. We proposed an effective strategy for modulating the emitting states of colloidal CDs by introducing hexadecyltrimethyl ammonium bromide. Consequently, white light emission with tunable correlated color temperature from 8121 K to 3623 K was realized. Furthermore, we dispersed CDs in a PVP matrix for solid-state films, where the solid-state quenching was effectively avoided. A white light-emitting QY of 38.7% was thus achieved through the inhibition of non-radiative electron–hole recombination as well as the cooperation between the intrinsic state of the carbogenic cores and the surface-related state of the organic ligands. The white light emitting QY is much higher than that of other reported CDs (ca. 15% in the soluble state and not reported in the solid-state) and is comparable to that of the nanophosphors with the highest UV pumped single-component white light emissions reported in the literature.

Carbon dot/polyvinylpyrrolidone hybrid nanofibers with efficient solid-state photoluminescence constructed using an electrospinning technique

Carbon dots (CDs) are the promising candidates for application in optoelectronic and biological areas due to their excellent photostability, unique photoluminescence, good biocompatibility, low toxicity and chemical inertness. However, the self-quenching of photoluminescence as they are dried into the solid state dramatically limits their further application. Therefore, realizing efficient photoluminescence and large-scale production of CDs in the solid state is an urgent challenge. Herein, solid-state hybrid nanofibers based on CDs and polyvinylpyrrolidone (PVP) are constructed through an electrospinning process. The resulting solid-state hybrid PVP/CD nanofibers present much enhanced photoluminescence performance compared to the corresponding pristine colloidal CDs due to the decrease in non-radiative recombination of electron-holes. Owing to the suppressed self-quenching of CDs, the photoluminescence quantum yield is considerably improved from 42.9% of pristine CDs to 83.5% of nanofibers under the excitation wavelength of 360 nm. This has great application potential in optical or optoelectronic devices.

Green fluorescent organic nanoparticles based on carbon dots and self-polymerized dopamine for cell imaging

Fluorescent organic nanoparticles (FONs) based on polydopamine (PDA) have recently emerged as a novel fluorescent probe due to its facile synthesis procedure, good water solubility, and excellent biocompatibility. However, previously reported PDA-FONs show low monodispersity and efficiency, which largely limit their application. In this study, we report a new type of FONs that has been prepared using carbon dots (CDs) as seeds and assembled via the self-polymerization of dopamine molecules. The prepared FONs showed high efficiency and monodispersity; moreover, via controlling the time of the polymerization reaction, different FONs could be obtained, which demonstrated similar structures but with tunable emission properties, and the emission gradually evolved from blue to green with the increasing reaction time. The mechanism of the prepared FONs was confirmed to be via the Forster resonance energy transfer (FRET) effect occuring between CDs and polymerized dopamine, leading to high efficiency and tunable emission. The FONs were also explored for cell imaging and cytotoxicity experiments, and they showed excellent biocompatibility and good prospects in biotechnological applications.

Modulation of the photoluminescence in carbon dots through surface modification: from mechanism to white light-emitting diodes

Carbon dots (CDs) have emerged as a new type of fluorescent material because of their unique optical advantages, such as high photoluminescence quantum yields (QYs), excellent photo-stability, excitation-dependent emissions, and low toxicity. However, the photoluminescence mechanism for CDs remains unclear, which limits their further practical application. Here, CDs were synthesized via a solvothermal route from citric acid and urea. Through the oxidation and reduction treatment of pristine CDs, the origin of the photoluminescence and the involved mechanism were revealed. We found that the blue/green/red emissions originated from three diverse emitting states, i.e. the intrinsic state, and C=O- and C=N-related surface states, respectively. Based on the as-prepared CDs, a pH sensor depending on the radiometric luminescence detection was developed. Furthermore, we constructed CD/PVP (PVP, polyvinylpyrrolidone) composite films, which exhibited white light emission with photoluminescence QYs of 15.3%. The white light emission with different correlated color temperatures (CCTs), from 4807 K to 3319 K, was obtained by simply changing the amount of PVP solution. Benefiting from the white light-emitting solid-state films, single-component white light-emitting diodes were fabricated with an average color rendering index value (Ra) of 80.0, luminous efficiency of 10.2 lm W-1, and good working stability, thus indicating a promising potential for practical lighting applications.

Luminescence carbon dot-based nanofibers for a water-insoluble drug release system and their monitoring of drug release

Drug release systems with fluorescence detection have emerged as a potential application for the biological area of diagnosis and therapy. Carbon dots (CDs) are a promising fluorescence probe for application in a drug release system due to their excellent biocompatibility, low toxicity, chemical inertness, and non-blinking fluorescence emission. Herein, we developed a composite nanocarrier based on fluorescent CDs and polyvinylpyrrolidone (PVP) through an electrospinning technology. The as-prepared PVP/CD-ketoprofen (PVP/CD-KET) composite nanofiber presents bright blue-light fluorescence with a photoluminescence quantum yield (QY) of 65.7% and was utilized for loading a water-insoluble drug and moreover for monitoring the drug release process. In vitro tests indicate that the photoluminescence emission intensity of the CDs and the cumulative amount of KET released from the PVP/CD-KET composite nanofiber gradually increase with the release time. Furthermore, the emission intensity of the CDs as a function of the cumulative released amount of KET can be summarized by a power function. The correlation between the emission intensity of CDs and drug release amount can be potentially used to monitor the drug release process.

Impurity Ions Codoped Cesium Lead Halide Perovskite Nanocrystals with Bright White Light Emission towards UV-WLED

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have attracted extensive interests. However, the native ion exchange among halides makes them extremely difficult to realize the white emission. Herein, we demonstrate a novel strategy to obtain WLED phosphors based on the codoping of different metal ion pairs, such as Ce3+/Mn2+, Ce3+/Eu3+, Ce3+/Sm3+, Bi3+/Eu3+, and Bi3+/Sm3+ into stable CsPbCl3 and CsPbCl xBr3- x NCs. Notably, by the typical anion exchange reaction, the highly efficient white emission of Ce3+/Mn2+-codoped all-inorganic CsPbCl1.8Br1.2 perovskite NCs was achieved, with an optimal photoluminescence quantum yield of 75%, which is much higher than the present record of 49% for single perovskite phosphors. Moreover, the WLED with a luminous efficiency of 51 lm/W based on the 365 nm ultraviolet chip and CsPbCl1.8Br1.2:Ce3+/Mn2+ nanophosphor was achieved. This work represents a novel device for perovskite-based phosphor-converted WLEDs.