Color conversion using Quantum Dots on high-brightness GaN LED arrays for display application
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Color conversion using Quantum Dots on high-brightness GaN LED arrays for display application Audrey Sanchot1, Marianne Consonni1, Stéphanie Le Calvez1, Ivan C. Robin1, and François Templier1. 1 Univ. Grenoble Alpes CEA-LETI and 3-5 Lab, MINATEC Campus, 17 rue des martyrs, 38054 Grenoble Cedex 9, France.
ABSTRACT We have demonstrated the color conversion of blue micro-LEDs by means of QDs. In this paper, we will present characterizations that highlight this phenomenon. We already obtained conversion with a complete disappearance of the blue incident signal and a strong color saturation from deep blue (x=0,1626; y=0,0144) to deep red (x=0,6743; y=0,3244). INTRODUCTION Quantum dots [1] (QDs) are small semi conductive organic spheres whose size (few nanometers) shows quantum phenomena. They possess the unique ability to absorb and emit at different wavelengths, depending on their chemical composition and size. Moreover, the full width at half maximum of their emission peak (FWHM) is very narrow (around 30nm). This particularity enables them, when they are incorporated in light sources, to increase color saturation. Finally, they show an interesting quantum emission efficiency. We are interested in using and adapting these properties to generate saturated colors in visualization systems based on LEDs. Although solution processed QDs-based LED already showed quite promising performances [2], electrically excited QDLEDs are quite difficult to obtain and cannot be yet commercialized. Nevertheless, the use of QDs in photoluminescence can already be exploited and considered for industrial applications. Several technical bottlenecks are related to this approach. One is the minimum thickness necessary to convert all the blue light into red or green. Another is to achieve red, green, and blue structuration on small pixel-sizes, which are typically as small as 10μm for micro display applications. In this article, we will present conversions from blue to red with QDs implemented on array of hybridized LEDs. EXPERIMENT QDs are core-shell CdSe/ZnS quantum dots with an emission wavelength at 620nm. They were purchased from Mesolight. QDs were dispersed in chloroform. The solution was then added to a matrix according to the ratio (2:1). More precisely, 200μL of QDs solution was mixed to 100μL of the chosen matrix.
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Optical and electro-optical characterizations are made with photoluminescence, absorption and conversion ratio measurements. Electro-optical performances of QDs are measured with a Keithley 2000 and a Spectra Scan Photo-Research 650. All the measurements are performed at room temperature, in air. The test samples are glass slides of 3x3mm on which the solution is deposited by drop casting. These substrates are then placed on arrays of hybridized blue LEDs arrays [3] as illustrated in Figure 1.
Figure 1: (Left) Layout of the structure; (Right) Array blue emission. For color conversion demonstration, only one blue LED pixel, with a side size of 6.5μm, is switched on. Samples with QDs on it are placed on top, with QDs
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