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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]

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]

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]

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]