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Quantum dots can be used in white LEDs for lighting applications to fill the spectral gaps in the combined emission spectrum of the blue pumping LED and a broad band phosphor, in order to improve the source color rendering properties. Because quantum dots are low scattering materials, their use can also reduce the amount of backscattered light which can increase the overall efficiency of the white LED. The absorption spectrum and narrow emission spectrum of quantum dots can be easily tuned by altering their synthesis parameters. Due to the re-absorption events between the different luminescent materials and the light interaction with the LED package, determining the optimal quantum dot properties is a highly non-trivial task. In this paper we propose a methodology to select the optimal quantum dot to be combined with a broad band phosphor in order to realize a white LED with optimal luminous efficacy and CRI. The methodology is based on accurate and efficient simulations using the extended adding-doubling approach that take into account all the optical interactions. The method is elaborated for the specific case of a hybrid, remote phosphor white LED with YAG:Ce phosphor in combination with InP/CdxZn1-xSe type quantum dots. The absorption and emission spectrum of the quantum dots are generated in function of three synthesis parameters (core size, shell size and cadmium fraction) by a semi-empirical 'quantum dot model' to include the continuous tunability of these spectra. The sufficiently fast simulations allow to scan the full parameter space consisting of these synthesis parameters and luminescent material concentrations in terms of CRI and efficacy. A conclusive visualization of the final performance allows to make a well-considered trade-off between these performance parameters. For the hybrid white remote phosphor LED with YAG:Ce and InP/CdxZn1-xSe quantum dots a CRI Ra = 90 (with R9>50) and an overall efficacy of 110 lm/W is found.

RESUMEN

Luminescent materials are widely used in white LEDs to convert part of the blue LED light into light with a longer wavelength, resulting in white light when both colors are well mixed. One way to integrate the luminescent material in the LED package is to deposit a thin luminescent layer on a planar carrier or disperse luminescent particles in the carrier material and then position the resulting wavelength conversion plate above one or more LEDs. It is very important that these wavelength conversion plates have the right properties to ensure homogeneous white light with a high efficiency and desired correlated color temperature (CCT). Key properties are the absorption and emission spectrum and the scattering and absorption coefficients. These properties strongly influence the color of the resulting light, but also the efficiency and the angular uniformity. This work describes an extensive study of the effect of the scattering and absorption coefficients in terms of the desired CCT. A computationally efficient extended Adding-Doubling method is used for the simulation of the light distribution and conversion in the planar wavelength conversion element. Ultimately an optimal combination with a high efficiency and low angular color deviation is desired. Different systems are investigated and optimal coefficients are found. With these findings a more targeted approach can be used in the manufacturing of wavelength conversion plates for white LEDs. The addition of scatterers or non-scattering luminescent particles can be used to obtain optimal scattering properties of the wavelength conversion plate.

RESUMEN

To perform adequate simulations of luminescent cascade systems, a hybrid method combining a commercial ray tracer and a programming tool is presented. True Monte Carlo algorithms for luminescent materials, treating each ray individually, are adapted to allow wavelength conversion of ray sets. Two solutions for the wavelength conversion of ray sets are discussed: a random approach, where absorption events are randomly selected to create emission events, and a combined approach, where information from multiple absorption events is combined to create emission events. Both methods are applied to simulate the performance of a virtual remote phosphor light-emitting diode module. When using the combined approach, the required computation time to achieve sufficient accuracy is a factor 2 lower, compared to the time required when applying the random approach.

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Yersinia ruckeri is the etiological agent of enteric redmouth disease, a systemic infection which mainly affects salmonids. Although this important freshwater pathogen was discovered in 1966, little is known about its virulence mechanisms. In the present study, the interactions with rainbow trout head kidney macrophages were investigated. In vitro experiments were performed to measure uptake, intracellular survival, respiratory burst response and macrophage viability after exposure to Y. ruckeri. Additionally, the fate of Y. ruckeri in the head kidney after immersion infection was studied in vivo. Results show that Y. ruckeri induced the production of reactive oxygen species and that this response peaked at around 3 h after exposure. Despite these toxic substances, Y. ruckeri is able to survive in vitro inside trout macrophages for at least 24 h. Transmission electron microscopy demonstrated that Y. ruckeri bacteria are sequestered in autophagocytic compartments without fusion with primary lysosomes. Inside these compartments, bacteria were capable of replicating. Immersion infection of juvenile rainbow trout resulted in steadily increasing numbers of bacteria in the head kidney over time. As the infection progressed, Y. ruckeri shifted from a predominantly extracellular phase during the first week after infection to an intracellular phase inside the host macrophages from day 7 onwards. In conclusion, this study clearly demonstrates the capacity of Y. ruckeri to survive in rainbow trout macrophages in vitro as well as in vivo, confirming its facultative intracellular nature.

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RESUMEN

The significant disadvantages accompanied with the use of antibiotics in aquaculture, emphasize the need for developing alternative disease control strategies, like novel vaccine approaches and immunostimulating measures. Several studies have already pointed out the ability of heat shock proteins (HSPs) to modulate innate and adaptive immune responses, what makes them potent candidates for the development of a new disease prevention method. In this study, the use of self and non-self heat shock proteins as a new prophylactic treatment against bacterial diseases in freshwater aquaculture was investigated. Therefore, an infection model was developed with platyfish as a host for Yersinia ruckeri infections. In this infection model, the effect of different treatments with HSPs on the survival of the fish after bacterial infection was tested: non-lethal heat shock, intracoelomal injection with two recombinant bacterial HSPs, GroEL and DnaK, and a combination of a non-lethal heat shock and an injection with bacterial HSPs. The results show that a non-lethal heat shock could not protect fish against a subsequent infection with Y. ruckeri. However, when the fish received an injection with bacterial HSPs, Y. ruckeri induced mortality was reduced. This effect became significant when the administration of bacterial HSPs was combined with a non-lethal heat shock. These data suggest a possible role for heat shock proteins as an immunostimulating treatment in fish against bacterial infections.

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