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ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity. [ABSTRACT FROM AUTHOR]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 °C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 °C. [ABSTRACT FROM AUTHOR]

We report results from theoretical and experimental investigations of GaInNAs/GaAs quantum well structures. Optical transition energies for samples with different In and N concentrations were determined by photoluminescence measurements. The results show that the reduction of the ground-state transition energy by the introduction of N decreases with increasing In concentration. The experimental data are compared with calculations using the effective-mass approximation. Modifications of the band-gap energy due to N incorporation were accounted for using the two-level repulsion model. Proper effective-mass and band offset values, based on recent experimental work, were used. Calculated and measured transition energies show good agreement. The critical thickness, lattice constant, strain, and optical transition energies are discussed for GaInNAs/GaAs quantum well structures tuned for emission at 1.3 and 1.55 μm, in particular. Such a simple model, within the effective-mass approximation, is a very useful guide for device design. [ABSTRACT FROM AUTHOR]

InAs quantum dots (QDs) have been investigated using optical spectroscopy, in order to understand the experimental observation of strong enhancement of their photoluminescence efficiency. When a tunneling barrier is introduced between the InAs layer and the GaAs cap layer, the intensity of the InAs QD emission increases by more than an order of magnitude at the excitation density of 60 W/cm². The enhancement of the optical recombination efficiency is due to the suppression of the nonradiative transitions in the wetting layer. The strong enhancement of the InAs emission can lead to an increase in the optical gain of the InAs laser structure. [ABSTRACT FROM AUTHOR]

ZnO nanotube arrays were synthesized on zinc foil by a simple solvothermal approach. In this approach, zinc foil was used not only as a substrate but also as a zinc-ion source for the direct growth of ZnO nanotube arrays. X-ray diffraction (XRD) analysis and Scanning electron microscope (SEM) images, indicated that the structure of the ZnO nanotube arrays on the zinc foil substrate was single-crystalline with a wurtzite structure. The optical properties of the ZnO nanorod arrays were characterized by photoluminescence spectroscopies and Raman. Photoluminescence exhibited strong UV emission and a broad deep-level (visible) emission emission at with 325 nm excitation. A possible mechanism is also proposed to account for the growth of the ZnO nanotube arrays. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A set of bulk ZnO samples implanted with O and Zn at various densities were investigated by photoluminescence. The implantation concentration of O and Zn is varied between 1×1017/cm3 and 5×1019/cm3. The samples were thermally treated in an oxygen gas environment after the implantation. The results clearly show the influence of O and Zn implantations on the deep-level emission. By comparing the photoluminescence spectra for the samples with different implantations, we can conclude that the VZn is responsible to the observed deep-level emission. In addition, a novel transition at the emission energy of 3.08 eV at 77 K appears in the O-implanted sample with 5×1019/cm3 implantation concentration. The novel emission is tentatively identified as O-antisite OZn. [ABSTRACT FROM AUTHOR]

In rare-earth ion doped chalcogenide glass, the impacts of glass homogenization on optical properties were studied in this work. A series of Ge24Ga10Se65:Er1 glasses were fabricated by melt-quenching method under the same condition with different melting time. The structure of the obtained glasses was characterized, absorption and emission spectra were recorded, and lifetime of the 4I13/2 state of Er3+ ions was measured as well. It is found that the melting time does not have obvious influence on glass structure, absorption and emission properties of erbium ions. A significant improvement on lifetime was noticed with the increase of melting time. [ABSTRACT FROM AUTHOR]

ZnO nanorods arrays are respectively prepared under different vapor pressures with opening (OZN) or sealing (SZN) of the beaker. The results from time-resolved photoluminescence measurements indicate that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 °C post-thermal treatment of OZN samples. The results from X-ray photoelectron spectroscopy measurements reveal that the main reason for this phenomenon is that the surfaces of the SZN samples are attached by groups related to NH3 instead of the main surface recombination centers such as OH and H groups in the OZN samples. The ammonia surface treatment on both OZN and SZN samples further testifies that the absorption of the groups related to NH3 does not contribute to the surface recombination on the ZnO nanorods. Low temperature (1.8 K) decay curves for samples grown in an open beaker (OZN), an open beaker with post-growth annealing at 500 °C in air (OZN-A), and a sealed beaker (SZN) are fitted by two exponential decays according to the equation I(t) = ASe−t/τS + ABe−t/τB. The inset indicates that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 °C post-thermal treatment of OZN samples. [ABSTRACT FROM AUTHOR]