Browsing by Subject "Emission spectrums"

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    Alloyed heterostructures of CdSexS1-x nanoplatelets with highly tunable optical gain performance
    (American Chemical Society, 2017) Kelestemur Y.; Dede, D.; Gungor K.; Usanmaz, C. F.; Erdem, O.; Demir, Hilmi Volkan
    Here, we designed and synthesized alloyed heterostructures of CdSexS1-x nanoplatelets (NPLs) using CdS coating in the lateral and vertical directions for the achievement of highly tunable optical gain performance. By using homogeneously alloyed CdSexS1-x core NPLs as a seed, we prepared CdSexS1-x/CdS core/crown NPLs, where CdS crown region is extended only in the lateral direction. With the sidewall passivation around inner CdSexS1-x cores, we achieved enhanced photoluminescence quantum yield (PL-QY) (reaching 60%), together with increased absorption cross-section and improved stability without changing the emission spectrum of CdSexS1-x alloyed core NPLs. In addition, we further extended the spectral tunability of these solution-processed NPLs with the synthesis of CdSexS1-x/CdS core/shell NPLs. Depending on the sulfur composition of the CdSexS1-x core and thickness of the CdS shell, CdSexS1-x/CdS core/shell NPLs possessed highly tunable emission characteristics within the spectral range of 560-650 nm. Finally, we studied the optical gain performances of different heterostructures of CdSexS1-x alloyed NPLs offering great advantages, including reduced reabsorption and spectrally tunable optical gain range. Despite their decreased PL-QY and reduced absorption cross-section upon increasing the sulfur composition, CdSexS1-x based NPLs exhibit highly tunable amplified spontaneous emission performance together with low gain thresholds down to ∼53 μJ/cm2.
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    Laser action studies of π-conjugated polymer microcavities
    (IEEE, 2008) Tülek, Abdullah; Vardeny, Z. V.
    Unidirectional laser emission was observed from φ-conjugated polymer microcavities with spiral geometry, and from microdisks containing line defects. For both type of cavities directionality contrast of the laser emission was found to be ̃ 10, with far-field lateral divergence angle of ̃ 15°. No significant increase in the laser threshold intensity was observed compared with simple microdisk cavities. In addition we also studied the emission spectra of microring polymer lasers fabricated on nylon microfibers upon application of uniaxial stress with strain up to ̃ 12%. Substantial change in the laser emission spectrum was observed when stress was applied; showing enhanced optical sensitivity to stress larger than the changes induced in the emission spectrum caused by the microfiber diameter change. We explain the enhanced sensitivity to stress as due to the induced change in the polymer refractive index dispersion, in particular at the laser emission wavelength (̃ 635 nm).
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    Ultralow threshold laser action from toroidal polymer microcavity
    (American Institute of Phycsics, 2009) Tulek, A.; Akbulut, D.; Bayındır, Mehmet
    We report laser action from a toroidal microcavity coated with π-conjugated polymer. An ultralow threshold value of ∼200 pJ/pulse is achieved by free space excitation in ambient conditions. This is the lowest threshold energy obtained in microtoroid lasers by free space excitation. The effective refractive index of the polymer, extracted from Fourier analysis of emission spectra, is 1.787, which is very close to measured value of 1.790 indicating that laser modes are located around the circumference of the cavity as whispering gallery resonances. © 2009 American Institute of Physics.
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    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.