Browsing by Subject "Donor concentrations"

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Open Access
Excitonic improvement of colloidal nanocrystals in salt powder matrix for quality lighting and color enrichment
(OSA - The Optical Society, 2016) Erdem, T.; Soran-Erdem, Z.; Kelestemur, Y.; Gaponik, N.; Demir, Hilmi Volkan
Here we report excitonic improvement in color-converting colloidal nanocrystal powders enabled by co-integrating nonpolar greenand red-emitting nanocrystal energy transfer pairs into a single LiCl salt matrix. This leads to nonradiative energy transfer (NRET) between the cointegrated nanocrystals in the host matrix. Here we systematically studied the resulting NRET process by varying donor and acceptor concentrations in the powders. We observed that NRET is a strong function of both of the nanocrystal concentrations and that NRET efficiency increases with increasing acceptor concentration. Nevertheless, with increasing donor concentration in the powders, NRET efficiency was found to first increase (up to a maximum level of 53.9%) but then to decrease. As a device demonstrator, we employed these NRET-improved nanocrystal powders as color-converters on blue light-emitting diodes (LEDs), with the resulting hybrid LED exhibiting a luminous efficiency >70 lm/Welect . The proposed excitonic nanocrystal powders potentially hold great promise for quality lighting and color enrichment applications.
Open Access
The substrate temperature dependent electrical properties of titanium dioxide thin films
(2010) Yildiz, A.; Lisesivdin, S.B.; Kasap, M.; Mardare, D.
Titanium dioxide thin films were obtained by a dc sputtering technique onto heated glass substrates. The relationship between the substrate temperature and the electrical properties of the films was investigated. Electrical resistivity measurements showed that three types of conduction channels contribute to conduction mechanism in the temperature range of 13-320 K. The temperature dependence of electrical resistivity between 150 and 320 K indicated that electrical conductioninthe films was controlled by potential barriers caused by depletion of carriers at grain boundaries. The conduction mechanism of the films was shifted from grain boundary scattering dominated band conduction to the nearest neighbor hopping conduction at temperatures between 55 and 150 K. Below 55 K, the temperature dependence of electrical resistivity shows variable range hopping conduction. The correlation between the substrate temperature and resistivity behaviorisdiscussed by analyzing the physical plausibility of the hopping parameters and material properties derived by applying different conduction models. With these analyses, various electrical parameters of the present samples such as barrier height, donor concentration, density of states at the Fermi level, acceptor concentration and compensation ratio were determined. Their values as a function of substrate temperature were compared. © Springer Science+Business Media, LLC 2009.