纳米PIC—I／azaPIC—I混合分子聚集体光学非线性的Z—扫描研究

引入胶体ＳＰ５４，在室温下形成ＰＩＣ－Ｉ（１，１ｄｉｅｔｈｙ１－２，２－ｃｙａｎｎｉｎｅＰ－ｔｏｕｅｎｅｓｕｌ－ｆｏｎａｔｅ－Ｉｏｄｉｄｅ）／ａｚａＰＩＣ－Ｉ的Ｊ－聚集体，用Ｚ－扫描技术系统研究了室温下纳米ＰＩＣ－Ｉ／ａｚａＰＩＣ－Ｉ，有机分子聚集体三种配比下的三阶光学非线性，观测到随着延长变短，样品的三阶非线性极化率增大，我们分析和讨论了这种非线性增强的机制。     

有机纳米分子聚集体PIC-I的Raman光谱研究

本文从分子聚集体ＰＩＣ－Ｉ的吸收光谱可观测到Ｊ－带的红移和窄化,并可算出１３６８ｃｍ－１振模,以及本实验条件下聚集体单体数目为Ｎ≈３链长为３×０．３ｎｍ＝０．９ｎｍ。测量了ＰＩＣ－Ｉ聚集体的荧光光谱,将它与吸收光谱相比较可以看出,聚集体吸收带（５７２．５ｎｍ）和荧光发射带（５７２．５ｎｍ）是共振的。系统地研究了ＰＩＣ－Ｉ聚集体的喇曼光谱（１００～１８００ｃｍ－１）,验证了振动模 １３６８ｃｍ－１的存在。     

氮化碳薄膜的X射线光电子谱

用ＸＰＳ研究射频－直流等离子体增强化学气相沉积获得的氮化碳薄膜的化学结构。Ｃ１ｓ和Ｎ１ｓ芯能级电子谱分析表明：在ＣＮ膜中含有Ｎ－ｓｐ＾３和Ｎ－ｓｐ６２两类化学结构,在高含Ｎ膜中还含有少量的Ｎ－ｓｐ相,且代表Ｎ－ｓｐ＾３结构的原子 比为１．２８,接近４：３,证明此膜中存在类β－Ｃ３Ｎ４相。     

混合分子聚集体有机纳米材料中相干与非相干皮秒脉冲累积光子回波

用双调制(斩波器和驻波调制器)和外差检测累积光子回波技术,研究了PIC-I和azaPIC-I混合分子集体有机纳米材料中一维Frenkel激子的位相弛豫过程.观测到激子失相时间T2随azaPIC-I克分子数的增大从60ps变为224ps.这与在含能量陷阱的分子聚集体中激子失相时间T2随陷阱的增加而变短的现象刚好相反.并且对在脉宽为4ps和相于时间为1ps的相干脉冲和非相干脉冲的不同激发条件下的实验结果进行了分析和讨论.     

卤代烷第一电离能的变化规律研究

卤代烷ＲＸ的第一电离能Ｉｐ的变化规律可用如下方程表示：Ｉｐ（ｅＶ）＝３．３３８０＋０．７３４４Ｅｐ（Ｘ）＋２．７４２４「（１／αｘ）ｑｘ」－１．４０２ＰＥＩ其中,Ｅｐ（Ｘ）、αｘ分别为卤素原子最外层Ｐ电子的电离能和原子极化离,ｑｘ是卤代烷ＲＸ分子中卤原子Ｘ所带的部分电荷,ＰＥＩ是ＲＸ分子中烷基Ｒ的极化效应指数。华肜上式估算卤代烷的第一电离能与实验值符合的比较好。     

类钡离子Y^8＋b到U^30＋5s^2^1S0—5s5p^1,3PJ振子强度计算

应用屏蔽氢模型计算了Ｙ＾８＋ｂ到Ｕ＾３０＋５ｓ＾２＾１Ｓ０－５ｓ５ｐ＾１Ｐ１振子强度ｆｉｆ，借助混合角，导出５ｓ＾２＾１Ｓ０－５ｓ５ｐ＾３Ｐ１组合跃迁振子强度ｆｉｆ与ｆｉｆ关系，计算结果与ＭＣＤＦ－ＯＬ法相吻合。     

类钡离子Y_b~(8 )到U~(30 )5s~(21)S_0-5s5p~(1,3)P_J振子强度计算

应用屏蔽氢模型计算Ｙ８＋ｂ到Ｕ３０＋５ｓ２１Ｓ０－５ｓ５ｐ１Ｐ１振子强度ｆｉｆ，借助混合角，导出５ｓ２１Ｓ０－５ｓ５ｐ３Ｐ１组合跃迁振子强度ｆｉｆ与ｆｉｆ关系，计算结果与ＭＣＤＦ－ＯＬ法相吻合     

用泵浦-探测方法研究ZnCdSe量子阱/CdSe量子点复合结构中的激子衰减

用飞秒泵浦－探测方法测量了ＺｎＣｄｓｅ量子阱／ＺｎＳｅ／ＣｄＳｅ量子点复合结构样品的透射特性。样品中ＺｎＳｅ垒层厚度为 １５ｎｍ,泵浦一探测结果得到上升沿时间为 ３６７±６０ｆｓ,下降沿时间为１．３±０．２ｐｓ。获得ＺｎＣｄＳｅ量子阱中激子寿命约为１ｐｓ。     

Cs3Cu2I5晶体薄膜吸收谱的研究

本文测定了Ｃｓ３Ｃｕ２ Ｉ５ 晶体薄膜在室温及液氮温度下的吸收谱,并依此计算出该材料的激子参数,即激子束缚能ΔＥ（１）ｅｘ ＝ （０．５３±０．０７）ｅＶ,激子半径ａｅｘ ＝ ０．３２６ ｎｍ ,禁带宽度Ｅｇ ＝ （５．００±０．０７）ｅＶ。在谱分析的基础上,论证了Ｃｓ３Ｃｕ２Ｉ５ 的电子和激子激发定域在该晶体的ＣｕＩ亚晶格之中,同时,揭示了在低温下Ｃｓｘ Ｃｕ１－ ｘ Ｉ系列化合物的第一激子峰位置随其摩尔组分变化的规律。     

类镉离子5s^2 ^1S0→5s5p^1,3P1跃迁振子强度的计算

应用屏蔽氢模型计算类Ｃｄ离子５ｓ２１Ｓ０→５ｓ５ｐ１Ｐ１共振跃迁振子强度，引入ｊ－耦合中校正系数Ｋ和混合角θ导出５ｓ２１Ｓ０→５ｓ５ｐ３Ｐ１跃迁振子强度表达式。计算结果和其他作者进行了比较，并给出某些讨论。     

Recombination dynamics of free and bound excitons in bulk GaN

We report new data on the transient photoluminescence behaviour of free and donor bound excitons in high quality bulk GaN material grown by HVPE. With 266 nm photoexcitation the no-phonon free exciton has a short decay time, about 100 ps at 2 K, assigned to nonradiative surface recombination. The LO replicas of the free exciton have a much longer decay at 2 K, about 1.4 ns, believed to be a lower bound for the bulk radiative lifetimes of the free excitons at 2 K. The donor bound exciton no-phonon lines exhibit a rather short (about 300 ps) nonexponential decay at 2 K, which appears to be dominated by a scattering process. The corresponding LO replicas and the two-electron transitions have a much longer decay. From the latter, the lower bound of the radiative lifetime of the O- and Si-bound excitons are 1800 ps and 1100 ps, respectively.     

Radiative recombination of free excitons in GaAs quantum wells

We have measured the radiative lifetime of excitons in GaAs quantum wells under resonant excitation at 10 K using time resolved luminescence spectroscopy with 6 ps time resolution. The luminescence decay has two components: a fast one with a time constant τ₁ (∼ 17 - 40 ps) and a slow one with a time constant τ₂ (∼ 80 - 300 ps). τ₂ is the lifetime of thermalised excitens at 10 K. τ₁ is due to two mechanisms in parallel: the radiative recombination of excitons with k_u < K₀ and the scattering by acoustical phonens into non radiative exciton states (k_u > k₀ and J = 2). The variation with temperature of τ₁ gives the lifetime of the excitons at k = 0, τ₀, which varies between 20 and 50 ps depending on the sample.     

Magnetooptics and dynamics of a magnetic polaron in semimagnetic CdSe/ZnMnSe quantum dots

The magnetooptics and picosecond dynamics of the radiative recombination of excitons in self-assembled semimagnetic CdSe/ZnMnSe quantum dots is studied at low temperatures. The behavior of individual quantum dots in a magnetic field and with an increase in temperature is indicative of a strong exchange interaction of excitons and magnetic Mn ions giving rise to a quasi-zero-dimensional exciton magnetic polaron. When the exciton energy exceeds the intracenter transition energy in Mn, the energy is rapidly transferred from excitons to Mn ions (faster than 20 ps). In the opposite case, a substantial red shift (～15 meV) of the emission line maximum is observed during the exciton lifetime ～500 ps, presenting the dynamics of the formation of a magnetic polaron with a characteristic time of ～110 ps.     

偏置电场对聚对苯乙烯激发态弛豫特性的影响

为探讨洞悉电场对有机发光二极管电致荧光量子效率的影响,通过激发-探测超快光谱技术研究了激子在电场下的瞬态行为.与单重态激子相应的激发态在230 μJ/cm2激发强度下,显示了快慢两个弛豫过程. 快慢组分的权重因子及快组分弛豫时间常数是电场相关的, 在6.4×10⁵ V/cm的电场下,与无偏置电场相比,激子的快组分弛豫时间加速,快组分的权重因子由22%增加为72%,约50%的初始激子又通过电场而离解. 慢组分是电场无关的,其弛豫时间常数为890 ps. 实验结果还揭示了由激发光所产生的长程声学声子,其声速为17 /ps. 关键词： 聚对苯乙烯 超快光谱 激子 有机发光二极管     

Ultrafast optical response in polydiacetylenes and polythiophenes

Ultrafast optical response in the films of poly(3-dodecylthiophene) (P3DT) and blue-and red-phase polydiacetylenes (PDA-4BCMU) has been investigated by femtosecond absorption and picosecond luminescence spectroscopies. Several nonlinear optical processes, i.e., hole burning, Raman gain, inverse Raman scattering, and induced-frequency shift, have been observed. The relaxation processes from photoexcited free excitons to self-trapped excitons (STEs) has been observed. The time constant is estimated as 140±40 fs in the blue-phase PDA-4BCMU and 100±50 fs in P3DT. The generated unthermalized STEs thermalize with the time constant of about 1 ps. The STEs in the blue-phase PDA-4BCMU decay exponentially with lifetime of 1.6±0.1 ps at 290 K and 2.1±0.2 ps at 10 K. The decay curves in the red-phase PDA-4BCMU and P3DT are not single exponential but can be fitted to biexponential functions with time constants of slightly shorter than 1 ps and about 5 ps. These two decay time constants correspond to relaxations to the ground state, respectively, from the free exciton and unthermalized STE and from the thermalized STE.     

Collective properties of excitons in the presence of a two-dimensional electron gas

We have studied the collective properties of two-dimensional (2D) excitons immersed within a quantum well which contains 2D excitons and a two-dimensional electron gas (2DEG). We have also analyzed the excitations for a system of 2D dipole excitons with spatially separated electrons and holes in a pair of quantum wells (CQWs) when one of the wells contains a 2DEG. Calculations of the superfluid density and the Kosterlitz–Thouless (K–T) phase transition temperature for the 2DEG-exciton system in a quantum well have shown that the K–T transition temperature increase with increasing exciton density and that it might be possible to have fast long-range transport of excitons. The superfluid density and the K–T transition temperature for dipole excitons in CQWs in the presence of a 2DEG in one of the wells increases with increasing inter-well separation.     

Picosecond excitonic luminescence in ZnO and other wide-gap semiconductors

Radiative lifetimes of free-atom transitions, scaled by ω³ for comparison at 368 nm, are not faster than about 6.9 ns. BaF₂ core-valence luminescence, scaled in the same way from 220 to 368 nm, corresponds to 4.1 ns. In contrast, excitonic transitions in wide-gap semiconductors display subnanosecond radiative lifetimes, and in particular ZnO has radiative lifetimes measured at 50–300 ps for D^o,X and 400–900 ps for free excitons. The “giant oscillator strength” corresponding to these lifetimes can be explained by theories developed initially for defect-bound excitons, then quantum wells, and nanoparticles. An exciton is a coherent array of N dipoles, where N is the number of sites covered by coherent translational motion of the exciton. This is not essentially a phenomenon of multiple excitons, but applies as well to single-exciton decay. It differs in that regard from the more familiar Dicke giant dipole of N coherently excited atoms lacking translational periodicity. The phenomenon suggests possibilities for achieving ultrafast scintillators and high light yield.     

Phonon and electronic nonradiative decay mechanisms of excitons in carbon nanotubes

We investigate theoretically the rates of nonradiative decay of excited semiconducting nanotubes by a variety of decay mechanisms and compare them with experimental findings. We find that the multiphonon decay (MPD) of free excitons is too slow to be responsible for the experimentally observed lifetimes. However, MPD lifetimes of localized excitons could be 2-3 orders of magnitude shorter. We also propose a new decay mechanism that relies on a finite doping of nanotubes and involves exciton decay into an optical phonon and an intraband electron-hole pair. The resulting lifetime is in the range of 5 to 100 ps, even for a moderate doping level.     

用Z扫描方法测量掺C60有机改良介质的非线性折射率

用Ｚ扫描方法和波长１．０６４μｍ、脉宽１５０ｐｓ的锁模激光测定了Ｃ６０／ＮＨ２－（ＣＨ２）３－Ｓｉ（ＯＣ２Ｈ５）３（简称Ｃ６０／ＫＨ５５０）溶胶和凝胶的三阶光学非线性系数。理论拟合曲线计算得出，溶胶复合材料的非线性折射率ｎ２＝５．６×１０－１２ｅｓｕ，经两天凝结之后的凝胶复合材料的ｎ２＝６．２×１０－１２ｅｓｕ。在相同的激光强度下溶胶和凝胶的不同透过率归因于溶胶液体对激光的非线性散射。