Preparation of ultrawide ZnSe nanoribbons with the function of lasing cavity

Ultrawide ZnSe nanoribbons are synthesized by the simple thermal evaporation. The microstructure of ZnSe nanoribbons is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), photoluminescence (PL) and Raman spectrum. It is found that the strong emission near the band gap of ZnSe centered at 460 nm is obtained in these nanoribbons. More importantly, ZnSe nanoribbons can act as lasing emitting optical cavities. Raman studies indicate that the longitudinal optic (LO) and transverse optic (TO) phonon confinements of the ZnSe nanoribbons shift to lower frequency.     

Bis-(8-hydroxyquinoline) mercury nanoribbons: preparation, characterization and photoconductivity

Bis-(8-hydroxyquinoline) mercury nanoribbons with average width of 300nm, thickness of 50nm and length of up to tens of micrometers were synthesized by a facile solvothermal method. X-ray powder diffraction and Fourier transform infrared spectrum were employed to determine their structure. The conductivity of a bundle of nanoribbons was also measured, which exhibited linear current-voltage characteristics and excellent photoresponse to light, indicating their potential applications in photoswitch nano-devices in the future.     

Bis-(8-hydroxyquinoline) copper nanoribbons: preparation, characterization, and photoconductivity

Bis-(8-hydroxyquinoline) copper nanoribbons with an average width of 400 nm, a thickness of 70 nm and the length of up to tens of micrometers, were synthesized by a facile solvothermal method. X-ray powder diffraction and Fourier transform infrared spectrum were employed to determine their structure. The photoconductivity of a bundle of nanoribbons was also measured, which exhibited unique photoresponse to light, indicating their potential applications in photoswitch nanodevices in the furure.     

Facile solvothermal synthesis and photoconductivity of one-dimensional organic Cd(Ⅱ)-Schiff-base nanoribbons

One-dimensional (1D) organic nanoribbons built on N-p-nitrophenylsalicylaldimine cadmium complex were synthesized via a facile solvothermal route. Scanning electron microscope images revealed that the as-synthesized products were ribbon like with widths of 500 nm,thicknesses of about 50nm, and lengthes up to several hundred micrometers. Fourier transform infrared spectrum was employed to characterize the structure. The conductivity of a bundle of nanoribbons was also measured,which showed that Schiff base cadmium nanoribbons had good photoconductive property. This work might enrich organic photoconductive materials and be applicable in nano photoswitch devices in the future.     

RT lasing via nanoscale CdSe islands in a (Zn,Mg)(S,Se) matrix

New approach for high performance lasing in semiconductors using an effect of exciton-induced waveguiding is proposed and realized. We demonstrate RT lasing in a structure without external waveguide formed by cladding of an active region with wider bandgap layers. Stacked arrays of nanoscale CdSe islands inserted directly in a wide bandgap matrix are used as an active media in our case. The lasing wavelength is 460 nm (2.69 eV) at 300K while the bandgap of the matrix material is 2.86 eV, providing an ultimate shift toward blue spectral range for the same matrix material.     

Measuring the optical properties of a trapped ZnO tetrapod

We report the onset of lasing from an electrodynamically trapped ZnO tetrapod. Each of the four legs of such an isolated tetrapod behaves as a single nanowire, where light is guided along the length of the wire and the necessary resonant feedback for lasing is provided at the two end facets. A diluted solution of ZnO tetrapods in methanol was sprayed in the form of a charged mist into a chamber containing the electrodynamic endcap trap. The quick evaporation of methanol assisted in trapping a single charged ZnO tetrapod. The trapped tetrapod is optically pumped with pulses from a Q-switched laser at a wavelength of 355 nm and emits light at 390 nm. For increasing pump fluences above 15 mJ/cm², a superlinear increase in intensity and a narrowing in the spectral width of the photoluminescence were observed, indicating lasing.     

Photoresponse Properties of CdSe Single‐Nanoribbon Photodetectors

Photodetectors are fabricated from individual single‐crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut‐off at 710 nm, corresponding to the bandgap of CdSe. The device exhibits a high photo‐to‐dark current ratio of five orders of magnitude at 650 nm, and can function with excellent stability, reproducibility, and high response speed (< 1 ms) in a wide range of switching frequency (up to 300 Hz). The photocurrent of the device shows a power‐law dependence on light intensity. This finding together with the analysis of the light intensity‐dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO₂ isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface.     

LD条宽对激射波长影响的研究

报道了LD激射波长会随条宽发生明显变化.对有相同外延生长结构和制作工艺、不同条宽的960 nm LD的激射波长进行研究发现,条宽为130、100、75和50 μm的器件的激射波长依次变短.进一步分析认为,这是因为条宽变窄导致器件阈值电流密度、阈值载流子密度变大造成的.根据GaAs材料在不同注入载流子密度下的增益谱及器件条宽变化对阈值载流子密度的影响,可以对实验现象进行合理的解释,从而在器件研制中可通过改变条宽对器件的激射波长在一定范围内进行调节.     

Lasing Behavior of BMPPV:PVK Mixture in Microcavity

The surface emitting microcavity is formed by sandwiching a polymer film containing poly (para-phenylene vinylene) (BMPPV) and poly (N-vinylcarbazole)(PVK) between a DBR with a reflectivity of 99.5% and a silver film.The sample is optically pumped by a 337.1 nm line of nitrogen laser with 10 ns pulses at 20 Hz repetition rate.The lasing phenomenon is observed in BMPPV and PVK mixture microcavity .The full width at half maximum( FWHM) is 6 nm at the peak wavelength of 460 nm.The lasing threshold energy is estimated to be about 5μJ.     

Influence of inhomogeneous broadening and deliberately introduced disorder on the width of the lasing spectrum of a quantum dot laser

Analytical expressions for the shape and width of the lasing spectra of a quantum-dot (QD) laser in the case of a small (in comparison with the spectrum width) homogeneous broadening of the QD energy levels have been obtained. It is shown that the dependence of the lasing spectrum width on the output power at room temperature is determined by two dimensionless parameters: the width of QD distribution over the optical-transition energy, normalized to temperature, and the ratio of the optical loss to the maximum gain. The optimal dimensions of the laser active region have been found to obtain a specified width of the emission spectrum at a minimum pump current. The possibility of using multilayer structures with QDs to increase the lasing spectrum’s width has been analyzed. It is shown that the use of several arrays of QDs with deliberately variable optical-transition energies leads to broadening of the lasing spectra; some numerical estimates are presented.     

Electrically pumped lasing from CdSe quantum dots

Fabrication of a ZnSe-based laser diode which employs a fivefold CdSe quantum dot stack separated by ZnSSe spacer layers of high S content is reported. For the first time, electrically pumped room-temperature lasing from such quantum dots was obtained at a wavelength around 560.5 nm. The threshold current density is 7.5 kA/cm ²     

808nm InGaAlAs垂直腔面发射激光器的结构设计

为实现垂直腔面发射半导体激光器(VCSEL)在808 nm波长的激射,对VCSEL芯片的整体结构进行了设计。基于应变量子阱的能带理论、固体模型理论、克龙尼克-潘纳模型和光学传输矩阵方法,计算了压应变InGaAlAs量子阱的带隙、带阶、量子化子能级以及分布布拉格反射镜(DBR)的反射谱,从而确定了量子阱的组分、厚度以及反射镜的对数。数值模拟的结果表明,阱宽为6 nm的In0.14Ga0.74Al0.12As/Al0.3Ga0.7As量子阱,在室温下激射波长在800 nm左右,其峰值材料增益在工作温度下达到4000 cm-1;渐变层为20 nm的Al0.9Ga0.1As/Al0.2Ga0.8As DBR,出光p面为23对时反射率为99.57%,全反射n面为39.5对时反射率为99.94%。设计的顶发射VCSEL结构通过光电集成专业软件(PICS3D)验证,得到室温下的光谱中心波长在800 nm处,证实了结构设计的正确性。     

一种新型有机染料HEASPS的激光上转换和光限幅性能

报道了一种新型上转换染料———反式 4 [4’ (N 羟乙基 N 乙基胺基 )苯乙烯基 ] N 甲基吡啶 对甲苯磺酸盐(trans 4 [4’ (N hydroxyethyl N ethylamino)styryl] N methylpyridiniump toluenesulfonate ,简称HEASPS)DMF溶液的激光上转换性质和光限幅性质。用Z 扫描技术测得其双光子吸收截面为σ2 =4.7× 10 -4 8cm4 ·s/photon ,研究了它在DMF溶剂中的线性吸收、单光子荧光、双光子荧光和双光子激射特性 ,用再吸收效应解释了双光子荧光峰相对单光子荧光峰的红移现象 ,该染料的激射和再吸收现象相互竞争导致了双光子激射峰相对于双光子荧光峰的蓝移现象。在 10 6 4nm皮秒脉冲激光的激发下 ,可得强烈的 6 2 6nm上转换激射光 ,上转换效率最高为 15 .5 % ,从抽运光到激射光的净转换效率为 2 6 %。该染料的DMF溶液表现出明显的光限幅特性     

Lasing in Cd(Zn)Se/ZnMgSSe heterostructures pumped by nitrogen and InGaN/GaN lasers

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm², a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T ₀=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.     

Random lasing in vertical ZnO nanorods

Random lasing with coherent feedback is detected in the array of vertical ZnO nanorods synthesized on a Si(100) substrate. Under high-intensity optical pumping at the wavelength of 337.1 nm at room temperature, several narrow laser peaks with the width of 0.1 nm are observed in the wavelength region around 392 nm. The laser radiation is emitted in a direction orthogonal to the axis of the nanorods. Study of the behavior of the laser spectrum with the excited area shows good agreement of the data with the theory of random lasers. The mechanism of laser emission is related to the formation of closed paths of light due to multiple coherent scattering at the vertically oriented ZnO nanorods.     

切换式双波长激发在掺镱和铒镱共掺复合式光纤激光器中的实现

抽运旁通腔型的掺镱光纤(YDF)激光器内剩余的抽运光功率随着入射抽运功率的变化呈现出光学双稳特性,这导致了用它来抽运另一个分叉腔的铒镱共掺光纤(EYDF)增益介质可获得第二个信号波长激发的可能性。根据这一原理,从实验上获得了1040 nm和1537 nm两个激发线的可切换振荡,这表明基于掺镱光纤激光器光学双稳态的复合腔结构(掺镱光纤激光器的抽运旁通腔和铒镱共掺光纤分叉腔)是实现切换式双波长光纤激光器光源的一个简单有效的方法。     

倾斜结构InGaAsP/InP集成超辐射光源

为提高半导体超辐射器件的输出功率 ,在原有的将超辐射发光管 (SLD)与半导体光放大器 (SOA)单片集成的基础上 ,将器件电流注入区中心轴线倾斜 6° ,制得了 1 5 μm倾斜结构的InGaAsP InP集成超辐射光源。发现这种新型结构的单片集成器件具有抑制激射的功能。在较低的电流注入下 ,得到了 38mW的脉冲超辐射输出功率。其光谱宽度 (FWHM )和平行、垂直于结平面的远场半宽分别为 16nm ,15°和 6 4°。同时 ,通过对该集成器件特性的研究 ,发现如何增加SOA部分的入射光功率是提高该集成器件性能的一个十分关键的因素     

Continuously Tunable Emission in Inverted Type‐I CdS/CdSe Core/Crown Semiconductor Nanoplatelets

The synthesis and unique tunable optical properties of core/crown nanoplatelets having an inverted Type‐I heterostructure are presented. Here, colloidal 2D CdS/CdSe heteronanoplatelets are grown with thickness of four monolayers using seed‐mediated method. In this work, it is shown that the emission peak of the resulting CdS/CdSe heteronanoplatelets can be continuously spectrally tuned between the peak emission wavelengths of the core only CdS nanoplatelets (421 nm) and CdSe nanoplatelets (515 nm) having the same vertical thickness. In these inverted Type‐I nanoplatelets, the unique continuous tunable emission is enabled by adjusting the lateral width of the CdSe crown, having a narrower bandgap, around the core CdS nanoplatelet, having a wider bandgap, as a result of the controlled lateral quantum confinement in the crown region additional to the pure vertical confinement. As a proof‐of‐concept demonstration, a white light generation is shown by using color conversion with these CdS/CdSe heteronanoplatelets having finely tuned thin crowns, resulting in a color rendering index of 80. The robust control of the electronic structure in such inverted Type‐I heteronanoplatelets achieved by tailoring the lateral extent of the crown coating around the core template presents a new enabling pathway for bandgap engineering in solution‐processed quantum wells.     

基于量子棒纳米纤维大面积定向排列的偏振增亮膜及其在宽色域显示中的应用

作为一种新兴的纳米材料,CdSe/CdS量子棒的偏振发光特性使其在应用于新型液晶显示中极具潜力,而如何将量子棒材料在宏观尺度上大面积的定向排列是实现该技术的关键性问题。在本文中,我们报道了一种大面积、含定向排列量子棒、基于PMMA纳米纤维制成的偏振增亮膜。首先,采用一种新的TBP辅助合成方法,合成出具有核壳结构的CdSe/CdS量子棒。该材料的绝对量子产率达到了60%,发光波长的半峰宽为25nm,具有182nm的大Stokes位移。随后将这些量子棒溶于氯仿、DMF和PMMA混合溶液中制备用于静电纺丝的纺丝液。通过静电纺丝技术,将含有量子棒的聚合物纳米纤维通过滚筒收集处理,得到了一张透明、大面积、偏振增强的增亮膜,5cm~2增亮膜的偏振度为0.45。最后将制备的增亮膜嵌入一个液晶显示模组中测试,结果显示该模组的亮度提高了18.4%。这一结果表明我们制备的量子棒增亮膜在新型宽色域高光效显示领域具有非常广阔的应用前景。     

测量激光器结温的脉冲注入法研究

提出了一种精确测量半导体激光器结温的方法。由于激光器的热容很小，因此采用脉冲注入的方法可以显著减小激光器的温升。研究了脉冲电流注入下激光器的激射波长随环境温度的变化规律，通过实验研究得到电流脉冲宽度和周期与激射波长的关系，理论分析得到的定量关系式与实验结果十分吻合。在此基础上得到了精确测量激光器结温的最佳脉冲参数。即脉宽为10ns，脉冲周期为10μs。并且确定了激光器结温与激射波长的定量关系式，波长随温度的漂移系数为0．0728nm／K。这种方法避免了电学测量法中的结电压波形过冲。测量精度明显优于后者，同时也可以方便地测量封装好的激光器组件的温度特性。