Shaobo Cui

Local Field Modulation Induced Three‐Order Upconversion Enhancement: Combining Surface Plasmon Effect and Photonic Crystal Effect

A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) (PMMA) opal photonic crystals. On the surface of the SPPC, the overall upconversion luminescence intensity of NaYF4 :Yb(3+) , Er(3+) under 980 nm excitation is improved more than 10(3) fold. The device is easily shifted to a transparent flexible substrate, applied to flexible displays.

Ag-SiO2-Er2O3 Nanocomposites: Highly Effective Upconversion Luminescence at High Power Excitation and High Temperature

Rare Earth (RE) activated upconversion phosphors (UCPs), have demonstrated significant application potentials in some front fields, including solar energy conversion and bio-application. However, some bottleneck problems should be overcame, such as the lower upconversion efficiency, narrower excitation band, concentration-quenching and temperature-quenching. To solve these problems, the Ag-SiO2-Er2O3 nanocomposites were fabricated, in which the upconversion luminescence (UCL) of Er2O3 was white broadband. Through the interaction of Er2O3 with surface plasmon (SP) of silver nanoparticles (SNPs), the threshold power for generating broadbands was suppressed largely in contrast to the Er2O3 nanoparticles (NPs), while the UCL brightness was enhanced remarkably, ranging from several to 104 times, which strongly depended on the power density of excitation light. At excitation power density of 1.50 W/mm2 of 980 nm light, the UCL intensity of Ag-SiO2-Er2O3 is 40-folds than the well-known NaYF4:Yb3+,Er3+ commercial powders. And more, it is also interesting to observe that the composites demonstrate two excitation bands extending of 780–980 nm, highly improved UCL with elevated temperature and excitation power density. The UCL mechanism related to UCL enhancement was carefully studied.

Nd2O3/Au nanocomposites: upconversion broadband emission and enhancement under near-infrared light excitation

In the present work, a novel strategy for the synthesis of Nd2O3/Au nanocomposites was successfully applied by a co-precipitation process, in which the upconversion luminescence (UCL) of Nd2O3 was a white broadband emission under 780–980 nm excitation. UCL enhancement in Nd2O3/Au nanocomposites with different doped concentrations of Au nanorods (NRs) under 980 nm and 808 nm excitation was systemically studied. It was observed that by the interaction of Nd2O3 with surface plasmon (SP) of Au NRs, the threshold power for generating broadbands was largely suppressed in contrast to the Nd2O3 nanoparticles (NPs). Further, it was interesting to observe that the enhancement was strongly dependent on the doped concentration of Au NRs and the excitation power of 980 nm and 808 nm laser diodes. The optimum UCL enhancement was 11-fold and 9-fold at 980 nm and 808 nm excitation, respectively. In addition, the upconversion (UC) broadband emission and UCL enhancement mechanism of Nd2O3/Au nanocomposites were proposed.

Paper-based upconversion fluorescence resonance energy transfer biosensor for sensitive detection of multiple cancer biomarkers.

A paper-based upconversion fluorescence resonance energy transfer assay device is proposed for sensitive detection of CEA. The device is fabricated on a normal filter paper with simple nano-printing method. Upconversion nanoparticles tagged with specific antibodies are printed to the test zones on the test paper, followed by the introduction of assay antigen. Upconversion fluorescence measurements are directly conducted on the test zones after the antigen-to-antibody reactions. Furthermore, a multi-channel test paper for simultaneous detection of multiple cancer biomarkers was established by the same method and obtained positive results. The device showed high anti-interfere, stability, reproducible and low detection limit (0.89 ng/mL), moreover it is very easy to fabricate and operate, which is a promising prospect for a clinical point-of-care test.

Uniform Eu3+-doped YF3 microcrystals: inorganic salt-controlled synthesis and their luminescent properties

A variety of microstructured YF3:Eu3+ with different morphologies have been successfully synthesized using a simple inorganic salt as the only structure-directing agent in the hydrothermal system. The cations of Al3+, Li+, Mg2+, Na+, K+ and Ba2+ were found to determine the size and morphology of the as-prepared microstructured YF3. The prepared samples were systematically characterized by powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) and photoluminescent excitation spectra (PLE). Detailed proofs indicated that the process of growing different morphologies of YF3:Eu3+ microparticles were dominated by different growth mechanisms. Furthermore, photoluminescent properties were also investigated.

Highly modified spontaneous emission in NaY(MoO4)2:Yb3+/Er3+ inverse opal photonic crystals

The up-conversion luminescence (UCL) of rare earth (RE) ion doped nanomaterials has attracted extensive interest because of its wide and great potential application. However, the lower UCL efficiency due to the local thermal effect among the ions is still an obstacle for real application. Photonic modulation is a novel way to suppress the local thermal effect and cross relaxation. In this work, NaY(MoO4)2:Yb3+/Er3+ inverse opal photonic crystals (IOPCs) were fabricated through the poly methylmethacrylate (PMMA) template and the modification of the IOPC structure on the emission spectra and dynamic of Er3+ ions was systemically studied. It is interesting to observe that in the IOPCs, the high-order UCL 2H9/2 → 4I15/2 was relatively enhanced. At the same time, the local thermal effect induced by laser irradiation was suppressed. The studies on UCL dynamics indicated that the nonradiative transition rate of Er3+ was considerably suppressed. The facts above indicated that in the IOPCs, the UCL efficiency of Er3+ was improved due to the periodic macroporous structure.

Highly sensitive and selective detection of mercury ions based on up-conversion FRET from NaYF4:Yb3+/Er3+ nanophosphors to CdTe quantum dots

The detection of Hg2+ has attracted considerable attention because of the serious health and environmental problems caused by it. There has been progress in the development of fluorescence biosensors based on quantum dots (QDs) for the detection of Hg2+. However, most of them are valid only in aqueous solution rather than in human serum due to the influence of protein autofluorescence in serum excited by ultraviolet or visible light. Herein, we designed and synthesized a novel NaYF4:Yb3+, Er3+ upconversion nanoparticle (UCNP)/CdTe QD composite probe for Hg2+ detection. The NaYF4:Yb3+, Er3+ UCNPs were synthesized via a solvothermal method. By grafting the CdTe QD probe onto the surface of the NaYF4:Yb3+, Er3+ UCNP, a fluorescence resonance energy transfer (FRET) biosensor for determination of Hg2+ ions was obtained under the pumping of 980 nm infrared light, which was capable of overcoming autoluminescence from serum. The spectral response towards Hg2+ suggested that the fluorescence intensity of the QDs reduced linearly with increasing Hg2+ concentration. The sensor showed high selectivity, a low detection limit of 15 nM and good linear Stern–Volmer characteristics, both in the buffer and serum. This biosensor has great potential for real applications of Hg2+ detection in biological and analytical fields.

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.

Observation of upconversion white light and ultrabroad infrared emission in YbAG:Ln3+ (Ln = Nd, Sm, Tb, Er)

We report on the intense white-light upconversion and ultrabroad infrared (IR) emission for the sol–gel synthesis of Yb3Al5O12 (YbAG):Ln3+ (Ln = Nd, Sm, Tb, Er) following excitation with low-energy near-infrared light (λex = 980 nm). Sufficient cross relaxations and photon avalanches play important roles in the formation of efficient visible and IR broad bands. The brightness of white-light upconversion was 6.2 × 104 cd/m2 at a laser power of 1.47 W, and the IR broad bands (1200–1700 nm) covered all the bands in optical communication media, which indicates that the material might be promising for the development of devices such as white lasers, LEDs, and integrated waveguides.

Plasmonic enhancement of the upconversion fluorescence in YVO4:Yb3+, Er3+ nanocrystals based on the porous Ag film

The upconversion luminescence (UCL) enhancement based on the surface plasmonic resonance (SPR) of noble metals is a promising way to improve UCL efficiency. However, it is still a challenge to achieve stable and effective UCL enhancement. Here, we present the preparation of the porous Ag/YVO4:Yb(3+), Er(3+) composite film via a simple double annealing method. It is exciting to observe that a maximum 36-fold ((2)H11/2-(4)I15/2) and 30-fold ((4)S3/2-(4)I15/2) UCL enhancement in the porous Ag/YVO4:Yb(3+), Er(3+) composite film, attributed to the effective coupling between SPR and the excitation light by adjusting the SPR peak to the excitation wavelength, controlling the effective coupling distance and improving the scattering-absorption ratio. Furthermore, the enhancement factor strongly depended on the excitation power and the Er(3+) concentration.