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The present study focuses on the photoluminescence (PL) properties of ZnO films prepared by the reaction of water and zinc. Temperature-dependent PL characteristics of the ZnO films have been investigated in the range from 15 to 260 K. The PL spectrum at 15 K is dominated by neutral donor-bound exciton (D0X) emissions. The emission line at about 3.304 eV can be due to the transition of free electrons to neutral acceptor states (eA0). It is suggested that the ultraviolet emission at room temperature can be attributed to the incorporation of eA0 and free exciton (FX) transitions, rather than sole FX. According to the temperature behavior of green band, it is further confirmed that the green emission is mainly related to the singly ionized oxygen vacancies. [ABSTRACT FROM AUTHOR]

The present work reports on the tunable optical emission from oxygen vacancies in ZnO nanorods. The common green luminescence at room temperature originated from oxygen vacancy defects can be mediated by simply controlling pH values of alkaline solutions without the introduction of any intentional dopants. The peak energies of the green band are found to be monotonously tuned in the range from 2.17 to 2.47 eV, which could promote the applications of tunable wavelength ZnO optoelectronic devices. The temperature dependent behavior of exciton transitions and oxygen vacancy recombinations in ZnO nanorods is investigated in detail. It is suggested that the localized bound exciton (LBX) attached near the lateral facets of ZnO nanorods could survive up to nearly room temperature due to the large binding energy. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrated the enhancement of electron transfer from CdSe/ZnS core/shell quantum dots (QDs) to TiO2 films via thermal annealing by means of steady-state and time-resolved photoluminescence (PL) spectroscopy. The significant decrease in PL intensities and lifetimes of the QDs on TiO2 films was clearly observed after thermal annealing at temperature ranging from 100°C to 300°C. The obtained rates of electron transfer from CdSe core/shell QDs with red, yellow, and green emissions to TiO2 films were significantly enhanced from several times to an order of magnitude (from ∼107 s−1 to ∼108 s−1). The improvement in efficiencies of electron transfer in the TiO2/CdSe QD systems was also confirmed. The enhancement could be considered to result from the thermal annealing reduced distance between CdSe QDs and TiO2 films. The experimental results revealed that thermal annealing would play an important role on improving performances of QD based optoelectronic devices. [Copyright &y& Elsevier]

Abstract: Optical properties of Mn-doped Zn x Cd1− x S nanocrystals were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy. The doped nanocrystals with PL quantum yield up to 29% were synthesized by growing a thin ZnS layer on the MnS core and then growing a CdS layer with different thicknesses using nucleation-doping strategy. The absorption band edge of Zn x Cd1− x S nanocrystals was tuned from 425 to 475nm by growing the CdS layer with various thicknesses under different Zn/Cd molar ratios to vary the composition. The PL band of Mn-doped nanocrystals was found to originate from emissions of Mn2+ ions and defect states. [Copyright &y& Elsevier]

Abstract: ZnO films with strong c-axis-preferred orientation have been prepared by a single source chemical vapor deposition technique using zinc acetate as source material at the growth temperature of 230°C. The strong UV and blue emissions were observed in the photoluminescence spectra of as-grown films. A small quantity of residual zinc acetate was reserved on the surface of as-grown ZnO films and the emission mechanism of blue luminescence was nearly related to the CH3COO– of unidentate type. The blue emission disappeared and the green emission appeared after annealing treatment. The green emission is related to the singly ionized oxygen vacancies. [Copyright &y& Elsevier]

Herein, a novel molecular SO2‐Bri‐DSB based on the sulfone‐bridged distyrylbenzene derivative is synthesized, and its organic crystal is fabricated. It has a very high photoluminescence (PL) quantum efficiency in the solution and crystalline state, i.e., dual‐state emission (DSE), and the corresponding PL mechanism is clarified in detail using the transient absorption and transient PL test. The PL behaviors in the monomolecular state and organic crystal are compared. In addition, the optical anisotropy of the SO2‐Bri‐DSB crystal is thoroughly investigated using various polarization‐dependent spectroscopy techniques. The time evolution of anisotropy is composed of a step behavior caused by the anisotropy of the electronic transition and a slow enhancing process with a lifetime of 4.86 ns, which is governed by the change in emission lifetime due to the anisotropy. The space‐resolved evolution of the optical anisotropy is investigated using the polarization‐dependent light wave‐guiding test and exhibits that the emission anisotropy gradually decreases with length, and it has a longer effective propagation length than the polarization emission signal. The findings provide insight into the intrinsic optical anisotropy of single‐molecular crystals and indicate that these materials have enormous potential in the domains of polarization lighting and display. [ABSTRACT FROM AUTHOR]

Abstract: Temperature-dependent photoluminescence (PL) spectroscopy of CuInS2 core and CuInS2/ZnS core–shell quantum dots (QDs) was studied for understanding the influence of a ZnS shell on the PL mechanism. The PL quantum yield and lifetime of CuInS2 core QDs were significantly enhanced after the QD surface was coated with the ZnS shell. The temperature dependences of the PL energy, linewidth, and intensity for the core and core–shell QDs were studied in the temperature range from 92 to 287K. The temperature-dependent shifts of 98meV and 35meV for the PL energies of the QDs were much larger than those of the excitons in their bulk semiconductors. It was surprisingly found that the core and core–shell QDs exhibited a similar temperature dependence of the PL intensity. The PL in the CuInS2/ZnS core–shell QDs was suggested to originate from recombination of many kinds of defect-related emission centers in the interior of the cores. [Copyright &y& Elsevier]

Both normal and ripple-like CdS microbelts (MBs) were prepared and their optical properties were investigated by photoluminescent and Raman measurements. One emission at ~510 nm for normal CdS MBs and two emissions around 513 and 725 nm for ripple-like one were observed. The longitudinal optical phonon mode (1LO) at ~304 cm-1 and its overtone mode (2LO) at ~605 cm-1, multiphonon processes and surface phonon peaked at 281 cm-1 were observed, the larger integrated intensities ratio of 2LO to 1LO indicates a strong exciton-phonon coupling interaction. Furthermore, more than 4 times larger enhanced Raman scattering for the ripple-like MBs than the normal one were observed, and the enhanced Raman scattering is mainly associated with the surface defects, which lead to a strong Fröhlich interaction through the charge transfer, not by the deformation potential through surface plasmon enhancement. [ABSTRACT FROM AUTHOR]