Jinyang Zhu

Doping Lanthanide into Perovskite Nanocrystals: Highly Improved and Expanded Optical Properties

Cesium lead halide (CsPbX3) perovskite nanocrystals (NCs) have demonstrated extremely excellent optical properties and great application potentials in various optoelectronic devices. However, because of the anion exchange, it is difficult to achieve white-light and multicolor emission for practical applications. Herein, we present the successful doping of various lanthanide ions (Ce3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+, and Yb3+) into the lattices of CsPbCl3 perovskite NCs through a modified hot-injection method. For the lanthanide ions doped perovskite NCs, high photoluminescence quantum yield (QY) and stable and widely tunable multicolor emissions spanning from visible to near-infrared (NIR) regions are successfully obtained. This work indicates that the doped perovskite NCs will inherit most of the unique optical properties of lanthanide ions and deliver them to the perovskite NC host, thus endowing the family of perovskite materials with excellent optical, electric, or magnetic properties.

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+.

Fabrication of Au-Ag nanocage@NaYF4@NaYF4:Yb,Er core-shell hybrid and its tunable upconversion enhancement

Localized electric filed enhancement by surface plasmon resonance (SPR) of noble metal nanoparticles is an effective method to amplify the upconversion luminescence (UCL) strength of upconversion nanoparticles (UCNPs), whereas the highly effective UCL enhancement of UCNPs in colloids has not been realized until now. Here, we designed and fabricated the colloidal Au-Ag nanocage@NaYF4@NaYF4:Yb,Er core-shell hybrid with different intermediate thickness (NaYF4) and tunable SPR peaks from visible wavelength region to NIR region. After the optimization of the intermediate spacer thickness (~7.5 nm) of NaYF4 NPs and the SPR peak (~950 nm) of noble metal nanoparticles, an optimum enhancement as high as ~25 folds was obtained. Systematic investigation indicates that UCL enhancement mainly originates from the influence of the intermediate spacer and the coupling of Au-Ag nanocages with the excitation electromagnetic field of the UCNPs. Our findings may provide a new thinking on designing highly effective metal@UCNPs core-shell hybrid in colloids.

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.

Size-dependent downconversion near-infrared emission of NaYF4:Yb3+,Er3+ nanoparticles

Near-infrared-downconversion-near-infrared (NIR-DC-NIR) bioimaging based on lanthanide doped upconversion nanoparticles (UCNPs) has received much attention due to its deeper penetration, and higher contrast imaging and signal-to-noise ratio in biological tissues. The size of UCNPs determines the mechanism and rate of cell uptake of the nanoparticles and their ability to permeate through biological tissues. Herein, we experimentally and theoretically demonstrate downconversion-near-infrared (DC-NIR) emission behavior in different sized UCNPs ranging from 5–150 nm. Interestingly, 15–40 nm UCNPs have more effective DC-NIR emissions than 150 nm UCNPs and an extremely high excitation threshold, which is entirely different from the size-dependent upconversion-visible (UC-VIS) emissions usually observed in UCNPs. We also observed that the intensity ratio of the DC-NIR emission to the UC-VIS emission decreases with the increase of the particle size and the excitation power, attributed to the more efficient upconversion (UC) process. Finally, we further confirmed that the competition process between the UC population and non-radiative relaxation to the DC-NIR level plays a key role in size-independent DC-NIR emissions. Our discovery would provide guidance for optimizing and designing NIR-DC-NIR NPs for bioimaging applications.

Remarkable Enhancement of Upconversion Luminescence on Cap-Ag/PMMA Ordered Platform and Trademark Anticounterfeiting

High brightness of upconversion luminescence (UCL) for a thinner layer of UC nanoparticles is significant for routine applications of effective trademark anticounterfeiting technology. In this work, efficient UCL of NaYF4:Yb3+,Er3+/Tm3+ was realized by combining a Ta2O5 dielectric layer on the cyclical island silver films supported by poly(methyl methacrylate) opal photonic crystals (PCs). The synergistic modulation of localized surface plasmon resonance and PC effect results in a significant improvement of the local electromagnetic field and an optimum UC enhancement of 145 folds. Furthermore, colorful pattern nanoprinting has been applied to this composite and used for trademark anticounterfeiting. The combination of angle-dependent PC effect and infrared-to-visible UCL represents a more advanced anticounterfeiting technique.

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.

Photoluminescence enhancement of carbon dots induced by hybrids of photonic crystals and gold–silver alloy nanoparticles

Carbon dots are attracting worldwide interest owing to their unique optical properties and great potential for application. However, orange/red emission carbon dots are still rare and exhibit relatively low efficiency. In this work, we present a novel strategy to enhance the fluorescence intensity of orange carbon dots, by synergistically manipulating an electromagnetic field through opal photonic crystals and the localized surface plasmon resonance of a metal structure. An optimum intensity enhancement of 25-fold was obtained for a modulated sample of PMMA opal photonic crystals and 53-fold for PMMA opal photonic crystals/Au–Ag alloy plasmon hybrids. The local electromagnetic field distribution for the PMMA opal photonic crystals/Au–Ag hybrid is calculated by the finite difference time domain method. Furthermore, a fingerprint identification system based on synergistic modulation is realized in the composite system, which provides novel insights into the potential applications of carbon dot films.

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.