Pingwei Zhou

NaYF4:Yb,Tm nanocrystals and TiO2 inverse opal composite films: a novel device for upconversion enhancement and solid-based sensing of avidin.

Upconversion luminescence (UCL) detection based on rare-earth doped upconversion nanocrystals (UCNCs) as probes has been proved to exhibit a large anti-Stokes shift, no autofluorescence from biological samples, and no photobleaching. However, it is still a challenge to achieve a stable, reproducible solid-based UCL biosensor because of ineffective UCL of the UCNCs. In this work, we fabricated TiO2 inverse opal photonic crystals (IOPCs)/NaYF4:Yb(3+),Tm(3+) (Er(3+)) UCNC composite films, which can tremendously improve the overall UCL of Tm(3+) as high as 43-fold. Based on the fluorescence resonance energy transfer (FRET) and the specific interaction between biotin and avidin, a novel solid-based UC biosensor is presented for sensing avidin. This solid-based detection system is convenient for detection, and also can offer two parameters for detecting trace amounts of avidin, namely, the emission intensity and the fluorescence decay time. The sensor has a high sensitivity of 34 pmol(-1), a good linear relationship of 0.996 and a low detection limit of 48 pmol. It also exhibits excellent long-time photostability, and the absence of autofluorescence, and thus may have great potential for versatile applications in biodetection.

Observation of Considerable Upconversion Enhancement Induced by Cu2–xS Plasmon Nanoparticles

Localized surface plasmon resonances (LSPRs) are achieved in heavily doped semiconductor nanoparticles (NPs) with appreciable free carrier concentrations. In this paper, we present the photonic, electric, and photoelectric properties of plasmonic Cu2-xS NPs/films and the utilization of LSPRs generated from semiconductor NPs as near-infrared antennas to enhance the upconversion luminescence (UCL) of NaYF4:Yb(3+),Er(3+) NPs. Our results suggest that the LSPRs in Cu2-xS NPs originate from ligand-confined carriers and that a heat treatment resulted in the decomposition of ligands and oxidation of Cu2-xS NPs; these effects led to a decrease of the Cu(2+)/Cu(+) ratio, which in turn resulted in the broadening, decrease in intensity, and red-shift of the LSPRs. In the presence of a MoO3 spacer, the UCL intensity of NaYF4:Yb(3+),Er(3+) NPs was substantially improved and exhibited extraordinary power-dependent behavior because of the energy band structure of the Cu2-xS semiconductor. These findings provide insights into the nature of LSPR in semiconductors and their interaction with nearby emitters and highlight the possible application of LSPR in photonic and photoelectric devices.

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.

NaYF4:Yb3+,Tm3+ inverse opal photonic crystals and NaYF4:Yb3+,Tm3+/TiO2 composites: synthesis, highly improved upconversion properties and NIR photoelectric response

A novel solvent-thermal Y2O3 template method was explored to synthesise NaYF4:Yb3+,Tm3+ inverse opal photonic crystals (IOPCs), which show highly improved up-conversion luminescence properties.

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.

Modulation of upconversion white light emission in PMMA/NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ composite photonic crystals

In recent years, spontaneous emission modulation of emitters in photonic crystals (PCs) has been widely reported. However, the modulation of PCs on upconversion (UC) white light emission has been rarely studied. In this Letter, triply doped PMMA/NaYF(4):Yb(3+), Er(3+), Tm(3+) composite photonic crystals were successfully fabricated and white light emission was obtained. It is interesting to observe that the chromaticity could be conveniently tuned by changing the photonic stop band (PSB), the incident angle, or the power of the excitation light.

Controllable chrominance and highly improved luminescent quantum yield of YV 1-x P x O 4 : Tm, Dy, Eu inverse opal white light phosphors

In this work, rare earth (RE) ions tri-doped YV(1-x)P(x)O(4): RE(3+) (RE = Tm, Dy, Eu) inverse opal photonic crystals (IOPCs) were fabricated by the PMMA template method, which demonstrated efficient white light emissions under ultraviolet excitation. It is significant to observe that the chrominance of the white light could be largely modulated by the photonic stop band of the IOPCs. And more, the photoluminescence quantum yield in the IOPCs was largely improved over the grinded reference (REF) because the undesired energy transfer (ET) process was effectively restrained.

ZnWO4/ZnWO4 : Eu3+ inverse opal photonic crystal scintillator: efficient phosphors in radiation detection

Phosphors with photonic crystal (PC) structures may demonstrate modulated optical properties and have potential applications in various optical devices. In this study, we represent the fabrication of ZnWO4 and ZnWO4 : Eu3+ inverse opal photonic crystal (IOPC) scintillators based on polymethyl methacrylate (PMMA) templates. Typical modified photoluminescent properties in PCs were observed such as the suppression of emissions near the edge of photonic stop bands (PSBs) and prolonged decay time constants. Moreover, it is very interesting to observe that the luminescent quantum efficiency of the IOPC samples was remarkably enhanced compared to the corresponding ground powder references (REFs) and the quantum efficiency of ZnWO4 IOPCs was as high as 70%, which was almost the optimum among various ZnWO4-based phosphors reported before. Furthermore, the energy transfer (ET) efficiency from tungstate groups to Eu3+ was determined based on luminescent dynamics, which indicated that the efficiency in the IOPCs was considerably improved compared to that in the REFs owing to the suppression of the spontaneous emission rate for the tungstate groups. It was also demonstrated that ZnWO4 : Eu3+ IOPCs could be used as white light phosphors.