CdS/CdTe多晶薄膜的时间光谱特性

采用超短皮秒脉冲激光激发制备了SnO₂:F 玻璃衬底和石英衬底的CdTe多晶薄膜,在室温下测量其稳态和瞬态荧光光谱。结果表明,随着激发功率的增大,其荧光光谱峰逐渐展宽,并发生蓝移。对于退火处理的样品,其荧光光谱伴随主峰旁出现一个肩峰,是Cl 原子与富Cd区存在的空位形成复合体引起的发射。其瞬态荧光光谱寿命呈双指数衰减,即表面效应所引起的慢过程和带边激子态发射的快过程组成。样品退火处理后荧光寿命变长,有利于电子-空穴对在复合发光前分离,提高电子空穴的迁移率,改善其光伏性能。     

基于电荷转移过程的PAN-C60共聚物薄膜的时间分辨荧光研究

利用吸收光谱和皮秒时间分辨荧光研究PAN－C60星状共聚物的电荷转移过程。PAN－C60共聚物的吸收和荧光光谱结果显示共聚物中存在着电荷转移过程。时间分辨荧光结果表明PAN的荧光衰减遵循双指数衰减规律（一快过程160ps和一慢过程1500ps)，快衰减过程主要来源于聚合物中主链间相互作用产生的空间间接极化子对的影响，慢变过程主要来源于单重态激子的辐射跃迁弛豫。在共聚物中，C60分子的存在除导致PAN激发态寿命缩短外，还影响聚合物链间的相互作用，C60分子对PAN荧光猝 灭作用主要通过慢变过程影响的，而对PAN的空间极化子对的影响主要与其快衰减过程有关。     

高等植物外周捕光天线LHCⅡ中的超快光动力学过程

利用飞秒抽运探测技术及时间分辨荧光(TRPL)等光谱技术对高等植物LHCⅡ中的超快光动力学过程进行了研究。在其时间分辨荧光光谱中表现出了明显的各向异性特性。实验上观察了LHCⅡ中色素间的能量传递过程,由飞秒动力学发现,单体内Chlb到邻近的Chla之间的能量传递在200～300fs的时间尺度,Chla激子带间的能量弛豫发生在几百飞秒,不同单体Chla分子间能量分布过程在几个皮秒。而时间分辨荧光和飞秒动力学过程中上百皮秒的慢过程归属于不同聚集体间的能量平衡过程或分子构象变化。     

PPV衍生物／C60薄膜的时间分辨荧光光谱研究

用皮秒锁模Ｎｄ：ＹＡＧ激光器的倍频输出作为激发光，用同步扫描条纹相机系统对聚对苯乙炔ＰＰＶ的两种衍生物，Ｐｏｌｙ（２－ｍｅｔｈｏｘｙ－５－（４－ｂｕｔｅｎｙｌｏｘｙ）ｐｈｅｎｙｌｅｎｅ ｖｉｎｙｌｅｎｅ）（ＭＢＰＰＶ）和Ｐｏｌｙ（２－ｍｅｔｈｏｘｙ－５－（４－ｂｒｏｍｏ－ｂｕｏｘｙ）ｐｈｅｎｙｌｅｎｅ ｖｉｎｙｌｅｎｅ）ＭＢＢ－ＰＰＶ），与富勒烯Ｃ６０的组合薄膜进行时间分辨荧光测量。     

Surface luminescence in ZnO nanoparticles

Spectral and time-resolved photoluminescence (TRPL) measurements were performed on ZnO nanoparticles of different sizes (17-300 nm). Under a low photon energy excitation of 2.33 eV, the time-integrated PL spectra (TIPL) clearly exhibit broad emission in the range of 1.2-2.3 eV. Upon increase of the particle size, a red-shift in the PL peak position was observed. Gaussian analysis indicates that this red-shift corresponds to the increased relative magnitude of the Gaussian combination in the low energy region. In addition, TRPL demonstrates a clear relationship between the particle diameters and the PL decay times. The shortening of the PL lifetime could be explained by a surface states model.     

Size-dependent optical properties and carriers dynamics in CdSe/ZnS quantum dots

Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots （QDs） were investigated by two-colour femtosecond （fs） pump-probe （400/800 nm） and picosecond time-resolved photoluminescence （ps TRPL） experiments. Pump-probe measurement results show that there are two components for the excited carriers relaxation, the fast one with a time constant of several ps arises from the Auger-type recombination, which shows almost particle sizeindependence. The slow relaxation component with a time constant of several decades of ns can be clearly determined with ps TRPL spectroscopy in which the slow relaxation process shows strong particle size-dependence. The decay time constants increase from 21 to 34 ns with the decrease of particle size from 3.2 to 2.1 nm. The room-temperature decay lifetime is due to the thermal mixing of bright and dark excitons, and the size-dependence of slow relaxation process can be explained very well in terms of simple three-level model.     

基于分子束外延生长的1.05 eV InGaAsP的超快光学特性研究

利用分子束外延方法制备了应用于四结光伏电池的1.05 eV InGaAsP薄膜, 并对其超快光学特性进行了研究. 温度和激发功率有关的发光特性表明: InGaAsP材料以自由激子发光为主. 室温下InGaAsP材料的载流子发光弛豫时间达到10.4 ns, 且随激发功率增大而增大. 发光弛豫时间随温度升高呈现S形变化, 在低于50 K时随温度升高而增大, 在50–150 K之间时减小, 而温度高于150 K时再次增大. 基于载流子弛豫动力学, 分析并解释了温度及非辐射复合中心浓度对样品材料载流子发光弛豫时间S形变化的影响.     

TIME-RESOLVED PHOTOLUMINESCENCE OF SINTERED ZnO CERAMICS

The time-resolved photoluminescence (TRPL) of sintered ZnO ceramics was measured at low temperatures. A broad luminescence band was observed in the visible region. The TRPL experiment shows that photoluminescence decay behaviour can be depicted as t^-n(r). The decay rate n(r) and lifetime are wavelength dependent, and the former varies exponentially with wavelength. The power-lowering behaviour of the luminescence intensity indicates that the luminescence band originates from the recombination of donor-acceptor pairs.     

Temperature-dependent luminescence dynamics for ZnO thin films

The paper presents the photoluminescence investigation of zinc oxide thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz wafers. The films with different thickness (number of layers) were annealed at different temperatures after the preparation process. It was found that high quality, transparent ZnO thin films could be produced on quartz substrates at relatively low annealing temperature (450–550  $^{\circ }\mathrm{C}$ ). The dependence of the ZnO thin film quality was studied by X-ray diffraction and atomic force microscopy techniques. Optical properties were investigated by classic and time-resolved photoluminescence (TRPL) measurements. Photoluminescence spectra allowed us to estimate energy of the free excitons, bond excitons and their longitudinal optical (LO) phonon replicas as a function of the annealing temperature. An innovative TRPL technique let us precisely measure the decay time of the free- and bond excitons’ in the real time. TRPL measurements as a function of temperature reveal a biexponential decay behavior with typical free/bound exciton decay constants of 970/5310 ps for the as-grown sample and 1380/5980 ps after annealing process. Presented spectra confirm high structural and optical quality of investigated films. We proved that the thermal treatment improve both optical and structural quality and extend the photoluminescence’s lifetimes. The obtained experimental results are important for identification of exciton’s peaks and their LO phonon replicas for the investigated ZnO films.     

InGaAs/GaAs量子链的光学特性研究

研究了InGaAs/GaAs量子链的稳态和瞬态光谱特性,特别是载流子的动力学过程.实验发现荧光寿命有很强的探测能量依赖关系,荧光寿命随发光能量的增加而减小;实验还发现,当激发功率较小时,荧光寿命随激发功率增大而增大,当激发功率足够大时,荧光寿命趋于饱和.这些结果清楚地表明,在量子链结构中,参与发光的载流子之间存在明显的耦合和输运现象,进一步分析表明,这种输运主要是由于载流子沿量子链方向的耦合造成的.发光的偏振特性研究进一步证实了载流子沿量子链方向输运过程. 关键词： InGaAs/GaAs 量子点 量子链     

Optical properties of 1.3 μm room temperature emitting InAs quantum dots covered by In0.4Ga0.6As/GaAs hetero-capping layer

Room temperature 1.3 μm emitting InAs quantum dots (QDs) covered by an In_0.4Ga_0.6As/GaAs strain reducing layer (SRL) have been fabricated by solid source molecular beam epitaxy (SSMBE) using the Stranski–Krastanov growth mode. The sample used has been investigated by temperature and excitation power dependent photoluminescence (PL), photoluminescence excitation (PLE), and time resolved photoluminescence (TRPL) experiments. Three emission peaks are apparent in the low temperature PL spectrum. We have found, through PLE measurement, a single quantum dot ground state and the corresponding first excited state with relatively large energy spacing. This attribute has been confirmed by TRPL measurements which allow comparison of the dynamics of the ground state with that of the excited states. Optical transitions related to the InGaAs quantum well have been also identified. Over the whole temperature range, the PL intensity is found to exhibit an anomalous increase with increasing temperatures up to 100 K and then followed by a drop by three orders of magnitude. Carrier’s activation energy out of the quantum dots is found to be close to the energy difference between each two subsequent transition energies. PACS 68.65.Ac; 68.65.Hb; 78.67.Hc     

Exciton localization behaviour in different well width undoped GaN/Al0.07Ga0.93N nanostructures

We report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al_0.07Ga_0.93N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the “S-shape” dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.     

GaAs间隔层厚度对InAs/GaAs量子点分子光学性质的影响

采用光致荧光发射谱(PL)和时间分辨荧光发射谱(TRPL)研究了GaAs间隔层厚度对自组装生长的双层InAs/GaAs量子点分子光学性质的影响.首先,测量低温下改变激发强度的PL谱,底层量子点和顶层量子点的PL强度比值随激发强度发生变化,表明两层量子点之间的耦合作用和层间载流子的转移随着间隔层厚度变大而变弱.接着测量改变温度的PL谱,量子点荧光光谱峰值位置(Emax)、半峰全宽及积分强度随温度发生变化,表明GaAs间隔层厚度直接影响到量子点内载流子的动力学过程和量子点发光的热淬灭过程.最后,TRPL测量发现60mL比40mL间隔层厚度样品的载流子隧穿时间有明显延长.     

表面等离激元对氮化硅薄膜中Tb3+离子荧光寿命的影响

利用等离子增强化学气相沉积和离子注入方法,制备了铽掺杂的氮化硅薄膜,然后利用磁控溅射和热处理工艺在薄膜上沉积了不同颗粒尺寸的银薄膜来研究表面等离激元共振对铽离子荧光寿命的影响.实验结果表明氮化硅中Tb³⁺离子的光致荧光最强峰在547 nm,而银薄膜的存在会明显降低稀土离子Tb³⁺的荧光寿命,其寿命的改变是由于银薄膜的表面等离激元改变了电磁场的分布,从而影响了系统的局域光模密度(PMD),理论计算的结果也验证了这一点.     

Luminescence of a ZnO:Ga crystal upon excitation in vacuum UV region

The spectral-kinetic characteristics of a ZnO:Ga single crystal upon excitation in the vacuum UV region have been studied. At a temperature of 8 K, the exciton luminescence line peaking at 3.356 eV has an extremely small half-width (7.2 meV) and a short decay time (360 ps). In the visible range, a wide luminescence band peaking at ～2.1 eV with a long luminescence time at 8 K and a decay time in the nanosecond range at 300 K is observed. The luminescence excitation spectra of ZnO:Ga have been measured in the range of 4–12.5 eV.     

Carrier recombination kinetics in (3 1 1)A InGaAs sidewall quantum wires

We present a study of the optical properties and carrier dynamics in strained InGaAs sidewall quantum wires (QWR) on patterned GaAs (3 1 1)A substrates by means of picosecond time-resolved photoluminescence (PL). A pronounced dynamical red shift of the QWR-PL band when increasing the delay time after the pulse excitation is observed. In addition, time-resolved data show a significant shortening of the PL decay time from the wire at short delay and when high excitation power is used. The data are compared with theoretical predictions. The results, i.e. the dynamical red shift observed in the wire emission and the shortening of the PL decay with increasing the excitation density, are interpreted in terms of a dynamical screening effect of the piezoelectric field.     

Time-resolved photoluminescence of delta-doped AlGaAs/GaAs heterostructures

The photoluminescence (PL) at low temperature of three delta-doped AlGaAs/GaAs heterostructures is investigated under continuous and pulsed excitations. The PL under continuous excitations allows the identification of the trapping centres and probes the carrier's transfer to the GaAs channel. The time-resolved photoluminescence (TRPL) inquires about carrier dynamics and gives radiative lifetimes of different levels. The DX level shows two time constants of the intensity decay relating the splitting of the valence band under impurity strains which reduce the crystal symmetry. The two time constants evolve with temperature and exhibit an increase near T=50 K.     

Kinetics of Triplet-Triplet Annihilation in Organic Glasses

In the present paper, the results of the investigation of the decay kinetics of delayed luminescence of organic glasses are presented. A strong deviation of the decay of both phosphorescence and annihilation delayed fluorescence from the exponential law is observed. This effect is shown to be due to the relaxation process of electronic excitation energy in the system with large energetic disorder. At the same time, the presence of two time intervals in which the rate coefficient for triplet-triplet annihilation (TTA) reaction shows different dependence on time is observed. On a short time scale the classical behavior is observed, i.e., the reaction is well described by the second-order equation with a time-independent rate coefficient. At the limit of long times, we have strong dependence of rate coefficient on time, i.e., the electronic excitation energy transport is dispersive. It is shown that behavior observed for the rate coefficient for TTA reaction is due to the relaxation process (on short time scale) and the equilibrium energy migration (in long time limit).     

Observation of coherent precursors in pulsed mode-stirred reverberation fields

We report on measured statistics of pulsed radio-frequency fields inside a dynamic (mode-stirred) reverberant cavity. Unlike for time-harmonic excitation, the early transient received power during the buildup of energy is quasiperiodic with respect to the stir angle and exhibits unusually long correlations. These correlations decay at the same exponential rate as the increase of energy. By contrast, the probability distribution of the power reaches its asymptotic form in a more rapid but oscillatory manner.     

The kinetics of exciton photoluminescence in mercuric iodide

Time-resolved photoluminescence (TRPL) of red mercuric iodide single crystal is measured at low temperatures and its two-photon luminescence is measured at room temperature. Sharp near band-gap luminescence is observed around 530 nm and was ascribed to radiative annihilation of free and bound excitons; the phonon replica of exciton luminescence are found between 533 and 540 nm at low temperatures. TRPL experiment reveals that near band-gap luminescence comprises fast and slow decay components and shows the different relaxation processes between free and bound exciton annihilation. Luminescence of bound excitons steeply lowers with increasing temperature and disappears about 40 K. A luminescence tail band is observed around 540 nm that is ascribed to defects in the anion sublattice. The temporal behavior of the tail band is described by rate equations very well. A broad luminescent band appears at 630 nm. The decay curves suggest that the luminescence is ascribed to the radiative recombination of donor-acceptor pairs and there are two kinds of mechanisms to control the decay. At room temperature, a luminescent band appears at the band-gap region, which shows the band-gap at room temperature is about 2.125 eV.