PbF_(2)·SiO_(2)基玻璃陶瓷的溶胶-凝胶法制备及结构转变研究

采用溶胶-凝胶法制备了 PbF2?SiO2纳米晶玻璃陶瓷块体;利用 TG-DSC 和 IR 技术分析了干凝胶在热处理过程中有机基团的分解及内部原子键合方式的演变;结合 XRD 和 TEM 研究了凝胶玻璃中 PbF2纳米晶粒的长大过程,并分析了 Er3+掺杂的影响。结果表明,采用此方法制备的 PbF2?SiO2纳米晶玻璃陶瓷具有较好的成形性,晶化温度在 320℃左右;经 480℃热处理,镶嵌在玻璃基体中的 PbF2晶粒尺度约为 10～25nm,材料透明性良好。在 PbF2?SiO2系统中掺入少量的 Er3+,将提高 PbF2的晶化温度,降低玻璃陶瓷的显微硬度;掺杂可能对 PbF2晶粒表面原子的活性起抑制作用,阻碍晶粒的表面迁移,使晶粒的生长速度明显降低。

新型中红外激光晶体Er^(3+)/Ho^(3+)/Eu^(3+)∶PbF_(2)的生长和性能

采用垂直布里奇曼法成功生长了Er^(3+)/Ho^(3+)/Eu^(3+)三掺杂PbF_(2)的中红外激光晶体。该晶体在980 nm泵浦下,首次获得了从2600~3200 nm的宽带中红外发光,其半高宽(FWHM)为300 nm,这是Er^(3+)的2.7μm发射峰(2600~2950 nm)和Ho^(3+)的2.9μm发射峰(2800~3200 nm)叠加的结果。此外,失活离子Eu^(3+)的引入可以有效克服Er^(3+)和Ho^(3+)离子的自终止瓶颈效应。研究发现,与Er^(3+)/Ho^(3+)∶PbF_(2)晶体相比,Er^(3+)/Ho^(3+)/Eu^(3+)∶PbF_(2)晶体具有更高的荧光分支比,在Er^(3+):^(4)I_(11/2)→^(4)I_(13/2)跃迁为18.7%和Ho^(3+):^(5)I_(6)→^(5)I_(7)跃迁为18.0%;以及有更大的发射截面,在2745 nm时为0.621×10^(-20) cm^(2),在2905 nm时为0.728×10^(-20) cm^(2)。这些有利的光谱特性表明,Er^(3+)/Ho^(3+)/Eu^(3+)∶PbF_(2)晶体在商用980 nm激光二极管泵浦下,可能是2.6~3.2μm中红外激光器的一种有前景的材料。

多种形貌PbF_(2)纳米材料的制备与表征

采用超声乳液法,以PVP-K30(聚乙烯吡咯烷酮)为软模板,调控其加入量制备了多种形貌的α-PbF_(2)纳米材料。采用X-射线粉末衍射、透射电镜等对产物的结构和形貌进行了表征。结果表明,制备的α-PbF_(2)材料具有棒、片、块等形貌。随着PVP-K30由0逐渐增加到4 g,α-PbF_(2)的形貌由一维棒状变为二维的片状、再到三维的块状。讨论了在微乳液体系中,PVP-K30用量对α-PbF_(2)形貌尺寸的控制机理,并研究了α-PbF_(2)在室温下的荧光性质。

Influence of Nd^(3+) concentration on mid-infrared emission in PbF_(2) crystal co-doped with Ho^(3+) and Nd^(3+) ions

A promising series of Ho_(y)Nd_(x)Pb_((1-x-y))F_2(x = 0, 0.01, 0.02, 0.03, 0.04;y = 0.02) crystals was grown by the Bridgman method. The influence of the Nd^(3+)ions concentration on mid-infrared(~2.0, ~2.9 and ~3.9 μm)fluorescence emissions of Ho^(3+)ions in the PbF_(2) crystal excited by 808 nm laser diode was investigated in this work. The energy transfer mechanism between Nd^(3+)ions and Ho~(3+)ions under different concentrations of the Nd^(3+)ions was systematically analyzed. The results show that the Nd^(3+)ions have good sensitization and deactivation effect on the Ho^(3+)ions to stimulate the mid-infrared fluorescence emissions. The experimental analysis proves that the sensitization efficiency of the Nd^(3+)ions is relatively stable at around 93.45% with varying Nd^(3+)-doping concentrations. Concentration dependence studies indicate that the concentration of the Nd^(3+)ions has significant influence on mid-infrared emissions.When the doping concentration of the Nd^(3+)ions is up to 2.0 at%, the intensity of ~2.0, ~2.9 and ~3.9 μm emissions all reach the maximum. The output characteristics of a 3.9 μm laser are simulated, and it is found that with the increase of the Nd^(3+)-doping concentration, the peak power, pulse width, and peak energy all meet the trend of first increasing and then decreasing, and Ho_(0.02)Nd_(0.02)Pb_(0.96)F_(2) crystal displays the best performance. All the results show that the Nd^(3+)/Ho^(3+)co-doped PbF_(2) crystals might act as a useful optical medium for mid-infrared laser applications.

Geant4 application for efficiency simulation of PbF2 based calorimeters

Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter efficiency and measure the particles'energies,momenta and interaction time to detect the particles.This application should become the basis for a new technology of positron emission tomography.Methods To solve the problem,a new C++application based on Geant4 simulation toolkit has been developed.To monitor the response of calorimeters to different types of primary particles,we used different auxiliary Geant4 classes.In addition,we compare the simulation results for the detectors of three different setups,taking into account the detection of both electrons and gamma-quanta,and analyze their efficiency.To evaluate the capability of calorimeters to work under radiation load,we use an experimentally measured transmission function of radiation-damaged PbF_(2).Results Three calorimeter setups exploiting PbF_(2)were simulated with a new C++application based on Geant4.We showed that such type of calorimeter has an energy resolution of 4.1%√E^(e+)[GeV]and good linearity of response for GeV positrons measurements.The efficiency of such structures is found to be approximately 20%for gamma photons’detection.The multilayered structure based on gamma-quanta detection has been proven to be more efficient.It was shown that for the total ionizing dose of 30 krad the Cherenkov light yield decreases by up to two times for 14 cm long PbF_(2)crystals,while for the shorter ones(2.5 and 1.5 cm)this effect is almost negligible.Conclusions We present a new user application in Geant4 for fast simulation of complex structures designed for detection of different high-energy neutral and charged particles.Simulation of calorimeter interaction with 10^(3) of 3 GeV positrons takes 20 min on usual laptop,while for 105511 keV gamma photons it takes 1 min on average.This application allows one to evaluate the efficiency of electromagnetic calorimeters exploiting lead fluoride crystals.Our results pave the way for advanced particle energy measurements,including those used in rapidly developing medical applications such as positron emission tomography,single-photon emission computed tomography etc.

中红外宽带发射氟化铅激光晶体性能研究

中红外激光在光电对抗、激光雷达、遥感探测、激光手术、光纤通信、科学研究等领域中有着非常重要的应用。中红外激光增益材料作为中红外激光器的核心工作介质,具有举足轻重的地位。其中,设计和生长既满足当前泵浦条件又具有高效中红外荧光发射性能的激光晶体成为了研究热点。从优化中红外发光离子光谱性能角度出发,回顾了本课题组近年来关于新型宽带发射稀土离子掺杂氟化铅中红外激光晶体的研究结果,以期为后续研究提供一定的参考。

Simulation research on time resolution based on Cherenkov radiation

Purpose A faster time performance can be achieved by focusing on prompt emitted photons,such as Cherenkov photons.In this study,the time fluctuations of Cherenkov photons transmission in the three Cherenkov radiators were first simulated,and we evaluated the detector performance and discussed ways to improve the coincidence time resolution(CTR)results for the detector with the three radiators.Finally,we compared detection efficiency of Cherenkov radiation in three radiators.Methods In this work,we recorded the step-by-step information of Cherenkov photons and the electrons that produced them in the radiator,information of photons on the photon outputting surface,and the step-by-step information tracing of the par-ent charged particles(electrons)to evaluate the factors influencing the performance time of the detector based on Geant4.Specially,we usually use a photon amplitude timing in the experimental implements,and the arrival time of an event is defined as the arrival time of the first photon of the event accordingly.Results The time fluctuations of Cherenkov photons transmission in the three Cherenkov radiators with a 5 mm length were simulated as 28.5 ps for PbF,40.1 ps for PbWO_(4),and 24.7 ps for Al_(2)O_(3).After considering other factors such as quantum efficiency(QE)of 30%and transit time spread(TTS)of 10 ps from the process of practical electronics,the CTR of a pair of single-pixel detectors were 56.6 ps for PbF_(2),78.8 ps for PbWO_(4),and 46.3 ps for Al_(2)O_(3) with a thickness of 5 mm.The detection efficiency of PbF_(2) is 32.25%,PbWO_(4) of 31.91%and Al_(2)O_(3) of 8.14%in the case of 5 mm length.Conclusions The simulation results indicated that using the Cherenkov photons produced in PbF_(2),PbWO_(4),Al_(2)O_(3) for detec-tor timing can obtain good CTR results.In this study,it demonstrates that it is possible to achieve a pretty good CTR with an improved QE and a reduced TTS of the photodetector.