Ultrafast carrier dynamics in GeSn thin film based on time-resolved terahertz spectroscopy

We measure the time-resolved terahertz spectroscopy of GeSn thin film and studied the ultrafast dynamics of its photo-generated carriers.The experimental results show that there are photo-generated carriers in GeSn under femtosecond laser excitation at 2500 nm,and its pump-induced photoconductivity can be explained by the Drude–Smith model.The carrier recombination process is mainly dominated by defect-assisted Auger processes and defect capture.The firstand second-order recombination rates are obtained by the rate equation fitting,which are(2.6±1.1)×10^(-2)ps^(-1)and(6.6±1.8)×10^(-19)cm^(3)·ps^(-1),respectively.Meanwhile,we also obtain the diffusion length of photo-generated carriers in GeSn,which is about 0.4μm,and it changes with the pump delay time.These results are important for the GeSn-based infrared optoelectronic devices,and demonstrate that Ge Sn materials can be applied to high-speed optoelectronic detectors and other applications.

Enhancing redshift phenomenon in time-resolved photoluminescence spectra of AlGaN epilayer

AlGaN epitaxial layer has been studied by means of temperature-dependent time-integrated photoluminescence（PL）and time-resolved photoluminescence（TRPL）. An enhancing redshift phenomenon in TRPL spectra with increasing temperature was observed, and the localized excitons behaved like quasi two-dimensional excitons between 6 K and 90 K. We demonstrated that these behaviors are caused by a change in the carrier dynamics with increasing temperature due to the competition of carriers＇ localization and delocalization in the AlGaN alloy.

Time-Resolved Photoluminescence Spectra of Porous Si

he photoluminescence spectra of porous Si have been studied. Its timere-solved luminescence spectra show a red shift of luminescencc peak with increasingdelay time after exciting and a nonexponential decay. Several spectral bands withdifferent Gaussian center appear by means of the decomposition of a spetrum. Theresuits of our experiments show quantum confined characters in porous Si, and wespeculate that the short wavelength band at 465 nm is the direct band froni P_(15) toP_(25)

Time-Resolved Photoluminescence Study of Silicon Nanoporous Pillar Array

A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence （PL） of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites （nc-Si）, oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si-O^i bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.

Detection of K in soil using time-resolved laser-induced breakdown spectroscopy based on convolutional neural networks

One of the technical bottlenecks of traditional laser-induced breakdown spectroscopy(LIBS) is the difficulty in quantitative detection caused by the matrix effect. To troubleshoot this problem,this paper investigated a combination of time-resolved LIBS and convolutional neural networks(CNNs) to improve K determination in soil. The time-resolved LIBS contained the information of both wavelength and time dimension. The spectra of wavelength dimension showed the characteristic emission lines of elements, and those of time dimension presented the plasma decay trend. The one-dimensional data of LIBS intensity from the emission line at 766.49 nm were extracted and correlated with the K concentration, showing a poor correlation of R_c^2?=?0.0967, which is caused by the matrix effect of heterogeneous soil. For the wavelength dimension, the two-dimensional data of traditional integrated LIBS were extracted and analyzed by an artificial neural network(ANN), showing R_v^2?=?0.6318 and the root mean square error of validation(RMSEV)?=?0.6234. For the time dimension, the two-dimensional data of time-decay LIBS were extracted and analyzed by ANN, showing R_v^2?=?0.7366 and RMSEV?=?0.7855.These higher determination coefficients reveal that both the non-K emission lines of wavelength dimension and the spectral decay of time dimension could assist in quantitative detection of K.However, due to limited calibration samples, the two-dimensional models presented over-fitting.The three-dimensional data of time-resolved LIBS were analyzed by CNNs, which extracted and integrated the information of both the wavelength and time dimension, showing the R_v^2?=?0.9968 and RMSEV?=?0.0785. CNN analysis of time-resolved LIBS is capable of improving the determination of K in soil.

Aqueous Sulfur Passivation of N-Type GaSb Substrates Studied by Photoluminescence Spectroscopy

In this work the influence of aqueous sulfur passivation on the surface of n-type (100) GaSb single crystals has been studied through low-temperature photoluminescence (PL) characterization. The samples were passivated at different times using aqueous solutions of sodium sulfide. PL spectroscopy was used to determinate the optimum time of sulfur passivation, through the measurement of the PL intensity for the different passivation times. For the samples measured, the PL spectra show the presence of two emission bands, whose intensity and energy position change for the different passivation times of the GaSb samples. According to the PL results, a passivation surface treatment of 6 min shows the highest PL intensity spectrum.

Time-resolved spectroscopy for 5s^('4)D_(7/2) state transitions undergoing electron–ion recombination in femtosecond laser-produced copper plasma

In the femtosecond laser-produced Cu-plasma, the transient transition dynamics that the excited state 5s4D7/2 via electron-ion recombination transfers to 4p4F9/20 （465.11 nm, Λ1 line） and 4p4D7/20 （529.25 nm, Λ2 line） states are investigated by using the time-resolved spectroscopy. The occupation number and relevant lifetime of the excited state 5s4D7/2, the temporal evolutions of spectral intensities for Λ1 line and Λ2 line emissions are demonstrated to be in direct proportion to the employed laser intensity, which reveals the transient features of transition dynamics clearly differing from that resulted in the traditional collision excitation. Furthermore, some unique characteristics for Λ1 and Λ2 transitions stemming from electron-ion recombination are examined in detail.

Time-resolved spectroscopy of collinear femtosecond and nanosecond dual-pulse laser-induced Cu plasmas

In this paper,we investigate the time-resolved spectroscopy of collinear femtosecond(fs)and nanosecond(ns)dual-pulse(DP)laser-induced plasmas.A copper target was used as an experimental sample,and the fs laser was considered as the time zero reference point.The interpulse delay between fs and ns laser beams was 3μs.First,we compared the time-resolved peak intensities of Cu(I)lines from Cu plasmas induced by fs+ns and ns+fs DP lasers with collinear configuration.The results showed that compared with the ns+fs DP,the fs+ns DP laser-induced Cu plasmas had stronger peak intensities and longer lifetimes.Second,we calculated time-resolved plasma temperatures using the Boltzmann plot with three spectral lines at Cu(I)510.55,515.32 and 521.82 nm.In addition,time-resolved electron densities were calculated based on Stark broadening with Cu(I)line at 521.82 nm.It was found that compared with ns+fs DP,the plasma temperatures and electron densities of the Cu plasmas induced by fs+ns DP laser were higher.Finally,we observed images of ablation craters under the two experimental conditions and found that the fs+ns DP laser-produced stronger ablation,which corresponded to stronger plasma emission.

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.

The interface of SiO_2/ZnS films studied by high resolution X-ray photoluminescence

Sharp interfaces in optoelectronic devices are key for proper band alignment. Despite its benefits as buffer layer, ZnS deposited via atomic layer deposition(ALD) renders intermixed interfaces to its substrate, which can be detrimental for device performance. Here, we are attempting to elucidate the chemical species deriving from this metal-oxide to metal-sulfide transition studying ultrathin film ZnS on SiO_2 using high resolution X-ray photoluminescence spectroscopy(XPS).Regarding the S 2p spectra after a deposition of only three cycles of ZnS, we discover the many different chemical species in which S is present. These include intermediate oxides such as SO_4^(2-).These species become more obvious as we tilt the sample in the XPS chamber to shallower angles.Comparing the Si 2p and S 2p high resolution peaks in the depth profile, one can clearly uncover the confinement of SO_4^(2-) to the interface of the underlying substrate. This may indicate that SiO_2/ZnS interfaces contain interfacial sulphates that likely alter the electronic configuration of this interface.

Confocal photoluminescence characterization of silicon-vacancy color centers in 4H-SiC fabricated by a femtosecond laser

Silicon-vacancy(VSi)centers in silicon carbide(SiC)are expected to serve as solid qubits,which can be used in quantum computing and sensing.As a new controllable color center fabrication method,femtosecond(fs)laserwriting has been gradually applied in the preparation of VSi in SiC.In this study,4H-SiCwas directlywritten by an fs laser and characterized at 293 K by atomic force microscopy,confocal photoluminescence(PL),and Raman spectroscopy.PL signals of VSi were found and analyzed using 785 nm laser excitation by means of depth profiling and two-dimensional mapping.The influence of machining parameters on the VSi formation was analyzed,and the three-dimensional distribution of VSi defects in the fs laser writing of 4H-SiC was established.

Diffusion effect on the decay of time-resolved photoluminescence under low illumination in lead halide perovskites

Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,instead of a single exponential one.This was considered to be a result of the surface and the bulk recombination or the additional radiative recombination caused by the high excited carrier density.Here,a new model considering the diffusion and the trap-assisted recombination of carriers is proposed to explain the TRPL curves.The expressions of the TRPL curves and the transient absorption(TA)dynamic curves are theoretically derived,demonstrating that the TRPL curve is an infinite exponential series,regardless of the presence of surface recombination or not.Our newly developed highly sensitive nanosecond TA and TRPL were employed to measure the carrier dynamics of the same sample under low illumination in the linear response region of TA,thereby experimentally verifying our model.These results suggest that the decay of the TRPL is not only a consequence of the carrier recombination but also the carrier diffusion.TRPL cannot provide a direct measurement of the carrier lifetime,whereas TA spectroscopy can.Furthermore,the surface and the bulk recombination can be resolved and the average diffusion coefficient(D)can also be correctly obtained by combining TRPL and TA measurements.We also propose an approximate method for calculating the carrier lifetime and diffusion coefficient of high-quality perovskite films.Our model provides not only a new interpretation of the dynamics of the PL decay but also a deep insight into the carrier dynamics in the nanosecond time scale under working condition of perovskites solar cells.

In_(0.52)Al_(0.48)As/InP的正向和反向异质结在带隙附近的不同光谱现象

应用光电导谱(PC)和光致发光谱(PL)研究了由分子束外延在InP(100)衬底上生长In_(0.52)Al_(0.48)As获得的两种异质结外延结构,分别是在InP衬底上生长InAlAs形成的正向异质结样品(样品A:In_(0.52)Al_(0.48)As/InP)和InAlAs层继续生长InP形成的上层为反向异质结的双异质结样品(样品B:InP/In_(0.52)Al_(0.48)As/InP).PL和PC实验采用光从表面入射激发的测量构型,样品测量温度为77 K.样品A的PC谱显示,在激发光能量大于表面In_(0.52)Al_(0.48)As层的带隙时出现了电导陡降的反常变化,还在916 nm波长处呈现一小的电导峰结构.PL谱对应此波长位置则出现很强的发光峰.样品B则未观察到上述光谱特征,该差异可从两类异质结不同的界面电子结构获得解释.

Transient Spectroscopic Properties of [60]Fullerene-Containing Cyclic Sulphoxide

The properties of the triplet excited state of [60]fullerene-containing cyclic sulphoxide have been investigated by time-resolved absorption spectroscopy. Transient absorption bands of [60]fullerene-containing cyclic sulphoxide showed two decay-components, which were attributed to triplet excited states of different spin multiplicity. The properties of photoexcited states of [60]fullerene-containing cyclic sulphoxide are also reported.

Influence of target temperature on femtosecond laser-ablated brass plasma spectroscopy

Spectral intensity,electron temperature and density of laser-induced plasma(LIP) are important parameters for affecting sensitivity of laser-induced breakdown spectroscopy(LIBS).Increasing target temperature is an easy and feasible method to improve the sensitivity.In this paper,a brass target in a temperature range from 25℃ to 200℃ was ablated to generate the LIP using femtosecond pulse.Time-resolved spectral emission of the femtosecond LIBS was measured under different target temperatures.The results showed that,compared with the experimental condition of 25℃,the spectral intensity of the femtosecond LIP was enhanced with more temperature target.In addition,the electron temperature and density were calculated by Boltzmann equation and Stark broadening,indicating that the changes in the electron temperature and density of femtosecond LIP with the increase of the target temperature were different from each other.By increasing the target temperature,the electron temperature increased while the electron density decreased.Therefore,in femtosecond LIBS,a hightemperature and low-density plasma with high emission can be generated by increasing the target temperature.The increase in the target temperature can improve the resolution and sensitivity of femtosecond LIBS.

Optical spectroscopy study of damage evolution in 6H-SiC by H_(2)^(+)implantation

Lattice defects induced by ion implantation into SiC have been widely investigated in the decades by various techniques.One of the non-destructive techniques suitable to study the lattice defects in SiC is the optical characterization.In this work,confocal Raman scattering spectroscopy and photoluminescence spectrum have been used to study the effects of 134-keV H_(2)^(+)implantation and thermal treatment in the microstructure of 6H-SiC single crystal.The radiation-induced changes in the microstructure were assessed by integrating Raman-scattering peaks intensity and considering the asymmetry of Raman-scattering peaks.The integrated intensities of Raman scattering spectroscopy and photoluminescence spectrum decrease with increasing the fluence.The recovery of the optical intensities depends on the combination of the implantation temperature and the annealing temperature with the thermal treatment from 700℃to 1100℃.The different characterizations of Raman scattering spectroscopy and photoluminescence spectrum are compared and discussed in this study.

多晶金刚石薄膜硅空位色心形成机理及调控

金刚石硅空位色心在量子信息技术和生物标记领域有重要应用前景.本文对硅衬底上多晶金刚石生长过程中硅空位色心形成机理及调控方法进行研究.通过改变金刚石生长氛围中的氮气和氧气比例,实现了对硅空位色心发光强度的有效调控,所制备系列多晶金刚石样品的光致发光光谱显示,硅空位色心荧光峰与金刚石本征峰的比值最低为1.48,最高可达334.46,该比值与金刚石晶粒尺寸正相关.进一步用光致发光面扫描和拉曼面扫描分析样品可知,多晶金刚石中的硅应来自于硅衬底,在多晶金刚石生长过程中,衬底硅单质先扩散至金刚石晶粒处,随着金刚石晶粒生长,硅单质再扩散并入金刚石晶体结构中形成硅空位色心.不同样品硅空位发光强度的差异,是由于生长过程中氮气和氧气对金刚石硅空位色心的形成分别起到促进和抑制的作用.

基于UV-Vis漫反射、Raman与PL光谱联用技术在黄色珍珠无损检测中的应用

应用紫外-可见(UV-Vis)漫反射、拉曼(Raman)与光致发光(PL)光谱就当前市售的大小各异、金色饱和度深浅不一的珍珠其致色属性予以对比分析。结果表明:基于珍珠UV-Vis漫反射光谱特征的差异将金黄色珍珠初分为两种类型:Ⅰ型珍珠其谱图在(360±5) nm处存在吸收带、在(420±10) nm处存在较弱的吸收峰或肩,该类珍珠为当前珍珠销售市场较为常见的自身致色珍珠;除Ⅰ型珍珠外,将其他金黄色系珍珠归属为Ⅱ型,其对应的UV-Vis反射光谱主吸收峰可位于340~430 nm区间,部分Ⅱ型样品在280~600 nm无明显吸收或仅存在较弱的吸收肩。进一步就Ⅱ型珍珠予以Raman光谱检测,在激发强度较低时经处理的Ⅱ型黄色珍珠在150~1 000 cm^(-1)区间可产生较强的荧光峰,且荧光峰的强度明显高于文石约1 086 cm^(-1)处的特征峰。同时,上述经处理的Ⅱ型珍珠对应的PL光谱同样表明在500~600 nm区间的荧光强度显著增大。此外,部分经处理的珍珠其Raman或PL光谱中可见与珍珠组成成分无关的特征峰位。上述珍珠的Raman与PL光谱中出现的异常荧光与外来特征峰可作为珍珠经处理的佐证依据。课题工作为当前金黄色珍珠颜色的形成属性及仿珍珠的鉴定提供理论与技术支撑,同时对于Raman光谱在其他类宝玉石、特别是有机宝石的检测鉴定中具有重要的借鉴意义。

On the origin of carrier localization in AlInAsSb digital alloy

We compared the photoluminescence(PL)properties of Al In As Sb digital alloy samples with different periods grown on Ga Sb(001)substrates by molecular beam epitaxy.Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states.There are two different mechanisms for the origin of the PL intensity quenching for the Al In As Sb digital alloy.The high-temperature activation energy E_(1)is positively correlated with the interface thickness,whereas the low-temperature activation energy E_(2)is negatively correlated with the interface thickness.A quantitative high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)study shows that the interface quality improves as the interface thickness increases.Our results confirm that E_(1)comes from carrier trapping at a state in the In Sb interface layer,while E_(2)originates from the exciton binding energy due to the roughness of the Al As interface layer.

Time-resolved luminescent nanoprobes based on lanthanide nucleotide self-assemblies for alkaline phosphatase detection

Currently,enzyme-responsive nanomaterials have shown great promise in prognosis or diagnosis of disease biomarker.However,the great obstacle for conventional enzyme-responsive nanomaterials frequently lies in autofluorescence interference,poor monodispersity,uncontrollable size and morphology,low optical stability,and biotoxicity,which fundamentally impede their practical application in biological systems.To overcome these deficiencies,we proposed a novel strategy for reliable and precise detection of an enzyme disease biomarker,alkaline phosphatase(ALP),through lanthanide(Ln^(3+))nucleotide nanoparticles(LNNPs)with extremely improved monodispersity and uniformity,which were achieved by the coordination self-assembly between ATP and Ln^(3+)inside micellar nanoreactor.Specifically,for ATP-Ce/Tb LNNPs,highly improved photoluminescence(PL)emission of Tb^(3+)can be achieved via efficient Ce^(3+)sensitization.We demonstrated that ALP could specifically cleave the phosphorus–oxygen(P–O)bonds of ATP and result in the collapse of ATP-Ce/Tb scaffold,finally leading to the PL quenching of Tb^(3+).By taking advantage of time-resolved(TR)PL technique,the fabricated ATP-Ce/Tb LNNPs presented superior selectivity and sensitivity for the ALP bioassay in complicated serum samples,thus revealing the great potential of ATP-Ce/Tb LNNPs in the areas of ALP-related disease prognosis and diagnosis.