Browsing by Subject "High quantum efficiency"

Now showing 1 - 4 of 4

Open Access
High quantum efficiency Type-II superlattice N-structure photodetectors with thin intrinsic layers
(SPIE, 2013) Ergun, Y.; Hostut, M.; Tansel, T.; Muti, bdullah; Kilic, A.; Turan, R.; Aydınlı, Atilla
We report on the development of InAs/AlSb/GaSb based N-structure superlattice pin photodiode. In this new design, AlSb layer in between InAs and GaSb layers acts as an electron barrier that pushes electron and hole wave functions towards the GaSb/InAs interface to perform strong overlap under reverse bias. Experimental results show that, with only 20 periods of intrinsic layers, dark current density and dynamic resistance at -50 mV bias are measured as 6×10-3 A/cm2 and 148 ωcm2 at 77K, respectively. Under zero bias, high spectral response of 1.2A/W is obtained at 5 μm with 50% cut-off wavelengths (λc) of 6 μm. With this new design, devices with only 146 nm thick i-regions exhibit a quantum efficiency of 42% at 3 μm with front-side illimunation and no anti-reflection coatings. © 2013 SPIE.
Open Access
Highly luminescent ZnCdTeS nanocrystals with wide spectral tunability for efficient color-conversion white-light-emitting-diodes
(Institute of Physics Publishing Ltd., 2021-09-28) Soheyli, Ehsan; Zargoush, Sirous; Yazıcı, Ahmet Faruk; Sahraei, Reza; Mutlugün, Evren
CdTe-based semiconductor nanocrystals (NCs) with size and composition-dependent efficient bandgap properties are historically mature nanomaterials for colloidal optoelectronic applications. In this work, we present the highly luminescent quaternary ZnCdTeS NCs with tunable emission across a wide visible spectrum from green to red spectral range. Prepared via a direct aqueous-based approach, a second capping agent of trisodium citrate (TSC) was used to enhance the photoluminescence (PL) emission efficiency, the chemical stability, and to spectrally widen the coverage of the emission spectra of ZnCdTeS NCs. Adding TCS created a remarkable blue shift from 572 nm in the absence of TSC, to 548 nm. On the other hand, upon optimization of experimental parameters, superior ZnCdTeS NCs with a narrow PL profile typically less than 50 nm, the high quantum efficiency of 76%, and tunable emission from 515-to-645 nm were synthesized in an aqueous solvent. The keynotes were the superior and reproducible luminescent properties for the core only NCs, without shell and using relatively low reaction temperatures. It was shown that in the suggested synthesis method, the high efficiency emitted color of ZnCdTeS NCs can be easily controlled from 515-to-650 nm with excellent stability against harsh conditions. The biexponential decay profiles of samples prepared at different reaction temperatures demonstrated that the average recombination lifetime is below 40 ns and increases with the growth of the ZnCdTeS NCs. Results reveal that the excitonic energy levels have the main role in the recombination process. Finally, to demonstrate the functional advantages of the prepared NCs in optoelectronics, the NCs were used to fabricate color-conversion white light-emitting diodes. The color coordinate of the device is recorded as (0.4951, 0.3647) with CRI of 91, CCT of 1954 K, and LER of 251 lm W−1 by employing only two distinct emitters for color conversion.
Open Access
Spectrally tunable white light-emitting diodes based on carbon quantum dot-doped poly(N-vinylcarbazole) composites
(American Chemical Society, 2024-01-26) Sahin Tiras, Kevser; Biçer, Aysenur; Soheyli, Ehsan; Mutlugün, Evren
Electroluminescent white light-emitting diodes (WLEDs) are always of great interest for emerging display applications. Carbon-based quantum dots (CQDs) are the newest emerging nanoscale materials that can be employed for this purpose, owing to their broad and bright light emission properties. In the present work, highly luminescent CQDs with an emission quantum yield of 60% were prepared via a colloidal solvothermal method and subsequent silica gel column chromatography. The photoluminescence (PL) peak was located at 550 nm possessing yellow emission, with a full width at half-maximum of 98 nm and a relatively long lifetime of 10.23 ns through a single-exponential recombination pathway. CQDs were employed in an electroluminescent device architecture of an ITO/PEDOT:PSS/TFB/CQD:PVK/TPBi/LiF/Al structure and blended with poly(N-vinylcarbazole) (PVK) to evaluate their ability to reach white electroluminescent emission. Results confirmed a high external quantum efficiency (EQE) of 0.76% and a maximum luminescence of 774.3 cd·m-2. Tuning the ratio between CQDs and PVK from 1:10.25 to 1:5.75 resulted in a systematic shift in CIE x-y coordinates from 0.23-0.26 to 0.21-0.24, located close to the cool white region. The results of the present study can be considered a step forward in fabricating efficient WLEDs based on low-cost CQDs.
Open Access
Wavelength dependent color conversion of CdSe/ZnS core/shell nanocrystals for white LEDs
(IEEE, 2009) Nizamoğlu, Sedat; Demir, Hilmi Volkan
Nanocrystals (NCs) provide narrow emission spectrum that can be conveniently tuned using quantum size effect. This ability to adjust and control emission spectrum of NCs makes them strong candidates for use in white color conversion light emitting diodes. For example, they are possibly be used for solid state lighting applications including indoor lighting, architectural lighting and scotopic street lighting, where spectrally tuned color conversion is necessary. In device research CdSe/ZnS core/shell nanocrystals are the most commonly used ones because of their good electronic isolation coming from ZnS shells and the resulting high quantum efficiency (QE) (i.e., >50% in solution) [1]. However, when these nanocrystals are integrated into the solid film, e.g., for white light generation, their in-film QE undesirably drops (despite their high QE in solution). Hence, this adversely affects the overall efficiency of the integrating devices that incorporate these NCs [2]. There have been various studies to understand the in-film optical properties of CdSe/ZnS core/shell NCs [3-5]. However, their spectrally resolved in-film quantum efficiency (i.e., the ratio of the number of photons emitted by the nanocrystal film to the number of photons absorbed in the nanocrystal film) and their photon conversion efficiency (i.e., the ratio of the number of photons emitted by the nanocrystal film to the number of photons incident to the nanocrystal film) have not been investigated in these previous studies. © 2009 IEEE.