Cloning of rainbow trout (Oncorhynchus mykiss) histone H3 promoter and the activity analysis in rare minnow (Gobiocypris rarus)

Rainbow trout historic H3 (RH3) promoter was cloned via high fidelity PCR. The cloned RH3 promoter was inserted into a promoter-lacked vector pEGFP-1, resulting in an expression vector pRH3FGFP-1. The linearized pRH3EGFP-1 was microinjected into fertilized eggs of rare minnows and the sequential embryogenetic processes were monitored under a fluorescent microscope. Strong green fluorescence was ubiquitously observed at as early as the gastrula stage and then in various tissues at the fry stage. The results indicate that RH3 promoter, as a piscine promoter, could serve in producing transgenic Cyprinoid such as rare minnow. Promoter activity of RH3, CMV and common carp beta-actin (CA) were compared in rare minnow by the expression of respective recombinant EGFP vectors. The expression of pCMVEGFP occurred earlier than the following one, pRH3EGFP-1, and then pCAEGFP during the embryogenesis of the transgenics. Their expression activities demonstrated that the CMV promoter is the strongest one, followed by the CA and then the RH3.

RecA-mediated, targeted mutagenesis in zebrafish

We have evaluated the efficacy of RecA, a prokaryotic protein involved with homologous recombination, to direct site-specific mutagenesis in zebrafish embryos. For this we coinjected a vector containing a mutated enhanced green fluorescent protein (EGFP) gene plus 236-nucleotide corrective single-stranded DNAs coated with RecA into I-cell zebrafish embryos. Twenty-hours after fertilization, about 5% to 20% of injected embryos showed EGFP expression in I or more cells when RecA-coated corrective DNAs were used, but not when RecA was omitted. Mutated EGFP genes with 1-bp insertions or deletions were inefficiently activated, whereas those with 7-bp insertions were activated about 4-fold more efficiently. RecA-coated template strand had a higher efficiency than its complementary strand in activation of EGFP expression. Prior irradiation of the embryos with UV light enhanced RecA-mediated restoration of gene activity, suggesting that the effects we observed were augmented by one or more factors of zebrafish DNA repair systems.

Time course of foreign gene integration and expression in transgenic fish embryos

Using a nuclear transplantation approach, the integration and expression of the green fluorescent protein (GFP) gene in the embryogenesis of transgenic leach (Misgurnus anguillicaudatus Cantor) have been studied. The GFP gene expression is first observed at the gastrula stage, which is consistent with the initiation of cell differentiation of fish embryos. The time course of the foreign gene expression is correlated with the regulatory sequences. The expression efficiency also depends on the gene configuration: the expression of pre-integrating circular plasmid at early embryos is higher than that of the linear plasmid. The integration of the GFP gene is first detected at the blastula stage and lasts for quite a long period. When two types of different plasmids are co-injected into fertilized eggs, the behavior of their integration and expression is not identical.

Investigation of gain recovery for InAs/GaAs quantum dot semiconductor optical amplifiers by rate equation simulation

The gain recoveries in quantum dot semiconductor optical amplifiers (QD SOAs) are numerically studied by rate equation simulation. Similar to the optical pump-probe experiment, the injection of double 150 fs optical pulses is used to simulate the gain recovery of a weak continuous signal under different injection levels, inhomogeneous broadenings, detuning wavelengths, and pulse signal energies for the QD SOAs. The obtained gain recoveries are then fitted by a response function with multiple exponential terms to determine the response times. The gain recovery can be described by three exponential terms with the time constants, which can be explained as carrier relaxation from the excited state to the ground state, carrier captured by the excited state from the wetting layer, and the supply of the wetting layer carriers. The fitted lifetimes decrease with the increase of the injection currents under gain unsaturation, slightly decrease with the decrease of inhomogeneous broadening of QDs, and increase with the increase of detuning wavelength between continuous signal and pulse signal and the increase of the pulse energy.

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions. Based on photoluminescence in an antibunching experiment, we analyzed the emission lifetime of QDs by using stretched exponentials. The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission. An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution. The power law exponent under high excitation power was correlated with a higher Auger ionization rate. Using the parameters obtained from stretched exponential function and power law, the antibunching phenomena at different time and under different excitation intensity were analyzed.

Quantum efficiency of GaAs/AlGaAs thin films with two-dimensional photonic crystals

The optical properties of GaAs/AlGaAs thin films with photonic crystals were investigated by measuring their photoluminescence spectra. The spectral intensities, lifetimes, and quantum efficiencies decreased greatly compared with those in blank material without photonic crystals. The quantum efficiencies in the material were also calculated from spectral intensities and lifetimes and the quantum efficiencies calculated from those two methods agreed with each other to some extent.

Carrier spin relaxation in (Ga, Mn) As at room temperature

In this paper, the excitation energy density dependence of carrier spin relaxation is studied at room temperature for the as-grown and annealed (Ga, Mn) As samples using femtosecond time-resolved pump-probe Kerr spectroscopy. It is found that spin relaxation lifetime of electrons lengthens with increasing excitation energy density for both samples, and the annealed ( Ga, Mn) As has shorter carrier recombination and electron spin relaxation lifetimes as well as larger Kerr rotation angle than the as-grown ( Ga. Mn) As under the same excitation condition. which shows that DP mechanism is dominant in the spin relaxation process for ( Ga, Mn)As at room temperature. The enhanced ultrafast Kerr effect in the annealed (Ga,Mn)As shows the potential application of the annealed ( Ga, Mn) As in ultrafast all-optical spin switches, and also provides a further evidence for the p-d exchange mechanism of the ferromagnetic origin of (Ga, Mn) As.

Surface recombination in GaAs thin films with two-dimensional photonic crystals

The dynamics of spontaneous emission from GaAs slabs with photonic crystals etched into them are investigated both theoretically and experimentally. It is found that the intensity of spontaneous emission decreases significantly and that photonic crystals significantly shorten the lifetime of emission. The mechanics of enhancement and the reduction of emission from photonic crystals are analyzed by considering the surface recombination of GaAs. The measured and calculated lifetimes agree at a surface recombination velocity of 1.88x10(5) cm/s.

Photostability of single-photon emission from a single quantum dot in the 650-nm wavelength band at room temperature

The photoluminescence correlation from a single CdSe nanocrystal under pulsed excitation is studied, and a single photon is realized at wavelength 655 nm at room temperature. The single colloidal CdSe quantum dot is prepared on a SiO2/silicon surface by a drop-and-drag technique. The long-term stability of the single-photon source is investigated; it is found that the antibunching effect weakens with excitation time, and the reason for the weakening is attributed to photobleaching. The lifetimes of photoluminescence from a single quantum dot are analyzed at different excitation times. By analyzing the probability distribution of on and off times of photoluminescence, the Auger assisted tunneling and Auger assisted photobleaching models are applied to explain the antibunching phenomenon.

Full-color emission from In2S3 and ln(2)S(3): Eu3+ nanoparticles

New observations on the luminescence Of In2S3 and europium-doped In2S3 nanoparticles show a green (5 10 nm) emission from In2S3 and In1.8Eu0.2S3 nanoparticles while a blue (425 nm) emission is observed from ln(1.6)Eu(0.4)S(3) nanoparticles. Both the blue and green emissions have large Stokes shifts of 62 and 110 nm, respectively. Excitation with longer-wavelength photons causes the blue emission to shift to a longer wavelength while the green emission wavelength remains unchanged. The lifetimes of both the green and blue emissions are similar to reported values for excitonic recombination. When doped with Eu3+, in addition to the broad blue and green emissions, a red emission near 615 nm attributed to Eu3+ is observed. Temperature dependences on nanoparticle thin films indicate that with increasing temperature, the green emission wavelength remains constant, however, the blue emission shifts toward longer wavelengths. Based on these observations, the blue emission is attributed to exciton recombination and the green emission to Indium interstitial defects. These nanoparticles show full-color emission with high efficiency, fast lifetime decays, and good stability; they are also relatively simple to prepare, thus making them a new type of phosphor with potential applications in lighting, flat-panel displays, and communications.

Luminescence temperature and pressure studies of Zn2SiO4 phosphors doped with Mn2+ and Eu3+ ions

Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+ Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be -25.3 +/- 0.5 and -28.5 +/- 0.9 meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+ Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. (c) 2005 Elsevier B.V. All rights reserved.

Recombination kinetics of Te isoelectronic centers in ZnSTe

The recombination kinetics of Te isoelectronic centers in ZnS1-xTex (0.0065 less than or equal to x less than or equal to 0.85) alloys is studied by time-resolved photoluminescence (TRPL) at low temperature. The measured radiative recombination lifetimes of different Te bound exciton states are quite different, varying from a few nanoseconds to tens of nanosecond. As the bound exciton state evolves from a single Te impurity (Te-1) to larger Te clusters (Te-n, n=2,3,4), the recombination lifetime increases. It reaches maximum (similar to40 ns) for the Te-4 bound states at x=0.155. The increase of the exciton lifetime is attributed to the increasing exciton localization effect caused by larger localization potential. In the large Te composition range (x > 0.155), the exciton recombination lifetime decreases monotonically with Te composition. It is mainly due to the hybridization between the Te localized states and the host valence band states. The composition dependences of the exciton binding energy and the photoluminescence (PL) line width show the similar tendency that further support the localization picture obtained from the TRPL measurement. (C) 2005 American Institute of Physics.

Stability of GaAs photocathodes under different intensities of illumination

The photocurrent curves of reflection-mode GaAs photocathodes as a function of time, when were illuminated by white light with an intensity of 0, 33 and 100 Ix, respectively, were measured using a multi-information measurement system. The calculated lifetimes of cathodes are 320, 160 and 75 min, respectively, showing that the stability of cathodes degraded with the increase of light intensity. The lifetime of cathode, illuminated by white light with an intensity of 100 Ix, while no photocurrent was being drawn during the illumination, was 100 min. Through comparison, we found that the influence of illumination on cathodes stability is greater than that of photocurrent. The quantum-yield curves of cathodes as a functions of time, when illuminated by white light with an intensity of 33 Ix, were measured also. The measured results show that the shape of the yield curves changes with increasing illumination time due to the faster quantum-yield degradation rate of low energy photons. Based on the revised quantum-efficiency equations for the reflection-mode cathodes, the variation of yield curves are analyzed to be due to the intervalley diffusion of photoelectrons and the evolution of the surface potential barrier profile of the photocathodes during degradation process.

Spin relaxation dynamics in InAs monolayer and submonolayer

By using time-resolved photoluminescence and time-resolved Kerr rotation, we have studied the unique electron spin dynamics in InAs monolayer (ML) and submonolayer (SML), which were sandwiched in GaAs matrix. Under non-resonant excitation, the spin relaxation lifetimes of 3.4 ns and 0.48 ns were observed for 1/3 ML and I ML InAs samples, respectively. More interestingly, the spin lifetime of the 1/3 ML InAs decreased dramatically under resonant excitation, down to 70 ps, while the spin lifetime of the 1 ML sample did not vary much, changing only from 400 to 340 ps. These interesting results come from the different electron-hole interactions caused by different spatial electron-hole correlation, and they provide a direct evidence of the dominant spin relaxation process, i.e. the BAP mechanism. Furthermore, these new results may provide a valuable enlightenment in controlling the spin relaxation and in seeking new material systems for spintronics application.

Lifetime study of N impurity states in GaAs1-xNx (x=0.1%) under hydrostatic pressure

The lifetimes of a series of N-related photoluminescence lines (A(2)-A(6)) in GaAs1-xNx (x=0.1%) were studied under hydrostatic pressures at similar to 30 K. The lifetimes of A(5) and A(6) were found to increase rapidly with increasing pressure: from 2.1 ns at 0 GPa to more than 20 ns at 0.92 GPa for A(5) and from 3.2 ns at 0.63 GPa to 10.8 ns at 0.92 GPa for A(6). The lifetime is found to be closely correlated with the binding energy of the N impurity states, which is shown either in the pressure dependence for a given emission line or in the lifetime variation from A(2) to A(6). (c) 2006 American Institute of Physics.