Table of Content

15 August 2024, Volume 53 Issue 8

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Reviews

Research Progress of Wide Bandgap Semiconductor ZnGa₂O₄

LEI Shasha, GONG Qiaorui, ZHAO Chengchun, SUN Xiaohui, HANG Yin

2024, 53(8):  1289-1301. 

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Due to their unique physical and chemical properties, wide bandgap semiconductor materials have shown great potential in the field of optoelectronic devices, and have received more and more research and attention. Zinc gallate (ZnGa₂O₄) is a wide bandgap semiconductor material, showing broad application prospects in the fields of solar-blind ultraviolet photoelectric detection and X-ray detection for its wide bandgap, unique structure and good thermal stability. In this paper, based on the basic structural characteristics of ZnGa₂O₄, the bandgap, photoelectric properties of ZnGa₂O₄, the preparation methods of ZnGa₂O₄ bulk single crystal and thin film are introduced in detail. Combined with the recent research results of domestic and foreign scholars, the application prospects of ZnGa₂O₄ in many fields are summarized, especially the research progress of solar-blind ultraviolet photoelectric detection, memristor, X-ray detection and power devices. Finally, the future development direction of ZnGa₂O₄ is prospected, and it is pointed out that the quality and performance of ZnGa₂O₄materials can be further improved to improve device performance and meet higher level application requirements.

Recent Advances in Biomass-Derived Carbon Materials for Supercapacitors

NIU Lili, WANG Pei, LIU Yanbin, ZHAO Huijuan

2024, 53(8):  1302-1312. 

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Biomass-derived carbon materials represents promising electrode materials for supercapacitors owing to wide range of precursor sources, large specific surface area, intrinsic heteroatom doping, and controllable pore structure. Additionally, increasing attention has been garnered for significant role in alleviating environmental problems, enhancing waste utilization, and promoting sustainable energy storage applications. This paper summarizes recent advances of biomass-derived carbon materials for supercapacitors with focus on main sources of biomass precursors, preparation strategies and nanostructure for biomass-derived carbon. Then, the pore structure, specific surface area and electrochemical performance of biomass carbon constructed by different strategies (carbonization method, activation method and heteroatom doping) are elaborated. The effect of nanoscale pore structure on their performance is emphasized. Finally, the development prospects and main challenges of biochar in supercapacitors are proposed. This review would provide valuable insights for future development and efficient utilization of biomass carbon.

Research Articles

Growth and Photoelectric Properties Characterization of Large-Sized CH₃NH₃PbBr₃ Crystal

SUN Yuanlong, HU Ziyu, ZHENG Guozong

2024, 53(8):  1313-1318. 

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As a new type of semiconductor material, halide perovskite materials has the advantages of low cost and excellent photoelectric conversion performance. Various photoelectric devices based on the halide perovskite materials have begun to be gradually applied. Polycrystalline thin films are still the main research direction, however, they have the disadvantages of disordered morphology and many impurities. In contrast, single crystals have the characteristics of no grain boundaries and low defects. Therefore, the research based on large-size single crystals gained widely concerned. In this paper, a set of internal and external reverse temperature control cycle filtration growth devices was designed. The CH₃NH₃PbBr₃ single crystal with a diameter of more than 60 mm was prepared by the combination of inverse temperature crystallization and seed crystal. The phase, microstructure, and optical and electrical properties of the crystal samples were studied. The crystal belongs to the cubic system with space group of Pm3m. The ultraviolet-visible absorption spectrum shows that the absorption cut-off edge is about 576 nm and the fluorescence emission spectrum peak is 552 nm. The rocking curve shows that the half width at maximum of the crystal (100) plane is 91.42″. The wafer after cutting and polishing is sensitive to photo response, and the on-off ratio is 2.4×10⁴.

Study on Fiber End-Face Coupled Periodically Poled Lithium Niobate (PPLN) Thin Film Waveguide Device

MA Cuiping, CHEN Jiaying, CHEN Huaixi, LIANG Wanguo, WU Qiulin, FENG Xinkai

2024, 53(8):  1319-1325. 

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The feasibility of achieving efficient coupling between an optical fiber and a periodically poled lithium niobate (PPLN) waveguide in an ideal optical system was theoretically analyzed using a finite element simulator. Divergence of single-mode polarization-maintaining fiber and lensed fiber in space was simulated. Direct end-face coupling simulations were conducted for a PPLN ridge waveguide with a cross-sectional size of 10 μm×10 μm and a length of 20 mm, involving two different types of fibers. It is found that despite the lensed fiber achieving a coupling efficiency of up to 95%, its fundamental mode contribution is less than 5%. Given that PPLN frequency-doubling devices primarily rely on the laser’s fundamental mode for operation, this renders the coupling efficiency of the lensed fiber relatively low in practical applications. In contrast, ordinary single-mode fiber exhibits a significantly higher fundamental mode contribution of 93.8%, demonstrating its superior performance. Therefore, this study selects ordinary single-mode fiber for encapsulation testing with PPLN ridge waveguides. The experimental results show that when the maximum pump power output from the fiber amplifier reaches 1.6 W, the calculated input pump power, after deducting the coupling losses between the input fiber and the waveguide, stands at 1.2 W. The fiber-to-waveguide coupling efficiency is 75%, slightly exceeding the currently known advanced value of 72%. At a temperature of 24.8 ℃, with an input power of 1.2 W at the fundamental wavelength of 1 560 nm, the maximum output of frequency-doubled light is 653 mW. The optical-to-optical conversion efficiency reaches 54.4%, with a normalized conversion efficiency of 20.2%/(W·cm²).

Preparation and Ultraviolet Detection Performance Study of Porous n-GaN/p-Zn_xCu_1-xS Heterojunctions

DU Zhiwei, JIA Wei, JIA Kaida, REN Henglei, LI Tianbao, DONG Hailiang, JIA Zhigang, XU Bingshe

2024, 53(8):  1326-1336. 

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In this paper, porous n-GaN thin films with a pore density of 1.51×10¹⁰ cm^-2 and an average pore size of 38 nm were initially prepared by UV-assisted electrochemical etching (UV-EC). Subsequently, a series of Zn_xCu_1-xS composite films, with x values of 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, were deposited on the porous n-GaN films by water bath method. The bandgaps of the porous n-GaN/Zn_xCu_1-xS heterojunctions varied in the range from 2.34 eV to 3.51 eV. Hall test results demonstrate that when x values is less than 1, the Zn_xCu_1-xS composite films exhibit p-type semiconductor properties. Furthermore, increasing the proportion of CuS leads to an improvement in the conductivity of the composite films. Additionally, XPS results confirm that both Cu and Zn possess a +2 valence within the composite films. When Zn_xCu_1-xS forms a heterojunction with porous n-GaN, the energy band structures of both materials interact to create a built-in electric field. This field facilitates the efficient separation of photogenerated electron-hole pairs. Finally, p-n heterojunctions UV detectors were constructed based on these heterostructures. The I-V curve results indicate that these detectors exhibit good rectification characteristics. Notably, the n-GaN/p-Zn_0.4Cu_0.6S detector demonstrates optimal performance. In the dark state, I_{+3 V}/I_{-3 V} is approximately 1.78×10⁵. Under a bias voltage of -3 V and an optical power density of 432 μW/cm² (ultraviolet light at 365 nm), this detector’s photo-to-dark current ratio exceeds 10³, the rise/fall time is 0.09/39.8 ms, responsivity(R) reaches 0.352 A/W, the external quantum efficiency (EQE) stands at 119.6%, and detectivity(D^*) is 3.21×10¹² Jones. The I-t curve results indicate that the porous n-GaN/p-Zn_xCu_1-xS heterojunctions UV detector possesses reproducible performance during the consecutive on-off optical cycling process with reproducible photocurrent response. This study offers valuable theoretical insights and a comprehensive understanding of the physical properties and performance characteristics of these novel heterostructures UV detectors.

Analysis of the Role of Periodic Reflective Structures and Electron Blocking Layer Setup in Micro-Nano GaN-Based VCSEL

ZHU Zhenyu, JIA Zhigang, DONG Hailiang, XU Bingshe

2024, 53(8):  1337-1343. 

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The maturation of GaN-based micro-nano structure growth methodologies have forged an innovative frontier in the fabrication of micro-nano GaN-based vertical cavity surface emitting lasers (VCSELs). This study delineates a sophisticated micro-nano VCSEL architecture founded on GaN axial heterostructures in the configuration of nanowires, incorporating Al_0.8Ga_0.2N/In_0.2Ga_0.8N strain-compensated structures as top and bottom distributed Bragg reflector (DBR). Notably, the Al composition in the Al_0.8Ga_0.2N layer far surpasses that in conventional structures, enhancing its effectiveness as an electron barrier, obviating the need for the electron blocking layer (EBL) traditionally employed as an electron-blocking mechanism. Furthermore, the influence of EBL on hole injection is meticulously examined. In pursuit of refining the hole injection efficiency of GaN-based VCSELs, a numerical model featuring EBL at distinct positions is formulated using commercial software PICS3D, followed by numerical simulations and analyses that delve into the intricate physical mechanisms. The results underscore that the integration of a strain-compensated DBR, comprised of Al_0.8Ga_0.2N and In_0.2Ga_0.8N, coupled with the elimination of EBL in traditional configurations, markedly enhances hole injection efficiency, thereby optimizing the optoelectronic performance of the device.

Effect of Furnace Air Convection on the Temperature Field of Tellurium Zinc Cadmium Crystal Growth Based on CGSim Simulation

MA Qisi, LIU Jianggao, SHE Weilin, CAO Cong, ZHANG Lichao, ZHAO Chao, FAN Yexia, ZHOU Zhenqi

2024, 53(8):  1344-1351. 

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The growth cycle of tellurium zinc cadmium crystals is long and the growth system is complex. When using vertical Bridgman or vertical gradient freezing methods to grow tellurium zinc cadmium (CdZnTe) crystal materials, the growth process is often difficult to observe intuitively, and there is no corresponding means to detect the temperature field inside the crystals, which brings inconvenience to improve the crystal growth process. In this paper, numerical simulation software is used to analyze the influences of furnace air convection on the temperature field of CdZnTe crystal growth. By opening holes at the top and bottom of furnace, gas exchanging occurs between the inside and outside of the furnace, thereby regulates the convection behaviors. Before opening holes, the convection rate is slow (only 10^-5 m/s), forming stable convection cells; after opening holes, the convection rate significantly increases (0.25~0.90 m/s), and the convection state changes to laminar flow. Through controlling the aperture size (20~40 mm) in the model, the laminar flow rate can be effectively regulated. At the same temperature setting, when the flow rate increases from 0.25 m/s to 0.90 m/s, the temperature gradient will increase from 0.5 K/mm to 1.1 K/mm. Furthermore, experimental work is applied on real furnace, the change of temperature filed before and after opening holes were studied. The experimental results of temperature gradient is accord with the simulating results. It is also found that under laminar flow state, increasing convection rate may improve the stability of temperature field. The increase of temperature gradient and the improvement of stability in the temperature field will be beneficial for the preparation of high-quality CdZnTe crystals.

Effect of Al Doping on the Optical Properties of β-Ga₂O₃ Thin Films

ZHONG Qiongli, WANG Xu, MA Kui, YANG Fashun

2024, 53(8):  1352-1360. 

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In recent years, semiconductor devices are developing towards high heat dissipation, high breakdown field strength and low energy consumption, so the ultra-wide band semiconductor material β-Ga₂O₃ has a broad application prospect. However, effective doping is the basis for realizing β-Ga₂O₃ devices. In this paper, Ga₂O₃/Al/Ga₂O₃/Al/Ga₂O₃ composite structure is experimentally prepared by magnetron sputtering, and the Al atoms are thermally diffused into the film by high-temperature annealing at the same time, so as to form Al-doped β-Ga₂O₃ thin film. Then, the laser zone melting method was used to melt and recrystallize the film area to further enhance the doping quality. The Al-doped β-Ga₂O₃ thin films were tested and characterized in terms of crystal properties, impurity content and optical properties. The experimental results show that: Al doping basically does not change the crystal structure of β-Ga₂O₃ thin films; the impurity content is gradually enhanced as the sputtering time of the Al layer becomes longer; in terms of the optical properties, the ultraviolet (UV) absorptivity of the films is 40% and 50% when the Al sputtering time is 5 and 10 s, and the UV absorption of the Al-doped β-Ga₂O₃ thin films is gradually enhanced with the increase of Al sputtering time; the light absorption of β-Ga₂O₃ thin film is close to 90% when the Al sputtering time is 300 s; and the low concentration of Al doping leads to the narrowing of the band gap width of β-Ga₂O₃ thin film.

Simulation Study on Frequency Characteristics of AlN/β-Ga₂O₃ HEMT

HE Xiaomin, TANG Peizheng, LIU Ruoqi, SONG Xinyang, HU Jichao, SU Han

2024, 53(8):  1361-1368. 

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The influence of frequency characteristics of devices is complex. The effects of AlN barrier thickness, gate length, gate-drain spacing and work function on the frequency characteristics of AlN/β-Ga₂O₃ high electron mobility transistor (HEMT) were studied by Sentaurus TCAD in this paper. The following conclusions are obtained: as the thickness of the AlN barrier layer increases from 10 nm to 25 nm, the cutoff frequency (f_T) and maximum oscillation frequency (f_max) rise by 18 and 17 GHz respectively. The decrease of gate capacitance is the main reason for the increase of f_T. Furthermore, it was found that the thinner barrier layer enhanced the gate’s ability to control the channel electrons. When the gate length is scaled down from 0.9 μm to 0.1 μm, f_T and f_max increase by 84 and 98 GHz, respectively, representing a far more profound influence on frequency characteristics than the barrier layer thickness. However, when the gate length fell below 0.1 μm, short-channel effects emerged. As the gate-drain spacing increase, f_T exhibits a slight decrease. Coupled with the concurrent reduction in source resistance, this led to a synchronized trend in f_max and f_T only when the gate-source voltage (V_GS) exceeds -1.2 V. The work function, on the other hand, has minimal impacts on f_T and f_max, but an increase in the work function positively influenced the device’s pinch-off characteristics. In summary, this paper indicates that by shortening the gate length while concurrently augmenting the thickness of the AlN barrier layer, gate-drain spacing, and work function, one can enhance the frequency characteristics while also improving the pinch-off characteristics of the device, which has certain guiding significance for the design of HEMT devices.

Simulation Analysis and Experimental Research on the Fracture Strength of Photovoltaic Monocrystalline Silicon Slicing Wafers

TAN Huiying, XING Xu, GE Peiqi, BI Wenbo

2024, 53(8):  1369-1377. 

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Monocrystalline silicon is widely used in the photovoltaic industry. As the thickness of wafer processing gradually decreases and the wire saw diameter becomes smaller, phenomena such as adhesion during the slicing process lead to bending or even breaking of the photovoltaic monocrystalline silicon slices, which in turn increases the breakage rate and significantly impacts the cost of photovoltaic solar cells. This study focuses on the cutting process of photovoltaic monocrystalline silicon wafers, using a three-axis bending experiment to measure and analyze the fracture strength and corresponding breakage rate of the silicon wafers. A three-dimensional simulation analysis model for the fracture strength of the silicon slicing wafers was established by finite element method. The research results show that the fracture strength of the silicon slicing wafers has a large dispersion, the average fracture strength is 97.7 MPa. The bending stiffness of the silicon slicing wafers decreases as the thickness decreases, with an average bending stiffness of 441.2 N/m. When the thickness is 60 μm, the bending stiffness is the lowest at 103.5 N/m. The range of wafer breakage rate increases with the decrease of thickness, and the range of wafer breakage rate of 60 μm thickness is the largest, ranging from 0.6% to 99.9%. Simulation and experimental results are basically consistent, indicating that the simulation model and method are suitable for the simulation and analysis of the fracture strength and breakage rate of photovoltaic monocrystalline silicon slices.

Electronic Structure and Magnetic Properties of the Bulk and (001) Surface of Heusler Alloy Mn₂LiGe

SUN Liang, ZHANG Yu, WANG Qun

2024, 53(8):  1378-1385. 

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Using first-principles calculations based on density-functional theory, this paper investigates the electronic structure and magnetic properties of the Heusler alloy Mn₂LiGe bulk and its (001) surfaces. The Mn₂LiGe bulk is demonstrated to be inverse Heusler alloy with space group of F43m and lattice constant of 5.87 Å. A direct band gap with a width of 1.1 eV near the Fermi surface of the spin-down channel is detected. The Mn₂LiGe bulk possesses stable half-metallic and magnetism in the lattice constant range of 5.55~6.33 Å. In addition, six different surface structures of Mn₂LiGe are constructed in this paper. The first layer atoms on the surface undergo different displacements, increasing the surface roughness. Due to surface effects, the magnetic properties of atoms on the surface are different compared to those in the bulk. Both the Mn^AMn^A and Mn^BMn^B surface structures have the highest magnetic moments, while the LiLi and the GeGe surface structures have the lowest magnetic moments. Electronic structure calculations show that the half-metallic band gap present in the bulk is destroyed in all six surface structures and the spin polarization is weakened in varying degrees. Only the LiLi surface structure maintains up to 99.9% of the surface spin polarization, making the surface an excellent prospect for applications in spintronic devices.

First-Principles Study on the Electronic and Magnetic Properties of MXene 2D Material CrVCF₂

LIU Xiaoying, HUANG Haishen, SUN Li, PAN Mengmei, SHANG Zhenzhen

2024, 53(8):  1386-1393. 

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The effects of —F functional group on the structure, electronic properties and magnetic properties of Janus-type MXene 2D material CrVC were studied by first-principles of density functional theory. The calculation results indicate that the —F functional group changes the electronic properties and magnetic properties of CrVC. The nine possible structures of CrVCF₂ exhibit ferromagnetic behavior, among which the structure of CrVCF₂-33 has the lowest energy and is the ground state, with a magnetic moment of 5.01 μ_B and a band gap of 0.099 eV, exhibiting semiconductor characteristics. The total magnetic moment of CrVCF₂-33 remains unchanged when -4%~+4% biaxial strain is applied; the energy increases with either compression or tension strain, but the change is less than 0.2 eV; the band gap changes under the action of strain, when the tensile strain is 2.4%, the band gap decreases to 0.005 eV, which is close to zero. It can be considered a spin-zero band gap semiconductor. The results show that moderate strain can adjust the electronic structure of the CrVCF₂ material, and it can even become a spin-zero band gap semiconductor, indicating its potential application value in the field of spintronics.

Simulation on ZnS/SnS Solar Cells with Spiro-OMeTAD as Hole Transport Layer

TANG Huazhu, XIAO Qingquan, FU Shasha, XIE Quan

2024, 53(8):  1394-1408. 

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Stannous sulfide (SnS) was investigated as an absorbing layer for solar cells due to its suitable electrical and optical properties. Spiro-OMeTAD is commonly employed as a hole transport layer to enhance the performance of solar cells. The ZnS/SnS/Spiro-OMeTAD solar cell was designed and simulated by the wxAMPS software. The effects of the Spiro-OMeTAD hole transport layer on the properties of solar cells were mainly studied, namely the effects on open-circuit voltage, short-circuit current density, filling factor, photoelectric conversion efficiency and quantum efficiency. The results show that the open-circuit voltage of the ZnS/SnS/Spiro-OMeTAD solar cells increase to 0.958 V and short-circuit current increase to 32.96 mA/cm² when the Spiro-OMeTAD HTL is added. The fill factor and photoelectric conversion efficiency are 79.26% and 25.07%, respectively. The performance of the solar cells depends on the thickness of each layer, doping concentration, Gaussian defect state density, and temperature. The results demonstrate that the Spiro-OMeTAD, as a hole transport layer, is beneficial for enhancing various performance aspects of solar cells. Moreover, the ZnS/SnS/Spiro-OMeTAD exhibits a great potential as a photovoltaic device structure.

Synthesis, Crystal Structure and Quantum Chemistry Study on [Co^Ⅲ(DIEN)(N₃)₃] Complex

CHENG Jiajia, WU Mengqi, YANG Min, WANG Limei, WEI Rongmin

2024, 53(8):  1409-1415. 

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Adopting ligand occupation strategy and the principle of molecular self-assembly, a mononuclear cobalt(Ⅲ) complex [Co^Ⅲ(DIEN)(N₃)₃] (1, DIEN=diethylenetriamine) was synthesized by solution method using diethylenetriamine as the organic ligand and Co³⁺ as the central metal ion at room temperature. Single crystal of complex 1 was obtained. The structural characterization and electronic structure analysis were carried out through X-ray single crystal diffraction, elemental analysis, and quantum chemical calculations. Single crystal X-ray diffraction analysis reveals that complex 1 is triclinic, space group of P1 with a=0.825 3(2) nm, b=0.892 0(3) nm, c=0.898 7(3) nm, α=106.497(4)°, β=90.281(4)°, γ=113.861(4)°, V=0.574 7(3) nm³. The central ion Co(Ⅲ) has an elongated octahedral configuration. Each complex is composed of Co³⁺ cation, three azide anions and one diethylenetriamine ligand. A disordered azide anion has a site occupancy of 50%, and 1D chain-like supermolecular was formed by N—H…N hydrogen bond and π…π packing interations. In addition, based on crystal structure of complex 1 determined by X-ray crystallographic analysis, the full geometry optimized and frequency calculations have been performed by density functional theory. The single-point energy, atomic charges and frontier molecular orbital were analyzed. The theoretical calculation results indicate that the complex configuration is stable and consistent with the experimental results.

Preparation of Yellow-Emitting Pure Zn₃V₂O₈ Phosphors and Its Optical Properties

DONG Yujuan, LIU Zhaojiang, ZHU Qirui

2024, 53(8):  1416-1421. 

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Yellow-emitting pure Zn₃V₂O₈ phosphors were successfully synthesized via a simple high-temperature solid-state method using BaF₂ as heat-assisted co-solvent. The purity of Zn₃V₂O₈ was determined by X-ray diffraction (XRD), and its optical properties were analyzed by PLE/PL spectrum, thermal quenching spectrum and fluorescence lifetime curve analysis. The results show that Zn₃V₂O₈ exhibits strong broadband emission in the range of 400~800 nm under the excitation of 360 nm, which is attributed to ³T₂→¹A₁ and ³T₁→¹A₁transition. Zn₃V₂O₈ can emit bright yellow light and the optimum emission wavelength is 550 nm. Under 550 nm, Zn₃V₂O₈ phosphors show wide absorption bands in the range of 200~450 nm. The decay time of Zn₃V₂O₈phosphor is 1.67 ms and its inner quantum efficiency reaches 47.09% at room temperature. Moreover, when the temperature rose to 140 ℃, its emission intensity retention could reach 25.1% of its initial intensity at room temperature, which is higher than that of other garnet structure vanadate materials. Therefore, Zn₃V₂O₈ phosphor as a novel yellow light source for white light-emitting diode devices has potential advantages in terms of low cost and the ability to be mass-produced.

Study on Tunable Blue-Green Luminescence and Mechanism of Tb³⁺ Doped Vanadium Phosphate

ZHANG Shouchao, GAO Sendan, LIU Hongfei, JIANG Rongyun, WANG Cuihong, NIE Xiaoju, ZHANG Liwen, QIN Bing

2024, 53(8):  1422-1433. 

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YVO₄, YPO₄ and YV_1-xP_xO₄ phosphors with various Tb³⁺ doping concentrations were prepared by high-temperature solid-state method. Differential scanning calorimetry (DSC) measurements were conducted to evaluate the chemical reactions during synthesis process, determining 1 350 ℃ as the optimal synthesis temperature. X-ray diffraction (XRD) analysis of the synthesized materials confirmed a tetragonal crystal structure for all samples. The luminescent properties of the mentioned phosphors at room temperature were investigated. Under ultraviolet excitation, luminescence in YVO₄∶Tb³⁺ predominantly arises from the ⁵D₃→⁷F_J (J=6, 5, 4, 2) transitions, resulting in blue emission. The introduction of P element modified the crystal field environment in YV_1-xP_xO₄∶Tb³⁺, enhancing multi-phonon relaxation (MPR) and cross-relaxation (CR) between ⁵D₃ and ⁵D₄ energy levels. With increasing P element content, the emission gradually shifted towards ⁵D₄→⁷F_J′ (J′=6, 5, 4, 3), displaying blue, cyan, and green emissions. In YPO₄∶Tb³⁺, higher doping concentrations enhanced cross relaxation between ⁵D₃ and ⁵D₄ energy levels of Tb³⁺, leading to weakened ⁵D₃ luminescence and intensified ⁵D₄ luminescence. Fine-tuning the doping concentration enabled the control of luminescence from blue to green. In conclusion, by adjusting the matrix composition and doping concentration, the blue-green luminescence modulation of Tb³⁺-doped vanadium phosphate system can be achieved.

High Precision Temperature Monitoring of Substation Equipment Based on NaErF₄@NaYF₄ Upconversion Material

YANG Fan, ZHANG Li, LI Chuhan, CHEN Mingyue, MA Zhizhen

2024, 53(8):  1434-1442. 

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Real-time monitoring of temperature changes in substation equipment is crucial for preventing failures and ensuring a stable power supply. Currently, temperature monitoring of substation equipment primarily relies on manual infrared thermometry, which has limitations such as strong operational dependence, susceptibility to interference, and difficulty in detecting internal faults. The luminous intensity ratio (LIR) is a stable optical parameter unaffected by factors such as spectral loss and environmental influences, making it suitable for temperature detection. The multi-emission characteristics of rare-earth-doped upconversion (UC) materials are highly compatible with LIR technology, demonstrating their potential in high-precision temperature monitoring. Here we introduces a non-contact temperature monitoring method for substation equipment based on NaErF₄@NaYF₄ core-shell UC materials and LIR technique. Experiments show that the method has high accuracy and sensitivity within temperature range of 25 ℃ to 225 ℃, with a sensitivity as high as 35×10^-3 ℃^-1, effectively monitoring temperature changes both inside and outside the equipment. This provides a new technical solution for temperature monitoring of substation equipment.

Preparation and Performance of BiOCl/UiO-66-NH₂ Composite Photocatalytic Materials

JIE Yingze, WANG Yingge, ZHANG Weike, YANG Yanqing

2024, 53(8):  1443-1452. 

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A BiOCl/UiO-66-NH₂ composite photocatalyst was successfully synthesized by solvothermal method and characterized in detail for its morphology, structure, and photocatalytic performance via X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and N₂ adsorption-desorption Brunauer-Emmett-Teller (BET) analysis. The results show that the UiO-66-NH₂ particles are uniformly embedded on the flower-like BiOCl structure, forming a close-contact interface. The composite photocatalyst exhibits excellent photocatalytic performance for the degradation of rhodamine B (RhB) under visible light irradiation. It could completely remove RhB from the solution within 40 min of visible light irradiation, and degradation ability is 3.53 times higher than that of pure BiOCl. The enhancement of photocatalytic activity is attributed to the formation of a Z-scheme heterojunction between BiOCl and UiO-66-NH₂, which facilitated efficient separation and transfer of photogenerated charge carriers. Moreover, the composite photocatalyst exhibits excellent stability with a RhB degradation rate of over 90% after four consecutive cycles.

Effect of Substrate Temperature on Comprehensive Electrochromic Properties of Magnetron Sputtered NiO_x Films

CAI Xiaojia, HUANG Jiajian, SUN Dandan, LIANG Jiaying, TANG Xiufeng, ZHANG Jiong

2024, 53(8):  1453-1463. 

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In order to study the effect of the substrate temperature on the electrochromic properties of NiO_x film, DC reaction magnetron sputtering method was used to prepare NiO_x film at different substrate temperatures, i.e, room temperature, 50, 100, 200 and 300 ℃. The properties of the films including structure and morphology, cyclic stability, optical modulation rate, memory effect, response time, and adhesion to the substrate were explored and compared. The results show that the effect of the substrate temperature on the electrochromic properties of NiO_x film is complicated. NiO_x film prepared at 100 ℃ shows low charge capacity density decay rate, good memory effect, fast response speed,high modulation rate and good adhesion to the substrate. This study may have certain reference significance for the design and fabrication of NiO_x-based electrochromic devices.

Effect of Powder Reduction on the Thermoelectric Performance of Cu₂Se

CHEN Jihu, LU Yani

2024, 53(8):  1464-1470. 

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As a typical liquid-like thermoelectric material, Cu₂Se not only has good electrical transport performance, but also has low lattice thermal conductivity. Nanoengineering is an effective method to achieve high thermoelectric properties for thermoelectrics. However, nanoscale Cu₂Se particles are extremely easy to be oxidized in the process of synthesizing, thus affecting its thermoelectric performance. In order to study the effect of powder reduction on the thermoelectric performance of Cu₂Se, nano-sized Cu₂Se powders were synthesized by hydrothermal method. Hydrogen argon mixed gas (hydrogen volume fraction of 5%) and pure argon were used to purge the powders, respectively. Cu₂Se bulk materials with density above 95% were prepared by spark plasma sintering. The results show that the oxygen content of Cu₂Se bulk is significantly reduced after powder reduction, and there is a 41% decrease in thermal conductivity at 800 K, with a 16% increase in ZT value.

Research Express

C₃H₈N₆I₆·3H₂O: A Novel Crystal with Giant Optical Anisotropy

LIN Zheshuai

2024, 53(8):  1471-1472. 

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