Search results for " white LED"
showing 8 items of 8 documents
Ce:YAG-PMMA nanocomposite for white LED
2012
Ce:YAG-PMMA composite was prepared by a melt compounding method. The characterization was performed using transmission electron microscopy, X-ray diffractometry, and photoluminescence spectroscopy. Results showed that Ce:YAG particles are well dispersed in the polymeric matrix. The luminescence properties of the nanocomposite do not show quenching or significant spectral shift indicating that the nanocomposite can be useful for advanced applications such as white LED construction.
Ce:YAG composites for white LED
2015
Composites and luminescent polymers have been recently found to be potential candidates for the development of white LED, lasers and luminescent concentrators for solar cells. Due to its luminescence properties YAG doped with lanthanides ions is a good candidate as light emitting filler. In a recent our work, the preparation of a polymeric nanocomposite containing Ce:YAG nanoparticles using in situ polymerization has been reported [1]. A good dispersion of Ce:YAG nanoparticles has been obtained maintaining them luminescence properties. In addition, an increase of thermal stability and stiffness of PMMA was observed [2]. Then, the preparation of Ce:YAG-PMMA composite has been performed by us…
Polymeric Ce:YAG nanocomposites: synthesis and characterization
2015
These last years, the development of hybrid polymer-inorganic nanocomposites has been attracted much attention. In particular, composites containing lanthanide-doped materials as filler are candidates for the development of light emitting diodes, lasers and solar cells. Polymers such as polymethylmethacrylate (PMMA), polycarbonate (PC) and polyurethane (PU) are adequate matrices because their good transmission over the visible spectral range, excellent mechanical properties of plasticity, lightness, easiness of fabrication and low cost of mass production. Yttrium aluminum garnet (YAG) doped with Ce(III) ions is one of the yellow phosphor used in the major commercial white LED combined with …
Ce:YAG nanoparticles embedded in a PMMA matrix: preparation and characterization
2010
A Ce:YAG-poly(methyl methacrylate) composite was prepared using in situ polymerization by embedding the Ce:YAG nanopowder in a blend of methyl methacrylate (MMA) and 2-methacrylic acid (MAA) monomers and activating the photopolymerization using a radical initiator. The obtained nanocomposite was yellow and transparent. Its characterization was performed using transmission electron microscopy, small angle X-ray scattering, (13)C cross-polarization magic-angle spinning nuclear magnetic resonance, and photoluminescence spectroscopy. Results showed that Ce:YAG nanoparticles are well dispersed in the polymeric matrix whose structure is organized in a lamellar shape. The luminescence properties o…
Stability improvement of PMMA and Lumogen® coatings for hybrid white LEDs
2014
Hybrid white LEDs employing perylene-based dyes for the frequency down-conversion of blue light, generated by a standard inorganic source, suffer from colour rendering variations due to the degradation of the organic molecule under prolonged irradiation. To avoid such inconvenient, proper encapsulation of the dyes in resins or other polymer matrices can prevent their accelerated ageing; nevertheless, embedding polymers can also exhibit significant bleaching caused by chemico-physical agents. Among all, polymethyl methacrilate (PMMA) is one of the most used materials for the fabrication of hybrid LEDs' colour conversion coatings, therefore its stability needs to be investigated.
Warm white LED light by frequency down- conversion of mixed perylene-based dyes
2013
The growing demand of the solid-state lighting market for the development of sources for illumination has led to the fabrication of the first white LED in 1997, which employed a blue LED coated by a Ce:YAG phosphor to mix the down-converted yellow light with the blue one. The white light appears cold due to the weakness of red 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 efficacy of warm white LEDs is the mai…
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…