外加氩气流下脉冲激光烧蚀制备纳米硅晶粒成核生长动力学研究

为研究纳米硅晶粒成核生长动力学过程,采用脉冲激光烧蚀(PLA)技术,在室温,50～200 Pa的氩气氛围中,通过引入垂直于烧蚀羽辉轴线的外加气流,在水平放置的衬底上沉积了一系列纳米Si晶薄膜.扫描电子显微镜( SEM)、拉曼(Raman)散射和X射线衍射(XRD)检测结果表明,未引入气流时,衬底上相同位置处晶粒尺寸随气体压强的增大逐渐减小;在距靶1 ～2cm范围内引入气流后,尺寸变化规律与未引入气流时相反.通过分析晶粒尺寸及其在衬底上的位置分布特点,结合流体力学模型和热动力学方程,分析得出在激光能量密度一定的条件下,环境气体压强、烧蚀粒子温度和密度共同影响着纳米晶粒的成核生长.     

脉冲时间间隔对激光烧蚀Si粒子密度分布的影响

采用Monte Carlo方法,对脉冲激光烧蚀所产生的烧蚀粒子在环境气体中的输运过程进行了数值模拟.研究了不同脉冲时间间隔与交叠区位置振荡幅度之间的关系,结果表明脉冲时间间隔影响了交叠区的振荡强弱,随着脉冲时间间隔的增加,交叠区的振荡幅度减小,脉冲时间间隔为10 μs时达到最小值,而后开始增大.所得结果为进一步研究烧蚀粒子在环境气体中的输运动力学过程提供了理论依据.     

Structural and band tail state photoluminescence properties of amorphous SiC films with different amounts of carbon

Amorphous silicon carbide films are deposited by the plasma enhanced chemical vapour deposition technique,and optical emissions from the near-infrared to the visible are obtained.The optical band gap of the films increases from 1.91 eV to 2.92 eV by increasing the carbon content,and the photoluminescence(PL) peak shifts from 1.51 eV to 2.16 eV.The band tail state PL mechanism is confirmed by analysing the optical band gap,PL intensity,the Stocks shift of the PL,and the Urbach energy of the film.The PL decay times of the samples are in the nanosecond scale,and the dependence of the PL lifetime on the emission energy also supports that the optical emission is related to the radiative recombination in the band tail state.     

利用Ce:KNSBN光折变晶体提高光学图像相关模式识别鉴别率

给出了在相干匹配滤波系统中利用Ce:KNSBN光折变晶体非线性特性实现图像边缘增强光学相关模式识别的理论分析和实验结果。实验中自相关峰半最大值宽度降低了75％，自相关峰与互相关峰的强度比增强了近一倍，自相关峰的边瓣强度和互相关峰的强度得到抑制，系统的信噪比和相关鉴别率得到显著提高。     

轰击阴极的重粒子能量分布

采用蒙特卡罗模拟对氮辉光放电等离子体中轰击极阴的重粒子（N2^ ,N^ ,Nf及N2f）能量分布随放电参数的变化规律进行了研究。结果表明：阴极臂前诸粒子的能量分布取决于粒子被加速的能量和碰撞频率,能量较低的快原子Nf的密度比高能粒子N^ 的密度最近两个量级。在活性氮粒子（N^ ,Nf）产率最高的放电条件下,适当降低放电气压,提高阴极位降和气体温度,有利于两种活性氮粒子（N^ ,Nf）达到阴极。     

ANALYSIS OF F′0+u ION-PAIR STATE OF IODINE

The optical-optical double resonant multiphoton ionization (OODR-MPI) technique and the fluorescent excitation spectroscopy technique have been applied to the study of the F′0⁺_u ion-pair state of iodine. This paper presents OODR-MPI spectrum and fluorescent excitation spectrum of I₂ in the region of 54000-55300cm^-1 by the three-photon resonant, two-photon ionization (1+2+2) and (1+(1+1)+2) processes.     

泵浦光调制对Ce:KNSBN光折变晶体全息存储质量的改善

实验研究了泵浦光斩波、斩波占空比、斩波频率对两波耦合过程及光扇噪声的影响,结果说明斩波调制抑制了光扇噪声,Ce:KNSBN晶体体全息存储再现图像质量得到明显改善.     

Ce3+在LiBaBO3中的发光特性及晶体学格位

采用固相法制备了LiBaBO3:Ce3+发光材料.测得LiBaBO3:Ce3+材料的发射光谱为一不对称的单峰宽谱,主峰位于440 nm;监测440 nm发射峰,可得其激发光谱为一主峰位于370 nm的宽谱.利用van Uitert公式计算了Ce3+取代LiBaBO3中Ba2+时所占晶体学格位,得出438 nm发射带归属于九配位的Ce3+发射,而469 nm发射带起源于八配位的Ce3+发射.研究了Ce3+浓度对LiBaBO3:Ce3+材料发光强度的影响,结果显示,随Ce3+浓度的增大,发光强度呈现先增大后减小的趋势,Ce3+浓度为3mol%时强度最大,造成其浓度猝灭的原因为电偶极-偶极相互作用.引入Li+,Na+或K+可增强LiBaBO3:Ce3+材料的发射强度.利用InGaN管芯(370 nm)激发LiBaBO3:Ce3+材料,获得了很好的蓝白光发射,色坐标为(x=0.291,y=0.297).     

Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals

Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr microcrystals with different dye concentrations is studied by using picosecond time-resolved fluorescence spectroscopy, and the dependences of electron transfer and spectral efficiency sensitization on different conditions are analysed in detail. With the steady spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate adsorbed on AgBr microcrystals are found to shift to red relative to dye monomer. The spectrum of fluorescence has a red shift relative to the absorption peak. With the time-resolved fluorescence spectroscopy, the fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr grains are found to be fitted well by a double-exponential decay function. The fitting curves consist of a fast and a slow component. Because of the large amplitude of the fast component, this fast decay should be attributable mainly to the electron transfer from J-aggregate of dye to a conduction band of AgBr.     

Sr2+和F-对Ca7Si2O8Cl6:Eu2+荧光粉发光性能的影响

采用高温固相法制备了系列蓝绿色Ca7Si2O8Cl6∶Eu2+荧光粉,并对样品进行了XRD分析、发光性能和色参数的测试。结果表明,合成的样品为单相Ca7Si2O8Cl6;在紫外光激发下,样品呈现一个不对称宽峰结构;分别监测这个发射峰,得到一个较宽的激发谱。同时研究了在样品中分别加入Sr2+和F-后荧光粉的激发和发射光谱,得到了这些离子的加入量与样品发光性能的关系,并探究了发生该现象的原因。结果表明,加入Sr2+或F-后可以得到较好的蓝绿色发光材料。