Browsing by Subject "Nanocrystal quantum dots"

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Open Access
Continuously tunable emission in inverted type ‐ I CdS/CdSe core/crown semiconductor nanoplatelets
(Wiley, 2015-07-15) Delikanlı, S.; Güzeltürk, B.; Hernandez - Martinez, P. L.; Erdem, T.; Keleştemur, Y.; Olutas M.; Akgül, M. Z.; Demir, Hilmi Volkan
The synthesis and unique tunable optical properties of core/crown nanoplatelets having an inverted Type-I heterostructure are presented. Here, colloidal 2D CdS/CdSe heteronanoplatelets are grown with thickness of four monolayers using seed-mediated method. In this work, it is shown that the emission peak of the resulting CdS/CdSe heteronanoplatelets can be continuously spectrally tuned between the peak emission wavelengths of the core only CdS nanoplatelets (421 nm) and CdSe nanoplatelets (515 nm) having the same vertical thickness. In these inverted Type-I nanoplatelets, the unique continuous tunable emission is enabled by adjusting the lateral width of the CdSe crown, having a narrower bandgap, around the core CdS nanoplatelet, having a wider bandgap, as a result of the controlled lateral quantum confinement in the crown region additional to the pure vertical confinement. As a proof-of-concept demonstration, a white light generation is shown by using color conversion with these CdS/CdSe heteronanoplatelets having finely tuned thin crowns, resulting in a color rendering index of 80. The robust control of the electronic structure in such inverted Type-I heteronanoplatelets achieved by tailoring the lateral extent of the crown coating around the core template presents a new enabling pathway for bandgap engineering in solution-processed quantum wells.
Open Access
Large-area (> 50 cm × 50 cm), freestanding, flexible, optical membranes of Cd-free nanocrystal quantum dots
(IEEE, 2012) Mutlugün, Evren; Hernandez Martinez, Pedro L.; Eroğlu, Cüneyt; Coşkun, Yasemin; Erdem, Talha; Sharma, Vijay K.; Ünal, Emre; Panda, S. K.; Hickey, S. G.; Gaponik, N.; Eychmuller, A.; Demir, Hilmi Volkan
Colloidal semiconductor quantum dots (QDs) have been extensively explored for numerous applications ranging from optoelectronics to biotechnology. This strong demand for the colloidal QDs arises because of their favorable optical and electronic properties. From the application points of view, QDs typically need to be used in their solid form, as opposed to their as-synthesized dispersion form. For immobilization of QDs and homogeneity of their films, various polymers have been used to host QDs within solid media. However, the integration of QDs into a polymeric medium is commonly complex, which requires a high level of understanding to provide optical quality. © 2012 IEEE.
Open Access
Quantum dot integrated LEDs using photonic and excitonic color conversion
(Elsevier, 2011-11-23) Demir, Hilmi Volkan; Nizamoglu, S.; Erdem, T.; Mutlugun, E.; Gaponik N.; Eychmüller A.
This review summarizes advantages, recent progress and challenges related to the quickly evolving research field of colloidal quantum dot integrated LEDs based on color conversion. We start with presenting a short general introduction to the field of solid state lighting and color conversion phenomena, which are essential for defining the requirements for high-quality general lighting. Subsequently we continue with a brief description of the synthesis of nanocrystal quantum dots and their optical properties together with the advantages of utilizing them in LEDs as color convertors. Following this basic background, we review the recent efforts on quantum dot integrated color-conversion LEDs, Förster resonance energy transfer (FRET) converted LEDs and FRET-enhanced LEDs. Finally, we conclude with a future outlook on semiconductor lighting and quantum dot integrated LEDs.
Open Access
Warm-White light-Emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering: Reply to comment
(2011) Nizamoglu, S.; Erdem, T.; Sun X.W.; Demir, Hilmi Volkan
The correlated color temperatures and the corresponding color rendering indices calculated using actual experimental data (and not any prediction) in the original Letter [Opt. Lett. 35, 3372 (2010)] are correct. In addition, here the color rendering of our white LEDs integrated with nanocrystal quantum dots (NQDs) is provided for all test samples. Also, a new NQD-LED design with both high luminous efficacy of optical radiation and CRI is presented to have a chromaticity point in the quadrangle stated in the comment Letter [Opt. Lett. 36, 2851 (2011)]. The points made in the original Letter and all the calculation results provided therein are valid. © 2011 Optical Society of America.