Browsing by Subject "High color rendering index"

Now showing 1 - 6 of 6

Open Access
High-quality InP/ZnS nanocrystals with high photometric performance and their application to white quantum dot light-emitting diodes
(IEEE, 2012) Yang, X.; Tan, S. T.; Demir, Hilmi Volkan; Sun, X. W.
Full visible range covering InP/ZnS core-shell nanocrystals with high photometric performance have been prepared. Making use of these nanocrystals, we demonstrate a white quantum dot LED with a high color rendering index of 91. © 2012 IEEE.
Open Access
Implementation of high-quality warm-white light-emitting diodes by a model-experimental feedback approach using quantum dot-salt mixed crystals
(American Chemical Society, 2015) Adam, M.; Erdem, T.; Stachowski, G.M.; Soran-Erdem Z.; Lox, J. F. L.; Bauer, C.; Poppe, J.; Demir, Hilmi Volkan; Gaponik N.; Eychmüller A.
In this work, a model-experimental feedback approach is developed and applied to fabricate high-quality, warm-white light-emitting diodes based on quantum dots (QDs) as color-conversion materials. Owing to their unique chemical and physical properties, QDs offer huge potential for lighting applications. Nevertheless, both emission stability and processability of the QDs are limited upon usage from solution. Incorporating them into a solid ionic matrix overcomes both of these drawbacks, while preserving the initial optical properties. Here borax (Na2B4O7·10H2O) is used as a host matrix because of its lower solubility and thereby reduced ionic strength in water in comparison with NaCl. This guarantees the stability of high-quality CdSe/ZnS QDs in the aqueous phase during crystallization and results in a 3.4 times higher loading amount of QDs within the borax crystals compared to NaCl. All steps from the synthesis via mixed crystal preparation to the warm-white LED preparation are verified by applying the model-experimental feedback, in which experimental data and numerical results provide feedback to each other recursively. These measures are taken to ensure a high luminous efficacy of optical radiation (LER) and a high color rendering index (CRI) of the final device as well as a correlated color temperature (CCT) comparable to an incandescent bulb. By doing so, a warm-white LED with a LER of 341 lm/Wopt, a CCT of 2720 K and a CRI of 91.1 is produced. Finally, we show that the emission stability of the QDs within the borax crystals on LEDs driven at high currents is significantly improved. These findings indicate that the proposed warm-white light-emitting diodes based on QDs-in-borax hold great promise for quality lighting. © 2015 American Chemical Society.
Open Access
Synthesis of fluorescent core-shell nanomaterials and strategies to generate white light
(American Institute of Physics Inc., 2015) Singh, A.; Kaur, R.; Pandey, O. P.; Wei, X.; Sharma, M.
In this work, cadmium free core-shell ZnS:X/ZnS (X-=-Mn, Cu) nanoparticles have been synthesized and used for white light generation. First, the doping concentration of Manganese (Mn) was varied from 1% to 4% to optimize the dopant related emission and its optimal value was found to be 1%. Then, ZnS shell was grown over ZnS:Mn(1%) core to passivate the surface defects. Similarly, the optimal concentration of Copper (Cu) was found to be 0.8% in the range varied from 0.6% to 1.2%. In order to obtain an emission in the whole visible spectrum, dual doping of Mn and Cu was done in the core and the shell, respectively. A solid-solid mixing in different ratios of separately doped quantum dots (QDs) emitting in the blue green and the orange region was performed. Results show that the optimum mixture of QDs excited at 300-nm gives Commission Internationale del'Éclairage color coordinates of (0.35, 0.36), high color rendering index of 88, and correlated color temperature of 4704-K with minimum self-absorption. © 2015 AIP Publishing LLC.
Open Access
Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering
(2010) Nizamoglu, S.; Erdem, T.; Sun X.W.; Demir, Hilmi Volkan
Warm-white LEDs (WLEDs) with high spectral quality and efficiency are required for lighting applications, but current experimental performances are limited. We report on nanocrystal quantum dot (NQD) hybridized WLEDs with high performance that exhibit a high luminous efficacy of optical radiation exceeding 350 lm/Wopt and a high color rendering index close to 90 at a low correlated color temperature <3000 K. These spectrally engineered WLEDs are obtained using a combination of CdSe/ZnS core/shell NQD nanophosphors integrated on blue InGaN/GaN LEDs. © 2010 Optical Society of America.
Open Access
White light generating semiconductor nanocrystal luminophors with high photometric quality
(IEEE, 2008-12) Demir, Hilmi Volkan
We proposed and demonstrated warm white light generating combinations of semiconductor nanocrystal quantum dot emitters with high photometric quality including high color rendering index (~80) on LED platforms to meet requirements of future lighting. Additionally, we developed and demonstrated plasmon coupling of these nanocrystal luminophors with metal nanoparticles to control and enhance their spontaneous emission in the solid state film.
Open Access
White light generation with azide functionalized polyfluorene hybridized on near-UV light emitting diode
(OSA, 2007) Hüyal, İlkem Özge; Özel, Tuncay; Nizamoğlu, Sedat; Koldemir, Ünsal; Tuncel, Dönüş; Demir, Hilmi Volkan
We present white light generation using poly[(9,9-dihexylfluorene)-co-alt- (9,9-bis-(6- azidohexyl)fluorene] (PFA) for the first time. Hybridizing PFA on near-UV LED, we demonstrate high color rendering index up to 91.0.