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The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods. [ABSTRACT FROM AUTHOR]

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (VGa). Different correlations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of VGa was significantly influenced by the type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. VGa formation was suppressed with increasing temperature for growth from TEGa. On the contrary, enhancement of VGa concentration was observed for growth from TMGa, with cluster formation for the highest temperature of 1100 °C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS, it can be concluded that yellow band luminescence in GaN is likely not connected with VGa; additionally, increased VGa concentration enhances excitonic luminescence. The probable explanation is that VGa prevent the formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested. [ABSTRACT FROM AUTHOR]

The glass‐ceramics (GC) of gadolinium aluminum gallium garnets with the expected composition of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be (GAGG:Ce and GAGG:Ce,Be, respectively) are fabricated by crystallization from the Gd2O3–Al2O3–Ga2O3–CeO2–SiO2–BeO (Gd:Ga:Al ratio is close to 3:2:3) glasses. The influence of Be2+ co‐doping (including doping level) on the luminescent properties of the GAGG is demonstrated. In particular, Be co‐doping results in the suppression of the Ce3+‐related radioluminescence (RL) and as a consequence, the light yield is lowered as well. The conclusion is made that Be2+ creates effective electron or hole trapping centers. [ABSTRACT FROM AUTHOR]

InGaN/GaN multiple quantum well structures are studied as potential candidates for superfast scintillation detectors and show the leading decay time of around 1 ns and intense luminescence. Photoluminescence properties of these structures with quantum well (QW) numbers ranging from 10 to 60 are described and discussed. It is shown that with increased QW number, the luminescence efficiency of the whole structure increases due to the V-pits of a sufficient size suppressing non-radiative recombination. Suppression of the non-radiative recombination near dislocations is demonstrated by the cathodoluminescence measured at different acceleration voltages. The optimal V-pit size is found to be in the range from 200 to 300 nm, which is obtained for structures with 40 QWs. On the other hand, when the V-pit size exceeds the optimal value, the PL intensity decreases by strong V-pit coalescence, which is observed for structures with 60 QWs. For further increasing the active region thickness, which helps to enhance the detection efficiency of high-energy irradiation, it is necessary to find a way to control the V-pit size. Excitation–emission maps are measured to elucidate how efficiently the structures are excited depending on the light wavelength and the QW number. It is shown that the wavelength for most efficient excitations of InGaN/GaN QWs is 362 nm. With increasing number of QWs, their fast excitonic luminescence is considerably enhanced, whereas slow defect band luminescence is suppressed. Time-resolved measurements with soft X-ray excitation also support our conclusions, showing suppressed non-radiative recombination for structures with higher QW numbers. The fastest decay component increases from 0.25 ns for a structure with 10 QWs to 1.1 ns for a structure with 60 QWs. [ABSTRACT FROM AUTHOR]

In this work we compare luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with 10 and 30 QWs. The aim is to increase the intensity of faster blue QW emission and decrease the luminescence of the QW defect band, showing a slower luminescence decay time, which is undesired for fast scintillator applications. We demonstrate that increasing the number of InGaN QWs is an efficient method to reach this goal. The luminescence improvement of the sample with higher number of QWs is explained by the influence of the increased size of V‐pits with increased QW number. Thinner QWs on the side wall of V‐pits serve as barriers which separate carriers from dislocations penetrating through the V‐pit centre, supressing thus the non‐radiative and radiative recombination on defects. Based on cathodoluminescence (CL) results, the scintillator structure design is discussed. Scintillator structures with higher number of QWs can take advantage of both, improved luminescence efficiency and thicker active region. [ABSTRACT FROM AUTHOR]