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The test structures for photovoltaic (PV) applications based on zinc oxide nanorods (NRs) that were grown using a low-temperature hydrothermal method on p-type silicon substrates (100) covered with Ag nanoparticles (NPs) were studied. The NPs of three different diameters, i.e., 5-10 nm, 20-30 nm, and 50-60 nm, were deposited using a sputtering method. The morphology and crystallinity of the structures were confirmed by scanning electron microscopy and Raman spectroscopy. It was found that the nanorods have a hexagonal wurtzite structure. An analysis of the Raman and photoluminescence spectra permitted the identification of the surface modes at 476 cm-1 and 561 cm-1. The presence of these modes is evidence of nanorods oriented along the wurtzite c-axis. The NRs with Ag NPs were covered with a ZnO:Al (AZO) layer that was grown using the low-temperature atomic layer deposition technique. The AZO layer served as a transparent ohmic contact to the ZnO nanorods. The applicability of the AZO layer for this purpose and the influence of the Ag nanoparticles on the effectiveness of light acquisition by such prepared PV cells were checked by reflectance and transmittance measurements of the AZO/glass and AZO/NPs/glass reference structures. Based on these studies, the high-energy transmittance edge was assigned to the ZnO energy gap, although it is blueshifted with respect to the bulk ZnO energy gap because of Al doping. It was also shown that the most optimal PV performance is obtained from a structure containing Ag nanoparticles with a diameter of 20-30nm. This result is confirmed by the current-voltage measurements performed with 1-sun illumination. The structures show a plasmonic effect within the short wavelength range: the PV response for the structure with Ag nanoparticles is twice that of the structure without the nanoparticles. However, the influence of the Ag nanoparticle diameters on the plasmonic effect is ambiguous. [ABSTRACT FROM AUTHOR]

We report on zinc oxide thin films grown by atomic layer deposition at a low temperature, which is compatible with a low thermal budget required for some novel electronic devices. By selecting appropriate precursors and process parameters, we were able to obtain films with controllable electrical parameters, from heavily n-type to the resistive ones. Optimization of the growth process together with the low temperature deposition led to ZnO thin films, in which no defect-related photoluminescence bands are observed. Such films show anticorrelation between mobility and free-electron concentration, which indicates that low n electron concentration is a result of lower number of defects rather than the self-compensation effect. [ABSTRACT FROM AUTHOR]

Presents a study which examined the electron spin resonance of the temperature dependence of the ZnS visible photoluminescence. Experimental details; Discussion; Conclusion.

In the current research, europium doped ZnO nanopowders prepared by a microwave hydrothermal method are investigated. The effects of synthesis pressure on the morphologies, crystal structures, and optical properties of Eu-doped ZnO were analyzed by scanning electron microscopy, X-ray diffraction, cathodo- and photoluminescence. From our investigations it can be concluded that the synthesis pressure strongly influences the surface morphology. With the increase of the synthesis pressure from 2 MPa to 10 MPa significant changes can be observed. An increase of the mean crystallites sizes and change of the intensity ratio between the near band edge and defect related deep level emission band of ZnO were observed. [ABSTRACT FROM AUTHOR]

Results of Cd0:7Mn0:3Te magneto-photoluminescence investigations are analyzed. Photoluminescence was measured in a Voigt geometry at the temperature of 1.6 K. Two models describing radiative transition energy are compared with the experimental results of Cd0:7Mn0:3Te luminescence. The energy of recombination transition, employing the complete form of band states splitting description (term due to the Landau splitting included), shows deviation from experiment at B > 2 T. Two possible reasons of discrepancies from the experiment - exchange interaction constants dependence on magnetic field or band edge energies pinning in magnetic field - are discussed. Band edge energies pinning in magnetic field is related to the hybridization of Mn 3d5 levels with the band states of the host. We determine the corrected values of exchange interaction constants (N0α - N0β=3) at magnetic fields B < 5 T. [ABSTRACT FROM AUTHOR]

Abstract: Optical and magneto-optical properties of ZnMnO films grown at low temperature by atomic layer deposition are discussed. A strong polarization of excitonic photoluminescence is reported, surprisingly observed without splitting or spectral shift of excitonic transitions. Present results suggest possibility of Mn recharging in ZnO lattice. Strong absorption, with onset at about 2.1eV, is related to Mn 2+ to 3+ photo-ionization. We propose that the observed strong circular polarization of excitonic emission is of a similar character as the one observed by us for ZnSe:Cr. [Copyright &y& Elsevier]

The results of photoluminescence investigations of zinc oxide nanorods are reported. These nanorods grown on undoped silicon substrates were obtained by low temperature and ultra-fast version of a microwave-assisted hydrothermal method. The photoluminescence investigations show very high quality of the obtained material. From photoluminescence studies we conclude the lack of carrier localization effects. The photoluminescence is dominated by band gap edge emission of bound excitonic (donor bound excitons) origin. Thus, the photoluminescence quenching observed at increased temperatures is associated with thermal ionization of shallow donors. From photoluminescence analysis (changes of photoluminescence line width) a strength of exciton-acoustic phonon coupling is evaluated. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of photoluminescence changes observed at Mn2+ magnetic resonance is presented. CdMnTe samples of a different dimensionality are investigated. We discuss conditions of a strong magnetization quenching at the magnetic resonance and the role of Mn-free carriers spin interactions in spin relaxation processes. Concept of time-resolved experiment is introduced to determine times of spin relaxation. [Copyright &y& Elsevier]

Intra-shell transitions of transition metal and rare earth ions are parity forbidden processes. For Mn2+ ions this is also a spin forbidden process, i.e., light emission should be inefficient. Surprisingly, it has been reported that in nanostructures of ZnMnS the 4T1 to 6A1 intra-shell transition of Mn2+ results in a bright photoluminescence characterized by a short PL decay time. The model of a quantum confined atom was introduced to explain the observed experimental results. It was later claimed that this model is incorrect. Based on the results of our photoluminescence, photoluminescence kinetics, time-resolved photoluminescence, electron spin resonance, and optically detected magnetic resonance investigations, we confirm photoluminescence enhancement and decrease of photoluminescence lifetime and relate these effects to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. This mechanism is active in both bulk and in low-dimensional structures, but is significantly enhanced in nanostructure samples. [ABSTRACT FROM AUTHOR]

Based on the results of optically detected magnetic resonance (ODMR) and time-resolved investigations we relate the observed lifetime shortening of intra-shell Mn2+ emission to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. We show that this mechanism is active both in bulk and in low dimensional structures, such as quantum wells (QWs), quantum dots (QDs) and nanostructures. [Copyright &y& Elsevier]

Origin of a fast component of the photoluminescence (PL) decay of Mn2+ intra-shell 4T1 → 6A1 transition in bulk and quantum dot structures is discussed based on the results of PL, PL kinetics and optically detected magnetic resonance experiments. It is demonstrated that a fast component of the PL decay, reported previously for quantum dot structure and related to quantum confinement effects, is also observed in bulk samples and is very much enhanced upon generation of free carriers. The appearance of this fast component of the PL decay is related to a very efficient spin cross-relaxation between localized spins of Mn ions and spins of free carriers. [Copyright &y& Elsevier]

Two series of ZnO nanopowders obtained by a microwave hydrothermal method are examined. We used two different zinc precursors (zinc chloride (ZnCl2) and zinc nitrate hexahydrate (N2O6Zn·6H2O)). Both types of nanopowders show a bright emission in a visible light, including the band edge emission, which indicates their good crystallographic quality. Results of scanning electron microscopy, photo- and cathodoluminescence investigations are presented. [ABSTRACT FROM AUTHOR]

ZnCoO is one of the most studied and promising semiconductor materials for spintronics applications. In this work we discuss optical and electrical properties of ZnCoO films and nanoparticles grown at low temperature by either atomic layer deposition or by a microwave driven hydrothermal method. We report that doping with cobalt quenches a visible photoluminescence of ZnO. We could observe a visible photoluminescence of ZnO only for samples with very low Co fractions (up to 1%). Mechanisms of photoluminescence quenching in ZnCoO are discussed. We also found that ZnO films remained n-type conductive after doping with Co, indicating that a high electron concentration and cobalt 2+ charge state can coexist. [ABSTRACT FROM AUTHOR]

Abstract: Defects responsible for noise in 4H–SiC p–n junctions are identified using electrical methods. We relate high frequency noise in 4H–SiC p–n junctions to defects active in optical transitions. Results of photoluminescence and optically detected magnetic resonance investigations are presented. [Copyright &y& Elsevier]

Energy up-conversion in chromium doped ZnSe was related to two complementary 2+ → 1+ → 2+ ionization transitions of the chromium ion. Blue emission is observed with relatively high external quantum efficiency of energy up-conversion process (2×10-3 upon the green color optical pumping and at low temperatures). For Cr doped solid alloys of ZnSSe the energy of the pumping light can be tuned and the up-conversion process is still active, as we conclude from photoluminescence (PL) and photo-electron spin resonance (ESR) study. [Copyright &y& Elsevier]

Mechanisms of optical detection of magnetic resonance in wide band gap II-Mn-VI diluted magnetic semiconductor (DMS) are discussed based on the results of photoluminescence (PL), PL kinetics, electron spin resonance (ESR) and optically detected magnetic resonance (ODMR) and optically detected cyclotron resonance (ODCR) investigations. Spin-dependent interactions between localized spins of Mn2+ ions and spins/magnetic moments of free, localized or bound carriers are responsible for the observed ODMR signals. We conclude that these interactions are responsible for the observed rapid shortening of the PL decay time of 4T1→6A1 intra-shell emission of Mn2+ ions and also for the observed delocalization of excitons in low dimensional structures. [Copyright &y& Elsevier]

Photoluminescence studies of CdTe/CdMnTe heterostructures grown either by the atomic layer epitaxy or by a standard molecular beam epitaxy are presented. Morphology of CdTe/CdMnTe interfaces is compared for heterostructures grown by these two methods. The inter-island exciton migration, reported until recently only for high quality GaAs/A1GaAs structures, is observed in our structures with the quantum well grown by the atomic layer epitaxy. This indicates that relatively large and flat quantum well islands with a width differing by one monolayer exist in these samples. The present study, thus, demonstrates an improved quality of interfaces in structures grown by the atomic layer epitaxy. [ABSTRACT FROM AUTHOR]

Distinctly different exciton properties in pseudomorphic and strain relaxed ZnCdSe/ZnSe structures grown on GaAs are demonstrated. For pseudomorphic or partly strained structures temperature stability of photoluminescence depends on the distance from the ZnCdSe quantum well to GaAs/ZnSe interface and less on confinement energies. Densities of two-dimensional localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. These values are compared with the ones reported for contemporary GaAs/AlGaAs structures. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents results of optically detected cyclotron resonance and photoluminescence (PL) kinetics of CdTe/CdMnTe multi-quantum well structures. Indication of the electron and observed heavy hole CR signals; Contribution of impurities to the low temperature PL emission processes; Dominance of ionized donor impurities in low frequency carrier scattering processes.

Examines microwave-induced impact ionization of excitons and shallow donors in Er- and Yb-doped InP. Efficiency of rare-earth photoluminescence; Use of sample grown by metalorganic chemical vapor deposition; Spectral dependence of the impact ionization spectra.

In this paper we report observation of highly efficient Pr3+ 4f–4f emission in ZrO2 (0.5mol.% Pr3+) fine nanocrystals stabilized by Y2O3 (7mol.%). The nanocrystals were obtained via a hydrothermal microwave-driven process followed by heat treatment at 1200°C. The samples excited by 266 or 297nm light exhibit a remarkable sensitizing of Pr3+ photoluminescence. The chromaticity analysis indicates the usability of the studied material as a red luminescent phosphor. [Copyright &y& Elsevier]

Nanoparticles of ZrO 2 :Pr stabilized with ytterbium in the range 0.5%mol.-20%mol. were synthesized. Crystallite sizes depended on Yb concentration. Red luminescence resulting from 1D 2 →3H 4 transition of Pr3+ is present in all the samples. Additionally in the samples calcined at 1200 °C blue-green luminescence from 3P 0 level of Pr3+ was found. This emission was more intense than red one. Intensity of the 3P 0 →3H 4 luminescence depended on ytterbium content and was found to be the highest at 20% mol. Yb. Luminescence study had shown, that ytterbium introduced additional lattice defects. Some quantity of praseodymium activator ions were found to be present at +4 state and changed its valence to +3 as ytterbium content had risen. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles (NPs) doped with iron were synthesized by the microwave-hydrothermal method using various reagents. The properties of these NPs were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), cathodoluminescence (CL) measurements. In the article, we discuss the surprising results of optical studies of ZnO:Fe NPs. The phenomenon of luminescence quenching by the magnetic ion, characteristic for bulk materials, was not observed. We examined three potential reasons for this observation. • ZnO:Fe nanoparticles were synthesized by microwave hydrothermal method using various reagents. • no quenching of luminescence by iron ions in ZnO was found. • XRD, SEM, EDX, PL, CL, XPS measurements were carried out and Mӧssbauer spectra were recorded. [ABSTRACT FROM AUTHOR]

We report on the ground- and excited-state properties of Fe3+ centers in hydrothermally and chemical-vapor-transport grown single ZnO crystals studied by continuous-wave electron-paramagnetic resonance (EPR) under dark and laser-illuminated conditions, pulsed-EPR and magneto-photoluminescence. By use of EPR experiments, the fine-structure parameters of the Fe3+ spin Hamiltonian are determined. Three types of charge-compensated Fe3+ centers are identified and the charge conversion from Fe2+ to Fe3+ is highlighted. The magneto-optical studies of the Zeeman components of the spin-forbidden electric-dipole transitions from excited 4T1(G) to ground 6A1(6S) states of the Fe3+ center indicate the trigonal symmetry of the fine structure of the lowest G8(4T1) excited state. The energy positions of the Zeeman components are measured in the external magnetic field of 8 T rotated in (1210) and (0001) crystal planes. The angular variation of the Zeeman lines exhibits two magnetically nonequivalent Fe3+ centers. These features result from the contribution of high-rank Zeeman terms of dimension BJ³ in the spin Hamiltonian. For the electron spin S = 5/2 system of the trigonal Fe3+ ion, we further demonstrate the tuning of one-photon Rabi oscillations by means of electron spin-echo measurements. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we report on the monocrystalline growth of (00.1) ZnO films on GaN template by the Atomic Layer Deposition technique. The ZnO films were obtained at temperature of 300°C using dietylzinc (DEZn) as a zinc precursor and deionized water as an oxygen precursor. High resolution X-ray diffraction analysis proves that ZnO layers are monocrystalline with rocking curve FWHM of the 00.2 peak equals to 0.07°. Low temperature photoluminescence shows a sharp and bright excitonic line with FWHM of 13meV. [Copyright &y& Elsevier]

Iron doped (in the range from 1 to 10 mol %) ZnO nanoparticles (NPs) were obtained by microwave hydrothermal method. The effects of iron content on morphology, crystal structure, optical and magnetic properties of ZnO nanoparticles were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), cathodoluminescence (CL), photoluminescence (PL) and magnetic measurements. XRD studies revealed presence of ZnFe 2 O 4 foreign phase in NPs for iron doping concentrations above 5% placing the solubility limit of Fe in ZnO NPs near this value. The photoluminescence and cathodoluminescence spectra show an increase of the intensity ratio between near band edge (NBE) and deep level emission band (DLE) of ZnO, which is tentatively related by us with intrinsic cracking of ZnO crystals. The blue-shift of NBE band maxima was observed as a concentration of Fe dopant increases. The results of magnetic measurements indicate superparamagnetic behavior of nanoparticles. • Iron doped ZnO was synthesized using microwave hydrothermal technique. • Concentration of defects in ZnO structure was found to decrease with increasing iron content. • Superparamagnetic behavior was found in synthesized nanoparticles. [ABSTRACT FROM AUTHOR]