Microstructure and Ferroelectric Properties of (Bi_(0.9)Ho_(0.1))_(3.999)Ti_(2.997)V_(0.003)O_(12) Thin Films Prepared by Sol-gel Method for Nonvolatile Memory

The (Bi0.9Ho0.1)3.999Ti2.997V0.003O12 (BHTV) films have been prepared on Pt/Ti/SiO2/Si substrates by solgel method. The microstructure and ferroelectric properties of the BHTV films were investigated. The BHTV films show a single phase of Bi-layered Aurivillius structure and dense microstructure. The Ho3+/V5+ cosubstitution can effectively improve the ferroelectric properties. The BHTV film exhibits good ferroelectric properties with 2Pr of 47.6℃/cm2, 2Ec of 265 kV/cm (at applied field of 420 kV/cm), dielec...     

Tm,Ho声光调Q激光系统理论与实验研究

利用激光速率方程理论,对Tm,Ho激光系统计算预测得出最佳耦合输出透过率和调Q激光脉冲宽度.实验采用Tm, Ho:LuLF为增益介质,三向侧面泵浦,环形腔声光调Q.选用透过率20%和30%的输出镜作对比.在透过率20%耦合输出时,得到调Q激光脉冲能量最大为58.0 mJ,对应光光转换效率为1.45%;在透过率30%耦合输出时,得到调Q激光脉冲能量最大为62.9 mJ,对应光光转换效率1.57%,并且获得了最大动静比48.7%.激光脉冲宽度在注入能量3.25 J时为417.2 ns.与理论计算结果较为一致.     

Corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets

(Ho,Nd)FeB magnets with different Ho contents were prepared by Ho substitution for part of Nd during the casting process. Effects of Ho contents on the corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets were analyzed by a highly accelerated aging tester, an electrochemical workstation, a microhardness tester, a bending tester, a scanning electron microscope and an X-ray diffractometer. Results show that the addition of Ho can change the main phase structure, optimize the distribution of rare-earth rich (RE-rich) phases in grain boundary, and improve the corrosion resistance and mechanical properties of NdFeB magnets. When the content of Ho increases from 0 to 21.0 wt%, the weight loss of magnets decreases from 2.672 to 0.933 mg/cm², and the microhardness and bending strength increase from 528.74 HV and 374.92 MPa to 633.84 HV and 459.80 MPa, respectively.     

纵向抽运Tm，Ho：YLF微片激光器激光特性的研究

从速率方程理论出发，得到了抽运功率阈值和激光输出功率的解析表达式。通过钛宝石激光器抽运Tm，Ho：YLF微片，获得90mW的2μm波长激光连续输出。得到了抽运功率和输出功率之间的关系以及抽运光与振荡光之间的转换效率关系。同时也给出了温度对激光输出效率的影响。     

多路Cr,Tm,Ho:YAG激光器合光路的设计

在介绍国外四路Cr,Tm,Ho:YAG激光器的基础上,提出了三种四路Cr,Tm,Ho:YAG激光器合光路经光纤输出的方案,并进行了比较,最终确定了基于平面的四路Cr,Tm,Ho:YAG激光器合光路设计方案。在三路情况下,当单脉冲最大注入能量为100J,重频30Hz时,激光器直接输出功率50.17W,光纤末端输出功率35.65W,耦合效率为71%。经文献调研,目前所达到的输出功率处于国内领先水平。     

Li+增强Ho3+/Yb3+:Y2O3纳米晶的上转化发光研究

采用凝胶溶胶法制备了不同浓度的Y2O3:Ho3+/Yb3+/Li+纳米晶,并且系统研究了不同掺杂浓度对上转化荧光现象的影响。首先,通过XRD图形判断了晶体结构的生成,再通过980 nm的激光器和荧光光谱仪测得的光谱图,发现了位于520~579 nm的绿光、635~674 nm的红光等两条很强的可见光,还有一条较弱的位于743~775 nm的近红外发光。最后,通过与能级图比较和分析可以得出:它们分别是5F4/5S2→5I8,5F5→5I8和5F4/5S2→5I7荧光跃迁。可以看出:在掺杂入Li+之后,上转化荧光得到了极大增强。     

Food safety knowledge,attitudes and practices of street food vendors and consumers in Ho Chi Minh city,Vietnam

This study had the major objective of evaluating the food safety knowledge, attitudes and practices of consumers and vendors of street foods in Ho Chi Minh City (MCMC), Vietnam. There were three main surveys performed in this study. A total of 120 consumers and 40 street food vendors from four districts [Binh Thanh (BT), Thu Duc (TD), district 3 (D3) and district 8 (D8)] in HCMC contributed to the study on a voluntary basis. The surveyed consumers had adequate levels of food safety knowledge and attitudes. No significant difference (p > 0.05) occurred between the food safety knowledge levels of the consumers on the basis of gender. However, significant differences (p < 0.05) occurred on the basis of age, education level, food safety training status and location. In contrast, the street vendors had poor food safety knowledge and attitude levels. No significant differences (p > 0.05) were observed in the food safety knowledge levels of the vendors on the basis of gender and age. However, significant differences (p < 0.05) were found on the basis of food safety training status and education level. It was also noted that the vast majority (95%) of the vendors had not received any food safety training. With regards to the practices, it was determined that 52.5% of the vending sites were open air stands without any protection from the sun, wind and dust. 52.5% the vending stalls had no direct access to potable water, while 47.5% did not have adequate hand washing facilities and a further 30% lacked proper waste water and food disposal facilities. In addition, 52.5% of the vendors did not separate raw, partially cooked food and cooked food products. These findings highlighted that street food vendors in HCMC generally have poor food handling practices and most are operating under unhygienic conditions. These results should provide the Vietnamese government with even more reasons to increase their current efforts to improve the safety of street foods and food safety awareness of the consumers.     

2μmTm,Ho∶YLF激光抽运ZnGeP_2光参量振荡技术研究

ZnGeP2晶体具有宽的透明范围(0.7～12μm),较大的非线性系数(d36=75pm/V),最高损伤阈值能量密 度为10J/cm2,较高的热导率(0.18W/(m·K)),因而非常适合作为高功率中红外光参量振荡器(OPO)晶体。理 论上分析了ZnGeP2光参量振荡器相位匹配特性,实现3～5μm连续调谐范围输出的Ⅰ类相位匹配角在52.5～ 55.2°之间。实验上,以15W光纤耦合激光二极管(LD)抽运的2.05μm高重复频率声光调QTm,Ho∶YLF激光 器作为抽运源,其最大平均功率4W,脉冲宽度小于40ns,脉冲重复频率100Hz～10kHz可调。为降低准三能级 系统激光器阈值,提高激光脉冲能量抽取效率,Tm,Ho∶YLF晶体采用液氮制冷方式,工作在77K温度条件下。 非线性频率转换晶体ZnGeP2长15mm,55.7°切割,光参量振荡器谐振腔为平平腔,腔长约20mm。在3.6W的抽 运功率下,脉冲重复频率10kHz,实现了4.1μm附近中红外激光输出,参量光脉冲宽度为20ns,平均输出功率为 0.7W,光 光转换效率为20%,抽运光阈值功率为0.65W。     

Up-Conversion Properties of Oxy-Fluoride Glasses Co-Doped with Ho3+ and Yb3+

Oxy-fluoride glasses with composition of 25SiO2-65PbF2-9.4AlF3-0.1HoF3-0.5YbF3 were prepared. Their up-conversion fluorescence characteristics were investigated by 980 nm laser. Two emission peaks were observed at 540 and 650 nm. The up-conversion mechanism and processes were analyzed. The relationship between pumping power and relative intensity of emissions was discussed. From the dependence, it is known that the emissions centered at 540 and 650 nm are both attributed to two-photon process.     

Spectroscopy and upconversion processes in YAlO3:Ho crystals

Emission from the high lying excited states, energy transfer, and upconversion processes are investigated in YAlO₃:Ho³⁺. Selectively excited emission spectra in the range from 300 to 800 nm starting from the ³D₃, ³G₅, ⁵F₃, ⁵S₂ and ⁵F₅ multiplets were measured at 15 K. This, together with the detailed absorption and excitation measurements at 15 K allowed determination of the Stark energy levels of Ho³⁺ ions in YAlO₃ up to UV energies. The ⁵S₂ fluorescence decays were recorded as a function of temperature and Ho³⁺ concentration in order to investigate the process of quenching of fluorescence due to cross relaxation among two ions. Conversion of red and infrared laser radiation to green ⁵S₂ and blue ⁵F₃ emission is reported. Under pulsed resonant excitation of the ⁵F₅ or ⁵I₅ levels the upconversion was found to be due to energy transfer process between two excited ions. The photon avalanche effect was observed under cw excitation around 585 nm.