Intermittent investigations on attenuation mechanism of rechargeable zinc-air batteries during charge/discharge cycles.

Rechargeable zinc-air batteries (RZABs) are an ideal substitute for energy storage, but the short cycle longevity during long-term charge/discharge operation is one of the bottleneck factors that seriously restrict commercial application. Herein, the FeCo alloy/N, S co-doped carbon aerogel (NSCA/FeCo) were prepared as catalysts of cathode for RZABs. We investigated the polarization and impedance on long-term cycles during the battery operation to explore the attenuation mechanism. The results indicated that the roundtrip efficiency of batteries during charge/discharge cycles reduced fast initially and then slow. Besides, the comparative experiment was tested through the replacement of a new electrolyte and a zinc sheet. It is manifested that the failure of the battery is mainly due to the attenuation of the air cathode performance. Therefore, to further disclose the influencing factors and internal mechanisms of air cathode performance degradation, we conducted a series of characterization and testing, including the hydrophilicity, surface morphology, elemental composition, and electrochemical performance of three-electrode systems at different cycle times. This work not only provides a theoretical basis for deeply comprehending the attenuation mechanism of the cathode but also serves a reference for the material design and operating condition optimization of RZABs.

Color-tunable luminescence based on the efficient energy transfer of a Tm-Dy system for optical thermometry and white LED lighting.

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10-3 K-1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields.

Winning color-tunable upconversion luminescence and high-sensitive optical thermometry in K3Gd(PO4)2:Yb3+,Er3+,Tm3.

A series of Yb3+, Er3+, Tm3+ co-doped K3Gd(PO4)2 are prepared via the solid-state reaction method. Upon 980 nm excitation, the synthesized samples present color-tunable upconversion luminescence ranging from yellow to blue with the increment of Tm3+ doping contents. The upconversion mechanisms of Yb3+, Er3+, Tm3+ co-doped system are systematically investigated in detail. Varying contents of Tm3+ can appropriately alter the upconversion emissions of blue, green and red via possible energy transfer processes. Furthermore, the thermometric performances of phosphors associated with upconversion luminescence are analyzed in the temperature region of 300-675 K. By employing non-thermally coupled energy levels (2H11/2/4F9/2 of Er3+), the maximum relative and absolute sensitivity reaches 0.78 % K-1 and 0.168 K-1. Combining the sensitivity characteristic and repeatability of thermometer, the luminescence intensity ratio technology based on non-thermally coupled energy levels may be a more effective choice for optical thermometry. These excellent results will pave an avenue to K3Gd(PO4)2:Yb3+,Er3+,Tm3+ phosphors for the fields of color-tunable luminescence and non-contact temperature sensing.

Towards highly efficient NIR II response up-conversion phosphor enabled by long lifetimes of Er3.

The second near-infrared (NIR II) response photon up-conversion (UC) materials show great application prospects in the fields of biology and optical communication. However, it is still an enormous challenge to obtain efficient NIR II response materials. Herein, we develop a series of Er3+ doped ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. ß-NaYS2:Er3+ achieves a visible UC efficiency as high as 2.6%, along with high brightness, spectral stability of lights illumination and temperature. Such efficient UC is dominated by excited state absorption, accompanied by the advantage of long lifetimes (4I9/2, 9.24 ms; 4I13/2, 30.27 ms) of excited state levels of Er3+, instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS2:Er3+ phosphors are further developed for high-performance underwater communication and narrowband NIR photodetectors. Our findings suggest a novel approach for developing NIR II response UC materials, and simulate new applications, eg., simultaneous NIR and visible optical communication.

Synthesis of core-shell nanoparticles based on interfacial energy transfer for red emission and highly sensitive temperature sensing.

Red up-conversion luminescence with both emission and excitation peaks within the "tissue transparency window" makes for ideal fluorescent labels for deep tissue penetration and low-background biological imaging. In this work, an efficient strategy is proposed to realize bright red up-conversion luminescence based on interfacial energy transfer (IET), and the luminescence centers (Er3+ and Tm3+) and sensitizers (Yb3+) are doped in separate layers to avoid deleterious cross-relaxation. The IET process between Yb3+ and Er3+ can enable bright red photon up-conversion under 980 nm excitation via fine control and manipulation of the lanthanide ion concentration and shell thickness. By appropriately employing the fluorescence intensity ratio technique, an optical thermometer based on non-thermally coupled energy levels demonstrates a superior relative sensitivity of 2.02% K-1 across the whole temperature region. NaYF4:Er3+,Tm3+@NaYF4:Yb3+ with strong red UC luminescence and highly sensitive performance exhibits potential for application in the field of non-contact temperature sensing.

Aligned Plasmonic Antenna and Upconversion Nanoparticles toward Polarization-Sensitive Narrowband Photodetection and Imaging at 1550 nm.

Lanthanide-doped upconversion nanoparticles (UCNPs) are rising as prospect nanomaterials for constructing polarization-sensitive narrowband near-infrared (NIR) photodetectors (PDs), which have attracted significant interest in astronomy, object identification, and remote sensing. However, polarized narrowband NIR photodetection and imaging based on UCNPs have yet to be realized. Herein, we demonstrate that NIR photodetection and imaging are capable of sensing polarized light as well as affording wavelength-selective detection at 1550 nm by integrating directional-Au@Ag nanorods (D-Au@Ag NRs) with NaYF4:Er3+@NaYF4 UCNPs. Monolayer and large-area D-Au@Ag NRs polarization-sensitive plasmonic antenna films are obtained, and the center of their localized surface plasmon resonance (LSPR) peak is located at around 1550 nm. Experimental and theoretical results reveal that D-Au@Ag NRs have a sharp localized LSPR peak with a dominant scattering cross section. The UCNPs coupled with D-Au@Ag NRs exhibit significantly enhanced and strongly polarization-dependent luminescence with a high degree of polarization (DOP) of 0.72. The first polarization-resolved UC narrowband PD at 1550 nm is achieved, which delivers a DOP of 0.63, a detectivity of 1.69 × 1010 Jones, and a responsivity of 0.32 A/W. Finally, we develop a polarized imaging system for 1550 nm with visual photoelectric detection based on the aforementioned PDs. Our work opens up possibilities for manipulating UC and developing next-generation polarization-sensitive narrowband infrared photodetection and imaging technology.

High-sensitive temperature sensing based on thermal-enhanced emission and non-thermally coupled energy levels of white upconversion luminescence system.

Na3Y(VO4)2:Nd3+,Yb3+,Ho3+,Tm3+ phosphors present significantly improved sensitivity of optical temperature sensing based on thermal-enhanced upconversion luminescence and non-thermally coupled energy levels. Under 808 nm excitation, white upconversion luminescence is successfully achieved in Nd3+-sensitized system. In addition, the emissions intensities originated from 4G5/2→4I9/2 transition of Nd3+ and 3F2,3→3H6 transition of Tm3+ gradually increase with elevating temperature owning to the thermal population effects, as opposed to the blue (1G4→3H6 transition of Tm3+), green (5S2,5F4→5I8 transition of Ho3+) and red (5F5→5I8 transition of Ho3+) emissions intensities show continuous decreasing trend. The temperature sensing behaviors are investigated by employing multiple non-thermally coupled energy levels. Based on non-thermally coupled energy levels of 4G5/2 (Nd3+)/1G4 (Tm3+), the absolute and relative sensitivities are obtained to be 0.433 K-1 and 2.81 % K-1. These results demonstrate that the Na3Y(VO4)2:Nd3+,Yb3+,Ho3+,Tm3+ phosphors with superior optical thermometry performance and white luminescence within a relatively wide temperature range can achieve optical applications in many fields.