Browsing by Author "Sapra, S."
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Open Access Multi-layered CdSe/ZnS/CdSe heteronanocrystals to generate and tune white light(2008-11) Nizamoğlu, Sedat; Mutlugün, Evren; Özel, Tuncay; Demir, Hilmi Volkan; Sapra, S.; Gaponik, N.; Eychmüller, A.In this study, tuneable white light generation by controlling CdSe/ZnS/CdSe core/shell/shell heteronanocrystals integrated on InGaN/GaN light emitting diodes was presented. These multilayered quantum dots, also known as onion-like heterostructures, were designed and synthesized to emit in red (around 600 nm) from the CdSe core and in green (around 550 nm) from the CdSe shell. By designing and hybridizing these red-green emitting heterostructures on blue emitting LEDs, an integrated WLEDs on a single chip was demonstrated. By controlling the number of integrated heteronanocrystals, their (x,y) tristimulus coordinates were tuned from (0.26,0.23) to (0.37,0.36), along with their corresponding correlated color temperature tuned from 27413 K to 4192 K and the luminous efficacy of their optical radiation (the ratio of the emitted luminous flux to the radiant flux) tuned from 258 lm/W to 375 lm/W. Further investigation on the change of in-film optical properties of these heteronanocrystals with respect to their in-solution emission was performed.Item Open Access Selective enhancement of surface-state emission and simultaneous quenching of interband transition in white-luminophor CdS nanocrystals using localized plasmon coupling(Institute of Physics Publishing Ltd., 2008) Ozel, T.; Soganci, I. M.; Nizamoglu, S.; Huyal I.O.; Mutlugun, E.; Sapra, S.; Gaponik N.; Eychmüller A.; Demir, Hilmi VolkanWe propose and demonstrate the controlled modification and selective enhancement of surface-state emission in white-luminophor CdS nanocrystals (NCs) by plasmon-coupling them with proximal metal nanostructures. By carefully designing nano-Ag films to match their localized plasmon resonance spectrally with the surface-state emission peak of CdS NCs, we experimentally show that the surface-state emission is substantially enhanced in the visible wavelength, while the interband (band-edge) transition at the shorter wavelength far away from the plasmon resonance is simultaneously significantly suppressed. With such plasmon tuning and consequent strong plasmon coupling specifically for the surface-state transitions, the surface-state emission is made stronger than the band-edge emission. This corresponds to an enhancement factor of 12.7-fold in the ratio of the surface-state peak emission to the band-edge peak emission of the plasmon-coupled film sample compared with that in solution. Such a plasmonic engineering of surface-state emission in trap-rich CdS white nanoluminophors holds great promise for future solid-state lighting.Item Open Access Surface-state emission enhancement in white-luminophor CdS nanocrystals using localized plasmon coupling(IEEE, 2008-11) Özel, Tuncay; Soğancı, İbrahim Murat; Nizamoğlu, Sedat; Huyal, İlkem Özge; Mutlugün, Evren; Sapra, S.; Gaponik, N.; Eychmüller, A.; Demir, Hilmi VolkanTo make surface-state emission stronger than band-edge emission for the first time, we proposed and demonstrated plasmon coupling of the surface-state emission from the traps in these CdS nano-luminophors using localized plasmons.Item Open Access Tuning shades of white light with multi-color quantum-dot-quantum-well emitters based on onion-like CdSe-ZnS heteronanocrystals(Institute of Physics Publishing Ltd., 2008) Demir, Hilmi Volkan; Nizamoglu, S.; Mutlugun, E.; Ozel, T.; Sapra, S.; Gaponik N.; Eychmüller A.We present white light generation controlled and tuned by multi-color quantum-dot-quantum-well emitters made of onion-like CdSe/ZnS/CdSe core/shell/shell heteronanocrystals integrated on InGaN/GaN light-emitting diodes (LEDs). We demonstrate hybrid white LEDs with (x, y) tristimulus coordinates tuned from (0.26, 0.33) to (0.37, 0.36) and correlated color temperatures from 27 413 to 4192 K by controlling the number of their integrated red-green-emitting heteronanocrystals. We investigate the modification of in-film emission from these multi-layered heteronanocrystals with respect to their in-solution emission, which plays a significant role in hybrid LED applications. Our proof-of-principle experiments indicate that these complex heteronanocrystals hold promise for use as nanoluminophors in future hybrid white LEDs.Item Open Access White CdS nanoluminophore based tunable hybrid light emitting diodes(IEEE, 2007) Nizamoğlu, Sedat; Mutlugün, Evren; Akyüz, Özgün; Kosku-Perkgöz, Nihan; Demir, Hilmi Volkan; Liebscher, L.; Sapra, S.; Gaponik, N.; Eychmüller, A.The study aims to fabricate and demonstrate hybrid white light emitting diodes that integrate white emitting CdS nanoluminophores with high light quality. Results show that the white light properties of these hybrid WLED (including (x,y) chromaticity coordinates, color temperature, and color rendering index (Ra)) are conveniently tuned as desired across the white region by controlling the number of these surface state emitting nanoluminophores hybridized on the n-UV LED platform. In this tuning process, with the increasing number of the hybridized surface state emitting nanocrystals, it is observed that (x,y) and Ra increase while Tc decreases.Item Open Access White emitting CdS quantum dot nanoluminophores hybridized on near-ultraviolet LEDs for high-quality white light generation and tuning(Institute of Physics Publishing Ltd., 2008) Nizamoglu, S.; Mutlugun, E.; Akyuz, O.; Perkgoz, N. K.; Demir, Hilmi Volkan; Liebscher, L.; Sapra, S.; Gaponik N.; Eychmüller A.To generate white light using semiconductor nanocrystal (NC) quantum dots integrated on light emitting diodes (LEDs), multiple hybrid device parameters (emission wavelengths of the NCs and the excitation platform, order of the NCs with different sizes, amount of the different types of NCs, etc) need to be carefully designed and properly implemented. In this study, we introduce and demonstrate white LEDs based on simple device hybridization using only a single type of white emitting CdS quantum dot nanoluminophores on near-ultraviolet LEDs. Here we present their design, synthesis-growth, fabrication and characterization. With these hybrid devices, we achieve high color rendering index (>70), despite using only a single NC type. Furthermore, we conveniently tune their photometric properties including the chromaticity coordinates, correlated color temperature, and color rendering index with the number of hybridized nanoluminophores in a controlled manner.