Search results for " LED"

Warm white LEDs based on Lumogen® Red and Yellow

2013

One of the most widespread solutions for the production of white LEDs is the frequency downconversion of a part of the light, coming from a blue source, by exciting one or more materials (typically Ce:YAG) that emit at longer wavelength [1]. In this work we report ona simple and less expensive method to fabricate warmwhite-light LEDsusingthe photoluminescence of Lumogen®, a perylene-based polymer dyecommercialized by BASF,that has already beenprovedto be a good substitute for conventi onal inorganic colour conversion [2],[3]. Standard InGaN-based blue LEDs (~ 450 nm) were fabricated on a sapphire substrate by metal organic chemical vapour deposition. Both Lumogen® Yellow, and Red dyes wered…

Warm white LED light by frequency down-conversion of mixed yellow and red Lumogen®

2013

This work reports on the benefits and promising opportunities offered by white LED hybrid technology, based on a mixing perylene-based dyes in order to obtain a warm white light for frequency-down conversion. In a standard Ce:YAG-based white LED, the white light appears cold due to the weakness of red wavelength components in the emission spectrum. In order to obtain a warmer white, one possible solution is to add a red phosphor to the yellow one to move the chromatic coordinates properly, though the luminous efficiency drastically decreases due to the increased light absorption of the coating layer. It is generally believed that the low efficiency of warm white LEDs is the main issue today…

White LED light obtained by frequency down-conversion of perylene-based dyes

2012

Hybrid LEDs pave way to new lighting applications

2013

Many analysts agree that the global lighting market is close to a real revolution: the LED revolution. One of the most widespread solutions for the production of white LEDs is the conversion of a part of the light, coming from a known source, by exciting one or more materials that emit at a longer wavelength. The result is an emission spectrum given by the superposition of the single source and the photoexcited material; the big advantage is that the phenomenon of photoluminescence replaces the further integration of other solid-state devices of different colors. The photoluminescence of a perylene-based polymer dye turned out to be a good substitute for conventional inorganic color convers…

A reaction engineering approach to kinetic analysis of photocatalytic reactions in slurry systems

2016

Abstract The knowledge of the rate equation is fundamental for the assessment of the activity of the photocatalytic material and for the study, design and optimization of photocatalytic reactors. In the case of photocatalytic reactions, the local volumetric rate of photon absorption (LVRPA) affects the reaction rate and its inherently uneven distribution within a “slurry” reactor makes complex a correct kinetic analysis. In the present work it is shown which are the critical aspects of the kinetic analysis in slurry reactors and how to carry out photocatalytic experiments to minimize the misinterpretations of the experimental results. In particular, the influence of the type of illumination…

Tērvetes upes ielejas morfoloģija un veidošanās

2015

Bakalaura darbā apskatīta Tērvetes upes mūsdienu ieleja un procesi, kas to veidojuši laika posmā no Latvijas apledojuma Linkuvas oscilācijas līdz mūsdienām. Teorētiskajā daļā apskatīti galveni noteces ieleju veidotājspēki, kā arī morfoloģiskie procesi, kas veido mūsdienu Latvijas upju ielejām raksturīgos elementus. Sniegts ieskats bakalaura tapšanas gaitā izmantotajās pētniecības metodēs un materiālos. Rezultātu sadaļā analizēti izveidotie ielejas šķērsprofili un garenprofili, kā arī iegūtie Tērvetes un tās ielejas morfoloģiskie rādītāji.

Chemical Bath Deposition as a Simple Way to Grow Isolated and Coalesced ZnO Nanorods for Light-Emitting Diodes Fabrication

2018

A way to grow and characterize isolated and coalesced ZnO nanorods on $p$ -GaN/sapphire structure is presented. Chemical bath deposition can be used to grow ZnO nanorods of device-quality, simply controlling the duration time of the growth process and the concentration of the nutrient solution in the bath. Increasing the duration of the process, as well as the concentration of the solution, leads to compact and sound layers instead of separated nanorods. However, too high concentrations stop the growth process. Light-emitting diodes fabricated on these ZnO-p-GaN heterostructure have a peak of electroluminescence at 400 nm and exhibit interesting electrical and optical properties. Optical po…

Influence of electrodes layout on hydrothermally-grown GaN/ZnO LEDs

2017

Light-emitting diodes (LEDs) based on zinc oxide, with wide direct band gap, have drawn much attention in the last years. ZnO, which is natural n-type, has excellent physical and chemical properties, is inexpensive, abundant and nontoxic. Unfortunately, the preparation of reproducible and high quality p-type ZnO film is comparatively difficult, due to the low solubility of acceptor dopants, self-compensating effects, and acceptor level energy height. Although many groups have reported on ZnO-based homostructure LEDs, the results are controversial as recently reviewed in [1]. Hence, heterojunction LEDs based on ZnO as the nside and GaN as the p-side of the junction have been put forward [2].…

Baltijas ledus ezera krasta līnijas starp Jelgavu un Salaspili

2015

Bakalaura darbā “Baltijas ledus ezera krasta līnijas” tiek īsumā apskatīta Baltijas jūras attīstība, īpašu uzmanību veltot Baltijas ledus ezera attīstībai. Tiek sniegts ieskats arī ģeofizikālajā glacioizostāzijas procesā un tā darbības mehānismā, kā arī apzināti Baltijas ledus ezeram rakstūtīgie akumulācijas un abrāzijas veidojumi. Pētījums tiek veltīts līdz šim šādā ziľā mazizpētītajai teritorijai starp Jelgavu un Salaspili, ar mērķi izpētīt Baltijas ledus ezera krasta veidojumu telpisko un hipsometrisko novietojumu šajā apvidū saistībā ar glacioizostatisko pacelšanos. Pētījuma izstrādē izmantotās metodes ir literatūras studijas, kartogrāfiskās metodes, ģeodēziska zemes virsmas profilēšana…

LiDAR datu izmantošana senā Baltijas ledus ezera krastu identificēšanai

2015

Bakalaura darbā aprakstīta lāzerskenēšanas datu izmantošana un apstrādāšanas metode Baltijas ledus ezera krasta līniju noteikšanai ĢIS vidē, izmantojot 4 datu apstrādes programmas: Bentley Microstation v8i – TerraScan, Surfer 10, Global Mapper 16 un ArcMap 10. Bakalaura darba mērķis ir izmantot LIDAR jēldatus, no kuriem, to apstrādes rezultātā iegūtais reljefa modelis pielietots, lai konstatētu Baltijas ledus ezera krasta līnijas Bgl I, Bgl II un Bgl III stadijas, izdalot Bgl II, Bgl IIIa, Bgl IIIb un Bgl IIIc stadijas. Pētījums ir aktuāls, jo lāzerskenēšanas datu izmantošana mūsdienās ir viena no precīzākajām metodēm reljefa un tā veidošanās pētniecībā. Pētījumā ne tikai izmantoti iegūtie …