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The femtosecond dynamics of the photochemistry of a simple merocyanine dye trans isomer is examined. The occurrence of deprotonation compared to isomerization is investigated.

Femtosecond pump-probe techniques can be used to investigate the power dependence of the transient absorption spectrum of CdSe nanoparticle colloids with size distribution of 4.0 plus or minus 0.4 nm diameter. It is possible to observe the two main exciton bleaching (negative absorption) bands.

Femtosecond laser spectroscopy is used in studying the formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with 1,4-benzoquinone and 1,2-naphthoquionone as the adsorbed electron acceptors. The growth and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were also examined. Results indicated that the electron transfer from the NPs to the quinone occurs after thermalization of the excited hot electrons based on the ultrashort rise times of the bleach at the band-gap energy. The decay times for the electron acceptor radical anions is similar to the CdSe bleach recovery time of 3 ps.

Transmission electron microscopy and optical absorption spectroscopy were used to investigate the shape of gold nanorods in micellar solution is transformed by exposure to laser pulses of different pulse width and energies at 800 nm. Results showed that the nanorods were fragmented at near-spherical particles of comparable volumes by femtosecond irradiation at moderate and high energies. Moreover, smaller near-spherical particles were formed by nonsecond pulses at moderate energies.

A study was conducted to analyze the time dependence of the spectral diffusion of the optical hole for the CdS quantum dot and the CdS/HgS/CdS quantum dot quantum well nanoparticles. The quantum dot well structure was prepared by forming a CdS core and displacing the surface Cd2+ ions by Hg2+ ions. Experimental results indicated that the HgS shell acted as a barrier for the 1S(sub 1/2) hole rather than a well.

Femtosecond pump–probe absorption spectroscopy is used to investigate the role of Er3+ dopants in the early relaxation pathways of photoexcited Si nanocrystals. The fate of photoexcited electrons in three different Si nanostructures was studied and correlated with the effect of Er-doping and the nature of the dopant architecture. In Si nanocrystals without Er3+ dopant, a trapping component was identified to be a major electron relaxation mechanism. Addition of Er3+ ions into the core or surface shell of the nanocrystals was found to open up additional nonradiative relaxation pathways, which is attributed to Er-induced trap states in the Si host. Analysis of the photodynamics of the Si nanocrystal samples reveals an electron trapping mechanism involving trap-to-trap hopping in the doped nanocrystals, whereby the density of deep traps seem to increase with the presence of erbium. To gain additional insights on the relative depths of the trapping sites on the investigated nanostructures, benzoquinone was used as a surface adsorbed electron acceptor to facilitate photoinduced electron transfer across the nanocrystal surface and subsequently assist in back electron transfer. The established reduction potential (-0.45 V versus SCE) of the electron acceptor helped reveal that the erbium-doped nanocrystal samples have deeper trapping sites than the undoped Si. Furthermore, the measurements indicate that internally Er-doped Si have relatively deeper trapping sites than the erbium surface-enriched nanocrystals. The electron-shuttling experiment also reveals that the back electron transfer seems not to recover completely to the ground state in the doped Si nanocrystals, which is explained by a mechanism whereby the electrons are captured by deep trapping sites induced by erbium addition in the Si lattice. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reply is given to Gopinath's comment on photoelectronic spectroscopic investigation of titania nanoparticles. Burda and Gole feel that they have comprehensively given details of XPS investigation of photoelectronic spectroscopic investigations of nitrogen-doped titania nanoarticles.

Studies electron dynamics in gold nanoparticles by femtosecond transient absorption spectroscopy. Non-Fermi electron distribution; Effects of exciting the interband transitions; Simulations of the optical response arising from thermalized and nonthermalized electron distributions; Differences between the response from the two electron distributions.

Detailed study of the effects of n-butylamine on the CdSe NP near band-edge fluorescence as well as on the picosecond bleach recovery is presented. A comparison of the steady state and dynamic fluorescence of fresh and aged NP samples is described.

Perovskite solar cells have drawn much attention and achieved efficiencies over 22%, but relatively little is known about the long-term stability under photovoltaic operation. So far, stability studies have reported about the importance of degradation of each layer, but little to no consideration has been given to the whole device architecture. We investigated the stability of perovskite solar cells in order to fundamentally understand the mechanism behind efficiency improvement/degradation during device operation. We found that during operation the interfaces of the perovskite and the electron-transport layer (ETL), meso-porous TiO2, further intermix with each other, which leads to improved power conversion efficiency (PCE) during the initial operation of these solar cells. The operation-induced structural changes are examined directly by X-ray photoelectron spectroscopy (XPS) with in situ low-energy Ar+ sputtering and time-of-flight secondary ion mass spectrometry (ToF-SIMS) with C60 sputtering. In addition, this study describes that the primary cause of irreversible degradation during operation is due to the expansion of TiO2 and ion migration throughout the perovskite solar cell. [ABSTRACT FROM AUTHOR]

Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection. [ABSTRACT FROM AUTHOR]