Search

Although negative thermal expansion (NTE) materials provide a new strategy to overcome the thermal-quenching phenomenon among rare earth doped luminescent materials, the overall weak upconversion luminescence still restricts their application in the field of optical temperature sensing. Herein, giant enhancement of anti-quenching upconversion luminescence is achieved in the NTE Sc2W3O12:Er3+/Yb3+ phosphors by (KMg)3+ impurity doping, and the phosphors are used for the construction of an all-fiber temperature sensing (AFTS) system. Compared to the upconversion luminescence of the Sc2W3O12:Er3+/Yb3+ phosphors at room temperature, the synergistic effect of impurity doping and NTE characterstics results in a 6000-fold enhancement of the upconversion luminescence of the (KMg)3+ doped Sc2W3O12:Er3+/Yb3+ phosphors at 573 K. A single-point tip temperature sensor was constructed based on the fluorescence luminescence intensity ratio (FIR) technology and the corresponding self-calibrated curves were obtained with a regression coefficient of 0.9996. The potential application of the constructed AFTS system was demonstrated in the real-time temperature monitoring of a CPU chip and a thermostat bath. [ABSTRACT FROM AUTHOR]

Octahedral NaBi(WO4)2:Er3+/Yb3+ phosphors were synthesized by a hydrothermal method. Intense green upconversion emissions from both 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ions were observed and the appropriate energy gap between them is very suitable for temperature sensing requirement based on the fluorescence intensity ratio (FIR) technique. A flexible and portable all-fiber temperature sensing device was established and used to assess the temperature sensing characteristics of NaBi(WO4)2:Er3+Yb3+ phosphors. A maximum absolute sensitivity of 0.014 K−1 is achieved at 423 K and the temperature absolute error is −0.5 K to +0.6 K. The stepwise heating and cooling processes confirm the good stability and recyclability of the all-fiber temperature sensor, which lays the foundation for actual temperature measurement. Based on the high flexibility and accuracy of the temperature sensor, the monitoring of body temperature was realized in real time and continuously, which may provide new development prospects for effective health tracking and improvement of medical care quality. [ABSTRACT FROM AUTHOR]

Accurate and remote temperature measurements in harsh environments are of great importance. The FIR technique is self-referenced and regarded as a promising method to improve the temperature accuracy and simplify the experimental devices. Herein, a point all-fiber temperature sensor based on the FIR technique has been developed. Er3+/Yb3+ co-doped NaYF4 phosphors (NPs) were used to fabricate a temperature sensing probe combined with silica fiber. Highly crystalline and pure hexagonal NPs were synthesized by a hydrothermal method. Intense green up-conversion luminescence was observed in the prototype sensor at an excitation power of 1 mW. The relationship between FIR value and temperature was investigated at the temperature range of 258–423 K. The maximum relative temperature sensitivity is 1.68% K−1 at 258 K. Preliminary experimental results indicate that the absolute error is ±1 K with a temperature uncertainty σ of 0.187 K and relative standard deviation of 0.133%, suggesting the high accuracy and reliability of the proposed all-fiber temperature sensor. [ABSTRACT FROM AUTHOR]

Simultaneous enhancement of upconversion luminescence and temperature sensitivity is achieved by aliovalent doping in Er3+/Yb3+ codoped SrMoO4 phosphors and a highly accurate ratiometric temperature sensing platform has been constructed in an all-fiber structure. The influence of aliovalent doping of Li+ and Ga3+ in SrMoO4 phosphors on the crystal structure and growth was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A detailed structural analysis was carried out using Eu3+ ions as a spectroscopic probe to disclose the change of the local site symmetry due to aliovalent doping. The upconversion emission intensity of Er3+ in SrMoO4 phosphors is enhanced by 82 times and 255 times due to Li+ doping and Li+/Ga3+ codoping, respectively. The intense upconversion luminescence and high temperature sensitivity lead to a small temperature uncertainty (0.091 K) and an absolute error (−0.5–0.3 K) as well as good repeatability (<1%). Preliminary experiments from material design to device applications pave the way for the practical applications of ratiometric temperature sensors. [ABSTRACT FROM AUTHOR]

A portable all-fiber thermometer based on the FIR technique in Er3+/Yb3+ co-doped TeO2–WO3–La2O3–Na2O (TWLN) glasses was designed and its temperature sensing performance in the temperature range of 293–569 K was determined in detail. The high glass transition temperature (Tg = 439 °C) of TWLN glass contributes to broadening the range of temperature measurement. The spectroscopic analysis of Eu3+ ions and Judd–Ofelt analysis of Er3+ ions reveal that the rare earth ions are situated in a low symmetry environment in TWLN glass, which suggests that a large FIR change and high temperature sensitivity are expected. Intense green upconversion emission in Er3+/Yb3+ co-doped TWLN glass fiber was easily observed under 980 nm excitation at a low pumping power (1.4 mW). The maximum temperature sensitivity of the portable all-fiber thermometer reached 86.7 × 10−4 K−1 at 553 K. Experimental results showed that the absolute errors were around ±1 K within the temperature range from 285 to 563 K. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of hexoctahedral (HOH-shaped), elongated tetrahexahedral (ETHH-shaped) and octahedral (OCT-shaped) Au@AuPd nanoparticles (NPs) via co-reduction of a trace amount of Au and Pd precursors by ascorbic acid (AA) with the aid of an elemental silver reservoir on the surface of the corresponding preformed Au NPs enclosed by different facets. Consequently, surface facets of alloy-shells of the resulting Au@AuPd NPs can be tuned, as they can retain the original surface facets of pre-formed, facet-controlled Au cores. It is found that both mass activities and specific activities of the three types of Au@AuPd NPs exhibit “volcano-type” dependence with respect to their Pd content in the surface of ultrathin AuPd alloy-shells. Moreover, HOH-shaped Au@Au0.20Pd2.0 NPs simultaneously display the best activity and excellent stability due to the exposed high-index facets of the AuPd alloy-shell and the appropriate area ratio of active facets and inactive facets on the surfaces of ultrathin alloy-shells. Furthermore, their ECSA value, mass activity and specific activity are 125.8 m2 g−1, 11.9 A mgPd−1 and 9.5 mA cm−2, respectively, which are about 4-fold, 31-fold, and 7-fold better than those (28.4 m2 g−1, 0.38 A mgPd−1, and 1.34 mA cm−2) of commercial Pd/C catalysts, respectively. Thus, this work not only demonstrates that surface facets of core–shell Au@AuPd NPs can be engineered via co-reduction of a trace amount of Au and Pd precursors by AA with the aid of an elemental silver reservoir on the surface of preformed Au NPs, but also will open a new way to improve the electrocatalytic performance of CS Au@AuPd NPs by surface engineering. [ABSTRACT FROM AUTHOR]

We first synthesized high-quality gold nanoparticles (Au NPs) with size ranging from 5.5 to 17.8 nm in high yield via a robust, one-step seeded growth method using Tris-base (TB). It was found that the narrow distribution in size and shape of the as-prepared Au NPs was affected by reaction temperature and pH value of the reaction media. The sizes of these small Au NPs could be finely controlled by varying the gold precursor and/or seed amount according to an established relationship between the NP diameter and the particle number of the seeds (or the mass of the gold precursor in some cases). Due to their highly colloidal stability, TB-stabilized Au NPs (TB-Au NPs) could be directly used for the detection of Pb2+. Pb2+ can be determined in a large linear range of 0.1 nM to 5 μM with a high determination coefficient, good repeatability (10 times at least) and high selectivity (1 : 200) by our 2-mercaptoethanol (2-ME)/S2O32−–TB-Aum NP sensors (m represents the size of Au NPs, m = 5.5, 10, and 15 nm). Moreover, the limit of detection (LOD) of the 2-ME/S2O32−–TB-Au5.5 NP sensor for Pb2+ could be as low as 0.1 nM, which, to the best of our knowledge, is the lowest one obtained by a colorimetric method thus far. Furthermore, our 2-ME/S2O32−–TB-Au5.5 NP sensor could also detect Pb2+ in real soil extracts with satisfactory recovery. Thus, the 2-ME/S2O32−–TB-Au5.5 NP sensor could be applied for the determination of Pb2+ in real samples from complicated natural environments. [ABSTRACT FROM AUTHOR]

In this work, we report the production of hyperbranched, trisoctahedral-shaped core–shell Au@PdPt nanoparticles (HTCS Au@PdPt NPs) by facet-dependent growth of transition Pd layers and uniform PdPt alloy shells, respectively, by two batches of addition of the reducing agent, ascorbic acid (AA) solution, on preformed trisoctahedral (TOH) Au cores enclosed by {331} facets. It is found that the thickness and composition of the PdPt alloy shell of HTCS Au@PdPt NPs can be accurately controlled by varying the amount of the Pd and Pt precursors. Moreover, the ultrasmall PdPt branches (3.5 nm × 9.2 nm) on the TOH Au cores can lead to a significantly increased electrochemically active surface area (up to 55.4 m2 gPt−1). Taking electrooxidation of methanol and formic acid by Au@PdPt catalysts as an example, three types of Au cores enclosed with different facets were selected to investigate the effect of the resulting transition Pd layer on the performance of CS NP-based catalysts with similar structures. By comparison of their electrocatalytic performance, the enhanced electrocatalytic performance of the HTCS Au100@Pd20Pt20 NPs can be mainly attributed to improved charge transfer between the well-defined TOH Au cores and the highly crystalline PdPt alloy shells besides the unique dendritic PdPt alloyed shell and core–shell structure. The as-prepared HTCS Au100@Pd20Pt20 NPs have excellent electrocatalytic performances in electro-oxidation of methanol (0.64 A mgPt−1) and formic acid (0.77 A mgPt−1), which are significantly higher than those of commercial Pt black (0.12 A mgPt−1 for both of methanol and formic acid) and other Au@PdPt NPs with Au cores enclosed with different facets. In addition, HTCS Au100@Pd20Pt20 NPs also exhibit the best durability among them possibly due to their superior anti-CO poisoning capability. [ABSTRACT FROM AUTHOR]

We report one new method for direct synthesis of monodisperse, quasi-spherical AuAg alloyed nanocrystals (ANCs) with sizes of 11 to 25 nm and core–shell (CS) AuAg@AuAg NCs (CS AuAg ANCs) with sizes of 30 to 80 nm via the Fe2+-assisted citrate coreduction of auric ions and silver ions in a one-pot reaction. It is found that at fixed concentration of auric ions, the concentrations of ferrous ions and silver ions play key roles in tuning the size and the types of NCs (AuAg ANCs and CS AuAg ANCs), respectively. Moreover, AuAg ANCs and CS AuAg ANCs exhibit excellent and poor chemical stability in nonideal chemical environments, respectively. The potential application of these AuAg ANCs for SERS detection of industrial pollutants (such as benzidine and p-cresol) in artificial industrial wastewater has been successfully demonstrated. [ABSTRACT FROM AUTHOR]

Cubic-to-hexagonal phase evolution, narrow crystalline size distribution and enhancement of luminescence are simultaneously achieved by modifying the ratio of SiO2/B2O3 content in the Eu3+-doped oxyfluoride borosilicate glass ceramics containing NaGdF4 nanocrystals. The mechanisms of phase evolution of NaGdF4 nanocrystals are discussed on the basis of IR spectra, viscosity, XRD and TEM data. The results indicate that the stresses developed during the thermal treatment process play an important role in the phase evolution, which provides an experimental evidence of pressure-induced disorder-to-order phase evolution during the crystallization process for the first time. It is also found that the excitation and emission spectra as well as the luminescence lifetimes of the Eu3+ ions in the oxyfluoride glass ceramic are sensitive to the crystal lattice of NaGdF4. [ABSTRACT FROM AUTHOR]

An emission-tunable, Eu2+-activated, Ba2Ca(PO4)2:Eu2+ phosphor was synthesized by a conventional solid-state reaction. X-ray powder diffraction (XRD) and FT-IR spectroscopic analysis confirmed the phase formation. Electron paramagnetic resonance (EPR) analysis indicated there are three different crystallographic Ba2+ sites, namely, Ba(1), Ba(2) and Ba(3), occupied by the Eu2+ ions. The excitation and emission spectra, concentration dependence of the emission intensity and decay curves of the phosphor were investigated. The results showed that with increasing Eu2+ concentration, the emission peak wavelength redshifted from 457 to 500 nm, and the color hue can be tuned from a greenish blue to a yellowish green. A white LED was fabricated using a near ultraviolet (n-UV) 410 nm chip pumped with a blend of phosphors consisting of greenish blue-emitting Ba1.97Ca(PO4)2:0.03Eu2+ and red-emitting Ca3.97(PO4)2O:0.07Eu2+. When the applied current was 350 mA, the white LED had Commission International de l'Eclairage color coordinates of (0.3249, 0.3421) at a white light (correlated color temperature = 6020 K) and an excellent color rendering index of 93. [ABSTRACT FROM AUTHOR]

Well-defined nanoporous palladium (np-Pd) fabricated by a modified electrochemical dealloying procedure is demonstrated to be an excellent electrocatalyst material for reductive degradation of both carbon tetrachloride and chlorobenzene. [ABSTRACT FROM AUTHOR]

Octahedral NaBi(WO4)2:Er3+/Yb3+ phosphors were synthesized by a hydrothermal method. Intense green upconversion emissions from both 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ions were observed and the appropriate energy gap between them is very suitable for temperature sensing requirement based on the fluorescence intensity ratio (FIR) technique. A flexible and portable all-fiber temperature sensing device was established and used to assess the temperature sensing characteristics of NaBi(WO4)2:Er3+Yb3+ phosphors. A maximum absolute sensitivity of 0.014 K-1 is achieved at 423 K and the temperature absolute error is -0.5 K to +0.6 K. The stepwise heating and cooling processes confirm the good stability and recyclability of the all-fiber temperature sensor, which lays the foundation for actual temperature measurement. Based on the high flexibility and accuracy of the temperature sensor, the monitoring of body temperature was realized in real time and continuously, which may provide new development prospects for effective health tracking and improvement of medical care quality.