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Parameters characterizing the charge state of dielectrics

Abstract

This paper presents three physical sources of the electric field in dielectrics: excess free volume charges with the distribution qv(x,y,z), free surface charges with the distribution qs(x,y,z) and frozen polarization state in the dielectric. They have a deciding influence on the parameters of the electret, in particular they determine the total lifetime of the electret and technical components made of it. The indeterminacy related to the mutual proportions of the spatial and surface charges was discussed: one can find an infinite number of distributions of surface qse(x,y,z) and spatial qve(x,y,z) charges leading to the same distribution of the electric field E(x,y,z). A general case of electret was considered, where a coexistence of relaxation decay of frozen polarization and Maxwellian relaxation dependent on volume conductivity of the dielectric is assumed. An attempt to interpret the charge lifetime in real electrets was made.

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SiN/SiO2 passivation stack of n-type silicon surface

Abstract

The SiN/SiO2 stack is widely used to passivate the surface of n-type monocrystalline silicon solar cells. In this work, we have undertaken a study to compare the stack layer obtained with SiO2 grown by both rapid thermal and chemical ways to passivate n-type monocrystalline silicon surface. By varying the plateau time and the plateau temperature of the rapid thermal oxidation, we determined the parameters to grow 10 nm thick oxide. Two-step nitric acid oxidation was used to grow 2 nm thick silicon oxide. Silicon nitride films with three refractive indices were used to produce the SiN/SiO2 stack. Regarding this parameter, the minority carrier lifetime measured by means of QSSPC revealed that the refractive index of 1.9 ensured the best passivation quality of silicon wafer surface. We also found that stacks with nitric acid oxidation showed definitely the best passivation quality. In addition to produce the most efficient passivation, this technique has the lowest thermal budget.

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UV-induced photodecomposition of 2, 2′, 4, 4′, 6, 6′-hexanitrostillbene (HNS)

Abstract

HNS (2, 2′, 4, 4′, 6, 6′-hexanitrostillbene) is a heat-resistant photosensitive explosive widely used in the booster charge. Investigation of the photodecomposition mechanism may provide important information for controlling and enhancing the detonation performance, also for the lifetime prediction. The UV-induced photodecomposition of HNS has been subjected to experimental studies. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) demonstrate the formation of NO2 free radicals and nitroso derivatives of HNS upon UV irradiation, which proves well known facts that C-NO2 breaking and removal of oxygen from the nitro group take part in the photodecomposition of HNS.

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Improving color uniformity and color rending index of remote-phosphor packaging white LEDs by co-doping SiO2 and Sr2Si5N8:Eu2+ particles

Abstract

Based on some advantageous properties, such as fast response time, environment friendliness, small size, long lifetime, and high efficiency, white LEDs are increasingly used in common illumination applications. In this research, by co-doping of redemitting Sr2Si5N8:Eu2+ phosphor and adding SiO2 particles to yellow-emitting YAG:Ce phosphor compounds, a new approach for improving color uniformity and color rending index of remote-phosphor structure white LEDs is proposed and demonstrated. The obtained results clearly indicate that the color rendering index (CRI) and color uniformity (ΔCCT) significantly depend on Sr2Si5N8:Eu2+ concentration. The results provide a potential practical solution for manufacturing remote-phosphor white LEDs (RP-WLEDs) in the near future.

Open access
Synthesis and Luminescence Properties of ZrO2:Gd3+, RE3+(RE = Sm3+ ,Er3+) Phosphors

Abstract

In the present study, ZrO2co-doped with Gd3+/Sm3+and Gd3+/Er3+ions have been synthesized using Pechini method. Phase composition, morphology and photoluminescence properties of the synthesized phosphors were investigated by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). After heating at 1200 °C, XRD revealed that the phosphors were crystallized as monoclinic and tetragonal multiphases. SEM images indicated that the phosphors consist of fine and spherical grains with a size around 200 nm to 250 nm. Luminescence studies of these phosphors have been carried out on the emission and excitation, along with lifetime measurements

Open access
Photoluminescence properties of ZrO2:Gd3 +, ZrO2:Gd3 + – Dy3+ and ZrO2:Gd3 + – Yb3+ phosphors by Pechini method

Abstract

Zr0.99Gd0.01O2, Zr0.98Gd0.01Dy0.01O2 and Zr0.98Gd0.01Yb0.1O2 phosphors were synthesized by Pechini method at 1200 °C for 12 h in air. The phosphors were characterized by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). X-ray powder diffraction studies showed that the phosphors were crystallized as monoclinic and tetragonal multiphases. The particle size of the phosphors after heat treatment at 1200 °C was found to be of 200 nm to 250 nm. Luminescence studies on these phosphors have been carried out on the emission and excitation, along with lifetime measurements. The results of emission analysis indicate that the phosphors are expected to find potential applications as new optical materials.

Open access
Investigation on photoluminescence quenching of CdSe/ZnS quantum dots by organic charge transporting materials

Abstract

The effect of different organic charge transporting materials on the photoluminescence of CdSe/ZnS core/shell quantum dots has been studied by means of steady-state and time-resolved photoluminescence spectroscopy. With an increase in concentration of the organic charge transporting material in the quantum dots solutions, the photoluminescence intensity of CdSe/ZnS quantum dots was quenched greatly and the fluorescence lifetime was shortened gradually. The quenching efficiency of CdSe/ZnS core/shell quantum dots decreased with increasing the oxidation potential of organic charge transporting materials. Based on the analysis, two pathways in the photoluminescence quenching process have been defined: static quenching and dynamic quenching. The dynamic quenching is correlated with hole transporting from quantum dots to the charge transporting materials.

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Scanning capacitance microscopy characterization of AIIIBV epitaxial layers

lifetime. The conclusions of the tests were as follows: the largest lifetime had the tip with the conductive diamond coating (DDESP-FM/NANOSensors) but, due to relatively large radius of the tip, the images resolution and contrast were poor. The best images quality was obtained using Cr/Pt (MULTI75E-G/BudgetSensors) and Pt/Ir (SCM-PIT/NANOSensors) coated tips but the second one guaranteed better stability and longer usage. The gold covered AFM tip (PPP-NCSTAu/NANOSensors) had a very short lifetime due to very low hardness of this metal, while the images obtained using Co

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Titanium nitride coatings synthesized by IPD method with eliminated current oscillations

comparison to uncoated tools, 4 fold increase of lifetime; by comparison to TiN coated tool synthesized in standard, current oscillating conditions, 3-fold increase of lifetime. Acknowledgements This work was supported by the National Science Centre within the Project No. 2013/09/B/ST8/02418. References [1] Sokolowski M., J. Cryst. Growth , 54 (1981), 519. 10.1016/0022-0248(81)90507-8 Sokolowski M J. Cryst. Growth 54 1981 519 [2] Sokolowski M., Sokolowska S., J. Cryst. Growth , 57 (1982), 185. 10.1016/0022-0248(82)90265-2 Sokolowski M Sokolowska S

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Carrier recombination in sonochemically synthesized ZnO powders

as (i) lifetime of photogenerated charges with respect to their recombination pathways which, in turn, determines the PL intensity, (ii) concentration of surface defects, (iii) efficiency of the inter-particle charge transfer. It seems to be very likely that the data shown in Fig. 3 indicate that the free carries trapping dynamics is mainly determined by decreasing of the surface defect concentration, provided that the distribution of the grain sizes shifts to smaller values in the sequence of SC1, SC2 and SC3 samples, respectively. This conclusion is supported

Open access