Ag纳米颗粒增强的Ho~(3+)/Tm~(3+)共掺铋锗酸盐玻璃的2μm发光研究

采用基于传统熔融淬冷技术的热化学还原法制备了系列Ag纳米颗粒复合Ho3+/Tm3+共掺铋锗酸盐玻璃样品,研究了Ag纳米颗粒含量对玻璃2μm发光特性的影响.结果表明,Ag纳米颗粒的表面等离子体共振带位于500—900 nm,峰值位于650 nm,透射电子显微镜图像中观察到均匀分布的Ag纳米颗粒,尺寸约为5—10 nm.通过测试玻璃样品在1.7—2.3μm波段的荧光光谱发现,Ag掺杂后Ho3+离子2μm处的荧光强度得到了极大的提高,其中AgCl掺杂质量分数为0.3%时的荧光强度比未掺杂时的荧光强度增强10倍,这归因于Ag纳米颗粒的局域场增强作用.计算得到Ho3+离子的吸收截面为0.491×10-20cm-2,发射截面为1.03×10-20cm-2,当增益系数为0.2时即可实现正的增益.     

Ag纳米晶对Tm/Yb共掺碲酸盐玻璃上转换发光性能的影响

在稀土离子掺杂碲酸盐玻璃中引入Ag纳米晶,通过等离子共振(SPR)可使荧光发射得到增强,上转换发光效率得到明显提升。研究了Ag纳米晶对Tm3+/Yb3+共掺碲酸盐玻璃上转换发光的影响,分析了上转换发光机理。结果发现,经过(330℃,30 min)热处理后,玻璃中析出了Ag纳米颗粒,尺寸为5～8 nm。Ag纳米晶的引入可使玻璃上转换蓝、红光由三光子吸收转变为双光子吸收。由于局域场表面等离子体共振增强以及Ag与Tm3+之间的能量转移,使得含Ag纳米晶玻璃的荧光强度比不含Ag纳米晶的玻璃提高了约5倍。     

可调白光发射的Ce-Tb-Eu共掺钙硼硅酸盐发光玻璃

采用高温熔融法制备了Eu单掺和Ce-Tb-Eu共掺的钙硼硅酸盐发光玻璃。使用荧光分光光度计测量了样品的发射与激发光谱,并通过激发、发射光谱和CIE色度坐标对其发光特性进行了研究。结果表明:改变玻璃基质提高其光学碱度,可以大幅度增加Eu³⁺/Eu²⁺比例,增强Eu³⁺的红光发射。在378 nm单色光激发下,Ce-Tb-Eu共掺发光玻璃的发射光谱中同时观测到了蓝光、绿光和较强的红光特征峰。通过调节Tb、Eu的比例,可以使样品发射光谱的色坐标在白光区域内变化,实现白光调控。     

Eu2+/Dy3+共掺SrSiO3透明微晶玻璃的光学性质

在还原气氛中采用高温熔融法制备了Eu2+-Dy3+共掺硅酸盐玻璃,热处理后得到了Eu2+-Dy3+共掺透明SrSiO3微晶玻璃。测试了样品的激发光谱和发射光谱,研究了不同Eu2+-Dy3+物质的量比下微晶玻璃发光的变化并计算了对应的色坐标。研究发现,样品发射光谱范围在400～600nm,其中400～550nm(绿光)的宽发射谱带来自Eu2+的5d→4f跃迁,而位于483nm(蓝光)和575nm(黄光)的尖峰则来自Dy3+的4F9/2→6 H15/2和4F9/2→6 H13/2跃迁;在紫外(UV)光(365nm)激发下通过调控Eu2+-Dy3+物质的量比可得到发白光的微晶玻璃,当Eu2+-Dy3+物质的量比为1∶8时,Eu2+-Dy3+共掺SrSiO3透明微晶玻璃所发白光最佳,对应的色坐标(0.268,0.356)位于CIE标准色坐标图的白光区域且最接近理想白光。结果表明,Eu2+-Dy3+共掺SrSiO3透明微晶玻璃可作为一种潜在的白光发光二极管用基质材料。     

白光LED用Ce3/Sm3共掺玻璃和微晶玻璃的发光特性及能量传递研究

采用高温熔融法制备了一系列Ce3+/Sm3+共掺透明微晶玻璃,并研究了其发光特性.在微晶玻璃中Ce3+呈现出基于4f 5d跃迁的较强的宽带蓝光发射,通过调节Ce3+/Sm3+离子的掺杂浓度,Ce3+/Sm3+离子共掺微晶玻璃发光的色度逐渐发生变化,当CeO2/Sm2O3掺杂的量比为1∶1时,制得的微晶玻璃发光色坐标为(0.315,0.296).通过光谱和荧光衰减曲线,研究了Ce3+离子到Sm3+离子的能量传递,在SAZKNGC0.6S0.6微晶玻璃中,Ce3+离子向Sm3+离子传递能量效率约为20%.结果表明,Ce3+/Sm3+共掺微晶玻璃是白光LED的一种潜在基质材料     

Sr_3B_2O_6∶Eu~(3+),Li~+荧光粉的合成与发光性能

采用高温固相法合成Sr3B2O6∶Eu3+,Li+红色荧光粉,考察了激活剂Eu3+和电荷补偿剂Li+浓度对Sr3B2O6∶Eu3+,Li+荧光粉发光性能的影响。结果表明:适量掺杂Eu3+、Li+离子并不改变Sr3B2O6的结构。当Eu3+掺杂量为4%、Li+的掺杂量为8%时,在900℃下灼烧2 h可以得到发光性能最佳的Sr2.9B2O6∶0.04Eu3+,0.08Li+红色荧光粉。以394 nm的近紫外光激发时,Sr3B2O6∶Eu3+,Li+荧光粉发射出红光,对应于Eu3+的4f-4f跃迁,其中以614 nm附近的5D0→7F2跃迁发光最强,是一种有潜力用于白光LED的红色荧光粉。     

Dy3+含量对Eu2+,Dy3+共掺高硅氧发光玻璃发光性能的影响

通过控制Dy3+的掺杂浓度,制备出了不同浓度的Eu2+,Dy3+单掺和共掺高硅氧发光玻璃,测试其激发和发射光谱,讨论了Dy3+浓度对Eu2+,Dy3+共掺样品发光性质的影响。结果表明,Eu2+,Dy3+共掺高硅氧发光玻璃中存在Dy3+向Eu2+的无辐射能量传递现象,且Dy3+的引入会使高硅氧发光玻璃中Eu—O的共价作用减弱,造成Eu2+发射峰蓝移;随着Dy3+浓度的增加,Dy3+→Eu2+能量传递增强,Eu2+发光增强;Dy3+含量继续增加,则Dy3+发光出现浓度猝灭,且Dy3+→Eu2+能量传递减弱。     

六方相LaOF纳米体系中Sm3+/Eu3+的能量转移效应

为了探讨Sm3+/Eu3+共掺体系的荧光光谱特性和能量转移机理,采用水热-烧结法制备了Sm3+/Eu3+共掺LaOF纳米晶体颗粒,并用X射线衍射和透射电子显微镜对纳米晶体颗粒进行了表征.结果显示,所制备的纳米晶体颗粒呈六方相,均匀性和分散性良好,平均粒径为70 nm左右.通过442 nm连续光激发,在六方相LaOF:Sm3+/Eu3+纳米体系中实现了Sm3+离子向Eu3+离子的能量转移,观测到了因能量转移效应而产生的Eu3+离子5D0能级的荧光发射谱线.光谱学研究发现,能量转移源于Sm3+离子4G5/2能级向Eu3+离子5D0能级的弛豫过程,并且随着受主离子Eu3+浓度的增加,能量转移效率也随之提高.     

Tb/Eu 共掺锌硼磷酸盐白光发光玻璃的制备及其发光性能

采用熔体冷却法,通过控制玻璃基质组成及稀土离子添加量,制备了Tb、Eu单掺和Tb/Eu共掺的锌硼磷酸盐低熔点发光玻璃。测试了样品的红外光谱、吸收光谱、激发与发射光谱和荧光寿命,并计算CIE色坐标,研究了材料的微观结构及发光性能。结果表明：样品中部分Eu³⁺被还原为Eu²⁺,在380 nm波长激发下,Tb/Eu共掺发光玻璃同时出现Eu³⁺红光、Tb³⁺绿光和Eu²⁺蓝光的特征发射。增加基体中B₂O₃含量能强化玻璃网络结构,并改变Eu²⁺/Eu³⁺比例。发射光谱和荧光寿命测试表明,共掺的发光玻璃中存在Eu²⁺→Eu³⁺,Eu²⁺→Tb³⁺和Tb³⁺→Eu³⁺的能量传递。改变Tb、Eu的掺杂浓度能够有效改变发光玻璃的发光强度和颜色,最终得到色坐标为（0.318 7,0.286 1）、色温6 480 K的发光玻璃。     

CaS·Cu+,Eu2+的光致发光及其在农业生产中的应用

研究了Cu+,Eu2+共激活的CaS的发光性质及激活剂浓度与荧光性质的关系.Cu+和Eu2+的发射光谱分别在430 nm附近及630 nm附近,它们是由Cu''Ca-Vs2+中心的离子发射和Eu2+的5d-4f跃迁发射产生的.实验结果表明,Cu+对Eu2+荧光发射有较强的敏化作用,Eu2+对Cu+发射峰值波长和强度也有显著影响;单掺Eu2+或Cu+的荧光粉是良好的农用薄膜红,蓝光转换剂,共掺Eu2+和Cu+的CaS荧光粉作光转换农膜添加剂可望人工模拟叶绿素的吸收光谱,使作物在植物最佳生长作用光谱环境中生长,促使作物早熟或提高作物产量.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.