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A LaTa7O19(LTO):Er3+/Yb3+ upconversion luminescence (UCL) phosphor with a hexagonal structure was successfully prepared using a molten salt synthesis method using KCl as solvent. Increasing the holding temperature from 825 to 1150 °C, the LTO structure is transformed towards K2LaTa5O15(KLTO). At 1150 °C, the sample is pure phase KLTO:Er3+/Yb3+. Increasing the holding time at 825 °C from 2 to 48 h, the LTO phase first increases and then decreases. Increasing the KCl flux mass at 825 °C for 24 h, the KLTO structure is first transformed towards LTO, then the KLTO structure increases, and LTO:Er3+/Yb3+ grain size decreases. The highest green UCL integral intensity of LTO:Er3+/Yb3+ reached 89% of β-NaYF4:Er3+/Yb3+. The maximum relative temperature sensitivity of 0.866% K−1 is reached by using the luminescence intensity ratio (LIR) technique. LTO:Er3+/Yb3+ phosphors with excellent pure green UCL can be prepared by molten salt with KCl flux, which can be applied in display and temperature sensing. [ABSTRACT FROM AUTHOR]

BiTa7O19:Er3+/Yb3+/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb3+ and Sb5+ can replace the Ta5+ sites in a BiTa7O19 host to form a pure phase. Compared with BiTa7O19:0.1Er3+/0.4Yb3+, polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm−2. This is due to the adjustment of the local lattice structure of BiTa7O19 by the polyvalent Sb. The maximum absolute sensitivity (SA) and relative sensitivity (SR) can be estimated from the UCL variable-temperature spectra as 0.0098 K−1 at 356 K and 0.0078 K−1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa7O19:Er3+/Yb3+/Sb as a temperature sensor. [ABSTRACT FROM AUTHOR]

A series of Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 (CBSPO) phosphors with significant thermal enhancement were successfully prepared using the solid-state method and the thermal-enhancing effect was studied in detail. When the temperature increased from 303 to 723 K, the upconversion luminescence (UCL) emission intensities of 2H11/2 → 4I15/2 and 2H11/2 + 4S3/2 → 4I15/2 of Er3+ in CBSPO:0.1Er3+/0.2Yb3+ were enhanced 22.81 and 10.06 times under 980 nm laser excitation, respectively. Meanwhile, the UCL color of the sample obviously changed from orange to green with the increase in temperature. Furthermore, the UCL thermal enhancement mechanism was demonstrated, which originates from phonon-assisted transitions. In addition, the maximum absolute temperature sensitivity for CBSPO:0.1Er3+/0.2Yb3+ was calculated to be 0.01026 K−1 at 563 K via luminescence intensity ratio (LIR) technology. All the results show that the CBSPO:Er3+/Yb3+ phosphors can be used for safety warning and temperature measurement at high temperatures. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have attracted tremendous interest due to their fascinating physical and chemical properties and promising applications in nano-electronics, where thermal transport plays a vital role in determining the performance of devices. In this paper, we present a first-principles study of the thermal transport properties of monolayer zinc oxide (ZnO), which has potential applications in nano-electronics and thermoelectrics. The thermal conductivity of monolayer ZnO is found to be as low as 4.5 W m−1 K−1 at 300 K, which is dramatically lower than those of bulk ZnO and lots of other 2D materials. A detailed analysis is performed in the framework of Boltzmann transport theory and electronic structure to understand low thermal conductivity. Most surprisingly, the thermal conductivity of monolayer ZnO slowly decreases with temperature and does not follow the conventional 1/T law. This unusual phonon transport behavior arises from the dominant contribution of optical phonon modes to the overall thermal transport in monolayer ZnO, which has been rarely reported in the literature, and the significantly increased specific heat of the high frequency (optical) phonon modes with increasing temperature, both of which compensate the decrease in the phonon relaxation time. Our study highlights the abnormal thermal transport properties of the new 2D material and we anticipate that this research will motivate the experimentalists to further study other physical and chemical properties of monolayer ZnO for its emerging applications in thermoelectrics, thermal circuits, and nano-/opto-electronics. [ABSTRACT FROM AUTHOR]

The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50–70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30–50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe–Ni films. [ABSTRACT FROM AUTHOR]

The problems of the large volume change during Li insertion and extraction and poor high-power performance of SnO2-based electrodes should be solved for their practical application. Herein, a novel SnO2/C hybrid triple-type nanosphere, in which a layer of amorphous carbon was sandwiched between the layers of the SnO2 and carbon composite, has been designed and fabricated by a top-down approach. Due to its special structure, this kind of SnO2-based electrode exhibited a considerable capacitive performance, offering a greatly enhanced cycling stability and rate capability. Its capacity remained as high as 653 mA h g−1 after the 350th cycle. The irreversible capacity decay was unprecedentedly extended to the 80th cycle. What is more, this electrode even exhibited a capacity of 260 mA h g−1 at 20 C, with a fading of less than 16% after 600 cycles and less than 22% even after 1000 cycles. [ABSTRACT FROM AUTHOR]

BiTa 7 O 19 :Er 3+ /Yb 3+ /Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb 3+ and Sb 5+ can replace the Ta 5+ sites in a BiTa 7 O 19 host to form a pure phase. Compared with BiTa 7 O 19 :0.1Er 3+ /0.4Yb 3+ , polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm -2 . This is due to the adjustment of the local lattice structure of BiTa 7 O 19 by the polyvalent Sb. The maximum absolute sensitivity ( S A ) and relative sensitivity ( S R ) can be estimated from the UCL variable-temperature spectra as 0.0098 K -1 at 356 K and 0.0078 K -1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa 7 O 19 :Er 3+ /Yb 3+ /Sb as a temperature sensor.

A series of Er 3+ /Yb 3+ co-doped Cs 3 BiSr(P 2 O 7 ) 2 (CBSPO) phosphors with significant thermal enhancement were successfully prepared using the solid-state method and the thermal-enhancing effect was studied in detail. When the temperature increased from 303 to 723 K, the upconversion luminescence (UCL) emission intensities of 2 H 11/2 → 4 I 15/2 and 2 H 11/2 + 4 S 3/2 → 4 I 15/2 of Er 3+ in CBSPO:0.1Er 3+ /0.2Yb 3+ were enhanced 22.81 and 10.06 times under 980 nm laser excitation, respectively. Meanwhile, the UCL color of the sample obviously changed from orange to green with the increase in temperature. Furthermore, the UCL thermal enhancement mechanism was demonstrated, which originates from phonon-assisted transitions. In addition, the maximum absolute temperature sensitivity for CBSPO:0.1Er 3+ /0.2Yb 3+ was calculated to be 0.01026 K -1 at 563 K via luminescence intensity ratio (LIR) technology. All the results show that the CBSPO:Er 3+ /Yb 3+ phosphors can be used for safety warning and temperature measurement at high temperatures.