Construction of active-inert core-shell structured nanocrystals for broad range multicolor upconversion luminescence.

Rare earth doped up-conversion luminescent nano-materials exhibit abundant emission colors under suitable excitation condition. In this work, NaYF4:Er/Ho@NaYF4 and NaYbF4:Tm@NaYF4 nanoparticles were synthesized by co-precipitation method. The pure red emission can be realized by the designed NaYF4:Er/Ho@NaYF4 nanocrystals and the R/Gs reach 23.3 and 25 under excitations of 980 and 1550 nm lasers, respectively. The R/G declines as the power increasing with the emission color changing from red to yellow, which is due to the quick saturation of the energy levels, radiating red emissions. Meanwhile, the emission intensity of NaYbF4:Tm@NaYF4 nanocrystals increases by 58.3 folds after encasing the inert shell NaYF4 and the CIE color coordinate reaches (0.1646, 0.0602) under 980 nm laser excitation. Furthermore, broad range multicolor from blue to red and yellow up-conversion emissions is achieved by mixing NaYF4:Er/Ho@NaYF4 and NaYbF4:Tm@NaYF4 nanocrystals, which could be applied to colorful displaying, security anti-counterfeiting and information coding.

Up-Conversion Luminescence and Temperature Sensing of Er3+/Yb3+ Codoped Y2(1-x %)Lu2x %O3 Solid Solution.

In this paper, Er3+/Yb3+ codoped Y2(1-x%)Lu2x %O3 solid solution was prepared through the sol-gel method, and the substitution of Y3+ by Lu3+ ions in Y2O3 was confirmed by X-ray diffraction data. The up-conversion emissions of samples under 980 nm excitation and the relative up-conversion processes are investigated. The emission shapes do not vary with the change in doping concentration due to the unaltered cubic phase. The red-to-green ratio changes from 2.7 to 7.8 and then declines to 4.4 as the doping concentration of Lu3+ increases from 0 to 100. The emission lifetimes of green and red have similar variation: the emission lifetime decreases with doping concentration changing from 0 to 60 and rises as the doping concentration continues to increase. The reason why the emission ratio and lifetime change could be originated to the exacerbation of cross-relaxing process and the change of radiative transition probabilities. The temperature-dependent fluorescence intensity ratio (FIR) shows that all samples can be used in noncontact optical temperature sensing, and the method of local structure distortion can be used to improve sensitivity further. The max sensing sensitivities of FIR based on R 538/563 and R red/green reach 0.011 K-1 (483 K) and 0.21 K-1 (300 K). The results display that Er3+/Yb3+ codoped Y2(1-x %)Lu2x %O3 solid solution can be potential candidates for optical temperature sensing in different temperature ranges.

Evolution of high-order Tamm plasmon modes with a metal-PhC cavity.

We put forward the concept of high-order Tamm plasmon (TP) modes which are illustrated with a simple metal-Bragg mirror cavity. Results show series orders of TP modes are gradually generated through adjusting the thickness of the cavity, for which traditional TP modes only corresponds to the zero-order modes. The reflectance spectra and electric field distributions are compared to demonstrate the consistency of these series of TP modes. Meanwhile, the excitation intensity of different order TP modes are studied. Results show that the excitation intensity is related directly to the TP mode wavelength, and has no relation to the order number. These results might provide new ideas to the study of TP modes and guide the design and optimization of TP based devices.

Real-Time Visual Sensing of Heat or Mass Transfer Processes for Microfluids via Tamm Plasmon Polaritons.

Heat or mass transfer processes of microfluids are very important in bioscience, environmental engineering, and food science, which are still hard to detect in real time. To overcome this difficulty, we try to use Tamm plasmon polaritons to enhance the interaction of light with microfluids. The main structure of the proposed configuration is Ag-photonic crystal (PhC) cavity, which can generate strong photonic localization by exciting Tamm plasmon polaritons. The results show that the enhancement of light intensity reaches ∼90 times in the cavity and the reflectance spectrum of the proposed structure exists in a narrow valley near 632.8 nm. This illustrates the generation of Tamm plasmon polaritons in the proposed structure. By injecting the microfluids into the cavity, the heat and mass transfer processes of the microfluids will have considerable influence on the reflectance of the proposed structure. Simulation results show that the concentration or temperature distributions of the microfluids can be effectively detected by analyzing the brightness of the imaging pictures, which is real-time and visible. Meanwhile, the sensitivity of the proposed configuration can be tuned by setting proper base parameters. This proposed configuration will have great potential in the study of microfluids, especially for the dynamic processes.

Up-Converting Luminescence and Temperature Sensing of Er3+/Tm3+/Yb3+ Co-Doped NaYF4 Phosphors Operating in Visible and the First Biological Window Range.

Accurate and reliable non-contact temperature sensors are imperative for industrial production and scientific research. Here, Er3+/Tm3+/Yb3+ co-doped NaYF4 phosphors were studied as an optical thermometry material. The typical hydrothermal method was used to synthesize hexagonal Er3+/Tm3+/Yb3+ co-doped NaYF4 phosphors and the morphology was approximately rod-like. The up-conversion emissions of the samples were located at 475, 520, 550, 650, 692 and 800 nm. Thermo-responsive emissions from the samples were monitored to evaluate the relative sensing sensitivity. The thermal coupled energy level- and non-thermal coupled energy level-based luminescence intensity ratio thermometry of the sample demonstrated that these two methods can be used to test temperature. Two green emissions (520 and 550 nm), radiated from 2H11/2/4S3/2 levels, were monitored, and the maximum relative sensing sensitivities reached to 0.013 K-1 at 297 K. The emissions located in the first biological window (650, 692 and 800 nm) were monitored and the maximum relative sensing sensitivities reached to 0.027 (R692/650) and 0.028 K-1 (R692/800) at 297 K, respectively. These results indicate that Er3+/Tm3+/Yb3+ co-doped NaYF4 phosphors have potential applications for temperature determination in the visible and the first biological window ranges.

Establishment of Silane/GO Multistage Hybrid Interface Layer to Improve Interfacial and Mechanical Properties of Carbon Fiber Reinforced Poly (phthalazinone ether ketone) Thermoplastic Composites.

This study focused on the faint interface bonding between carbon fiber (CF) and poly(phthalazinone ether ketone) (PPEK) thermoplastic, a multistage hybrid interface layer was constructed via the condensation reaction of N-[3-(Trimethoxysilyl)propyl]-N,N,N-trimethylammonium chloride (KHN+) and the electrostatic adsorption of graphene oxide (GO). The influence of the contents of GO (0.2 wt%, 0.4 wt%, 0.6 wt%) on the interfacial properties of composites was explored. FTIR, Raman spectra, XPS tests indicated the successful preparation of CF-KHN+-GO reinforcements. The multistage hybrid interface layer significantly increased fiber surface roughness without surface microstructure destruction. Simultaneously, polarity and wettability are remarkably improved as evidenced by the dynamic contact angle experiment. The interlaminar shear strength (ILSS) and flexural strength of the CF/PPEK composites with 0.4 wt% GO (CF-KHN+-4GO) were 74.57 and 1508 MPa, which was 25.2% and 23.5% higher than that of untreated CF/PPEK composite, respectively. Dynamic mechanical analysis proved that CF/GO/PPEK composites have excellent high-temperature mechanical properties. This study furnishes an unsophisticated and valid strategy to build an interface transition layer with a strong binding force, which would offer a new train of thought in preparing high-performing structural composites.

Enhanced green emissions of Er3+ /Yb3+ co-doped Gd2 (MoO4 )3 by co-excited up-conversion processes.

Improving the emission from rare earth ions doped materials is of great importance to broaden their application in bio-imaging, photovoltaics and temperature sensing. The green emissions of Gd2 (MoO4 )3 :Er3+ /Yb3+ powder upon co-excitation with 980 and 808 nm lasers were investigated in this paper. Distinct enhancement of green emissions was observed compared with single laser excitation. Based on the energy level structure of Er3+ , the enhancement mechanism was discussed. Moreover, the result of temperature-dependent enhancement revealed that the enhancement factor reached its maximum (2.5) as the sample heated to 120°C, which is due to the competition of two major thermal effects acting in the co-excited up-conversion processes. In addition, the same enhancement of green emissions was also observed in Gd2 (MoO4 )3 :Er3+ powder and NaYF4 :Er3+ /Yb3+ powder.