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)

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 of anatase/rutile TiO_2 phase junction revealing charge separation dynamics

Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

Time-resolved characteristics of a nanosecond pulsed multi-hollow needle plate packed bed dielectric barrier discharge

In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and achieve large-volume stable discharge.The dynamic characteristics of the plasma,the generated active species,and the energy transfer mechanisms in both positive discharge(PD)and negative discharge(ND)are investigated by using fast-exposure intensified charge coupled device(ICCD)images and time-resolved optical emission spectra.The experimental results show that the discharge intensity,number of discharge channels,and discharge volume are obviously enhanced when the multi-needle electrode is replaced by a multihollow needle electrode.During a single voltage pulse period,PD mainly develops in a streamer mode,which results in a stronger discharge current,luminous intensity,and E/N compared with the diffuse mode observed in ND.In PD,as the gap between dielectric beads changes from 0 to250μm,the discharge between the dielectric bead gap changes from a partial discharge to a standing filamentary micro-discharge,which allows the plasma to leave the local area and is conducive to the propagation of surface streamers.In ND,the discharge only appears as a diffusionlike mode between the gap of dielectric beads,regardless of whether there is a discharge gap.Moreover,the generation of excited states N_(2)^(+)(B^(2)∑_(u)^(+))and N2(C^(3)Π_(u))is mainly observed in PD,which is attributed to the higher E/N in PD than that in ND.However,the generation of the OH(A^(2)∑^(+))radical in ND is higher than in PD.It is not directly dominated by E/N,but mainly by the resonant energy transfer process between metastable N_(2)(A^(3)∑_(u)^(+))and OH(X^(2)Π).Furthermore,both PD and ND demonstrate obvious energy relaxation processes of electron-to-vibration and vibration-to-vibration,and no vibration-to-rotation energy relaxation process is observed.

Time-resolved K-shell x-ray spectra of nanosecond laser-produced titanium tracer in gold plasmas

A study of a nanosecond laser irradiation on the titanium-layer-buried gold planar target is presented. The timeresolved x-ray emission spectra of titanium tracer are measured by a streaked crystal spectrometer. By comparing the simulated spectra obtained by using the FLYCHK code with the measured titanium spectra, the temporal plasma states, i.e.,the electron temperatures and densities, are deduced. To evaluate the feasibility of using the method for the characterization of Au plasma states, the deduced plasma states from the measured titanium spectra are compared with the Multi-1D hydrodynamic simulations of laser-produced Au plasmas. By comparing the measured and simulated results, an overall agreement for the electron temperatures is found, whereas there are deviations in the electron densities. The experiment–theory discrepancy may suggest that the plasma state could not be well reproduced by the Multi-1D hydrodynamic simulation, in which the radial gradient is not taken into account. Further investigations on the spectral characterization and hydrodynamic simulations of the plasma states are needed. All the measured and FLYCHK simulated spectra are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.57760/sciencedb.j00113.00032.

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.

Photoluminescence Spectra of Disordered and Ordered Ga_(0.52)In_(0.48)P

Temperature-dependence and excitation-intensity-dependence of photoluminescence spectra for both disordered and ordered Ga 0.52 In 0.48 P are measured. The disordered sample is characterized by its single peak photoluminescence spectrum which is excitation-intensity independent and has different activation energy at different temperature region. The ordered sample shows double peaks, the intensity of the high-energy peak has an anomalous increase firstly and quenches afterwards. The relative phenomena are reasonably explained in terms of lattice ordering and orientation superlattice model.

Time-resolved photoluminescence:a precision tool for shallow trap density determination in perovskite films

Determining the trap density in the absorbing layer thin film of perovskite solar cells is a critically important task,as it directly influences the efficiency of the devices.Here,we proposed time-resolved photoluminescence(TRPL)as a nondestructive method to assess trap density.A model was constructed to investigate carrier recombination and transition in perovskite materials.The model was utilized for numerical calculations and successfully fitted TRPL signals of perovskite materials.Furthermore,a genetic algorithm was employed to optimize the parameters.Finally,statistical methods were applied to obtain the parameters associated with the trap states of the material.This approach facilitates the successful determination of trap densities for different samples with clear differentiation.

The Photoluminescence Spectra of the Aeschynite Group Minerals

Raman and photoluminescence spectra of the metamict and annealing recrystallization titanoaeschynite-(Nd) and nioboaeschynite-(Ce), found in Baiyunobo mineral deposit in China, were measured and discussed. The peaks or bands in the spectra of the metamic minerals are weak, broad and diffuse, but sharpen notably after heating. The results show that the distortion of the structure and disorder state of the elements exists in the minerals when natural crystalline minerals transformed in-to metamict minerals after a long period of self-irradiation structure damaging. And all bands in the photoluminescence spectra of the aeschynite group mineral stem from emission transitions of Nd3+, when 514.5 nm laser is used as the excitation source.

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.

Photoluminescence of Por-Si with High-ordered Mosaic Structure Received at Long Anodic Etching p-Si (100) in the Electrolyte with an Internal Current Source

Photoluminescence spectra and nature of light-emitting centers of a porous silicon (por-Si) samples are given. The por- Si samples had high-ordered mosaic structure, which was received under long anodic etching p-Si(100) in electrolyte with an internal current source. The photoluminescence spectra were monitored at room temperature before and after annealing in air and vacuum. Comparative analysis of photoluminescence spectra of the por-Si samples annealed at different temperatures in air and vacuum shows that the thermal annealing conditions has significant effect on the intensity and spectral content of the photoluminescence spectra. The nature of the luminescence emission centers at different temperatures and annealing conditions was discussed.

Fabrication and photoluminescence characteristics of nonuniform Yb-Er codoped films

The nonuniform Yb-Er Codoped Al2O3 films were prepared on SiO2/Si substrates using a medium frequency magnetron sputtering system. Two asymmetry targets in the system were introduced to realize the nonuniform dopant. Some curves of Photoluminescence （PL） peak intensity were obtained by adjusting the deposition parameters, such as, the pillar number of erbium and ytterbium in the mixed target and the distance between a sample table and targets. Typically, the curve of PL peak intensity against the offset distance was approximately linear. The ratio of the PL intensity at the two ends of the same sample was 12.6 and the slope was 71.83/mm when the pillar numbers of the erbium and ytterbium in the mixed target are 5 and 60, respectively, and the distance between targets and the sample table is 2.9 cm.

Effect of different catalysts and growth temperature on the photoluminescence properties of zinc silicate nanostructures grown via vapor-liquid-solid method

We explore the photoluminescence properties of zinc silicate(Zn_(2)SiO_(4)) nanostructures synthesized by vapor-liquidsolid(VLS)mode of growth using three different catalysts(Sn,Ag,and Mn).Different catalysts significantly influence the growth rate which in turn has an impact on the structure and hence the photoluminescence of the prepared zinc silicate nanostructures.Zn_(2)SiO_(4) has a wide bandgap of about 5.5 eV and in its pure form,it does not emit in visible region due to its inner shell electronic transitions between the 3 d5 energy levels.However,the incorporation of different catalysts(Sn,Ag and Mn)at different growth temperatures into the Zn_(2)SiO_(4) crystal growth kinetics provides wide visible spectral range of photoluminescence(PL)emissions.PL analysis shows broad multi-band spectrum in the visible region and distinct colors(red,yellow,green,blue,cyan and violet)are obtained depending on the crystalline structure of the prepared nanostructures.The allowed transitions due to the effect of different catalysts on zinc silicate lattice offer a huge cross-section of absorption that generates strong photoluminescence.The correlation between the structural and optical properties of the synthesized nanostructures is discussed in detail.The synthesized photoluminescent nanostructures have potential applications in solidstate lighting and display devices.

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.

不同厚度WS_(2)光学性质

利用光学手段对蓝宝石衬底上生长的大面积单层、少层、块体WS_(2)的物理性质进行研究.首先利用原子力显微镜测量样品的厚度估算样品层数,并利用X线衍射测量样品的晶相判断其单晶特性.然后通过拉曼光谱和光致发光光谱技术研究样品的质量和光学特性,发现E_(2g)^(1)模和A 1g模明显且尖锐,说明晶格结构比较完整,2个模式随着层数增加发生频移;单层和多层WS_(2)的直接激子跃迁峰均存在不对称性,说明都存在电荷掺杂,其光致发光强度随着层数增加发生减弱.进一步通过测试变激发功率拉曼光谱和变激发功率光致发光光谱,发现少层、块体WS_(2)中的E_(2g)^(1)模随着激发功率的增加未发生频移,说明激光热效应可以忽略;少层、块体WS_(2)中的直接激子跃迁峰随激发功率的增加发生频移,说明存在载流子的相互作用;少层WS_(2)光致发光强度的变化幅度大于块体,这与层间相互作用强弱有关.

BaZnOS:Bi^(3+)荧光粉的制备及光学性能研究

以碳酸钡、硫化锌和氧化铋为原料,采用高温固相法合成了一系列铋(Bi)掺杂BaZnOS的蓝绿色荧光粉。研究了BaZnOS中Bi的位点占据、晶胞变化及其发光特性之间的相关性。在BaZnOS中,根据离子配位相同及半径相似原理,Ba位点是Bi最适合和稳定占据的位点。由于Bi^(3+)的半径略小于Ba^(2+)的半径,导致掺杂过后的晶胞参数有所缩小。在波长为372 nm的紫外光激发下,BaZnOS和BaZnOS:Bi^(3+)在400~600 nm处都显示出非常宽的发射带。其中未掺杂的BaZnOS发光归因于合成过程中的氧空位缺陷,掺杂Bi^(3+)后,Bi^(3+)结合到BaZnOS的晶格中,由于Bi^(3+)的^(3)P_(1,0)→^(1)S_(0)跃迁,最终使位于400~600 nm处的光致发光进一步增强2~3倍。通过色坐标计算,所制备的BaZnOS:Bi^(3+)荧光粉色坐标均位于蓝绿色区域,可作为与红光协调发射白光的潜力荧光粉,用于白光发光二极管领域。

Development and Application of Ultrafast Circular Dichroism Spectroscopy Techniques

Chirality hold broad applications in life sciences,quantum devices,and various other areas.Traditionally,molecular chirality can be characterized by using steady-state circular dichroism spectroscopy.However,the techniques that can characterize excited state chirality are progressively capturing the public interest as it can provide the dynamic information for chirality generation and transfer.In this review,we focus on the theoretical background and the developmental history of femtosecond time-resolved circular dichroism spectroscopy(TRCD)techniques around the world.Additionally,we provide examples to showcase the utility of these techniques in the analysis of the dynamical molecular chemical structures,the investigation of molecular chirality generation,and the detection of electron spin dynamics in semiconductor quantum dots.

激发波长为473nm的光致发光光谱特征对珍珠类型及其颜色成因的指示意义

通过激发波长为473 nm的光致发光光谱对不同颜色珍珠的光致发光特征进行了对比研究,结果表明:(1)颜色未经处理的灰色、黄色、紫色和橙色珍珠的光致发光光谱峰值在570~600 nm区间,与文石的峰值一致,推测其颜色主要与文石排列结构有关。(2)颜色未经处理的紫色和橙色珍珠在500~570 nm区间内出现与文石无关的发光峰,推测其颜色还同样受有机质的影响。(3)颜色未经处理黑珍珠的峰值在800~900 nm之间,推测其黑色调主要与有机质有关。(4)经染色处理珍珠的峰值主要位于650~750 nm区间内,主要与染剂有关,而不同颜色染色珍珠具有类似的发光特征说明染色珍珠所用染剂致色成分可能有相似的基团组成。相关研究成果可为珍珠的检测鉴定、颜色成因研究提供更多科学依据。

Mn^(2+)-activated calcium fluoride nanoprobes for time-resolved photoluminescence biosensing

Time-resolved (TR)photoluminescence (PL) technique has shown great promise in ultrasensitive biodetection and high-resolution bioimaging.Hitherto,almost all the TRPL bioprobes are based on the parity-forbidden f→f transition of lanthanide ions.Herein,we report TRPL biosensing by taking advantage of the d→d transition of transition metal (TM)Mn^2+ ion.We demonstrate that the Forster resonance energy transfer (FRET)signal can be distinguished from that of radiative reabsorption process through measuring the PL lifetime of Mn^2+,thus establishing a reliable method for Mn^2+ in homogeneous TR-FRET biodetection.We also demonstrate the biotin receptor-targeted cancer cell imaging by utilizing biotinylated CaF2:Ce,Mn nanoprobes.Furthermore,we show in a proof-of-concept experiment the appli- cation of the long-lived PL of Mn^2+ for TRPL bioimaging through the burst shot with a cell phone.These findings provide a general approach for exploiting the long-lived PL of TM ions for TRPL biosensing,thereby opening up a new avenue for the exploration of novel and versatile applications of TM ions.

Solvent and Temperature Effects on Spectral Properties of Two Poly(3-alkyl)thiophene Derivatives

Two alkyl substituted polythiophene derivatives: poly(3-hexylthiophene)(P3HT) and poly(3-decylthiophene)(P3DT), have synthesized by oxidation coupling polymerization of 3-alkylthiophene using iron(III) chloride as catalyst in chloroform. While both polymers in pure chloroform solution have maximum absorption at approximately same wavelength of 440nm, they behave differently with respect to changes observed on their UV-visible and photoluminescence spectra when the quality of the poor solvent is changed in good solvent (chloroform) / poor solvent (methanol) mixtures. With increasing volume fraction of methanol in mixtures, the absorption spectra of P3HT and P3DT red-shift, peaking at maximum wavelength of 495nm (P3HT) and 510nm(P3DT). Furthermore, the absorption spectra of the two polymers in chloroform blue-shift as the temperature rises. P3HT shows 4.73nm blue-shifts at 50℃ in contrast to the case at 20℃, while P3DT blue-shifts about 5.04nm. The photoluminescence spectra of the two polymers in mixed solution are also investigated, which show that the luminescence spectra shift to longer wavelength with an accompanying drop in the PL intensity as methanol is increased. The absorption and emission spectra of the two polymers in a poor solvent and a thin film are similar, which indicate that a similar longer conjugation length in the two cases. It could conclude that the polymers exist almost the same conformations and aggregations in both a poor solvent and a thin film. P3DT exhibits more sensitive spectra properties (big red-shifts in both absorption and luminescence spectra in poor solvents and large blue-shifts at high temperature) with contrast to P3HT, which imply that long side alkyl may improve the chromic properties of the polymer.