Linear and Two-Photon Absorption in Zero- and One-Dimensional CdS Nanocrystals: Influence of Size and Shape

Achtstein, Alexander W.; Hennig, Jonas; Prudnikau, Anatol; Artemyev, Mikhail; Woggon, U.

doi:10.1021/jp407453e

Cited by 30 publications

(70 citation statements)

References 28 publications

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“…A TPA local field model analogue to above using CdS bulk material TPA coefficients 36 shows good agreement with the experimental data. 17 (Data of Li et al 31 show the same trend but may be displaced a bit to lower values due to a different concentration determination method).…”

Section: Nano Lettersmentioning

confidence: 84%

“…The effect is not as pronounced for 1D NRs and 0D QDs, where for QDs an enhancement of the TPA cross sections for strongly confined nanoparticles has been observed. 17 Moreover, the theoretical results of Feng et al 16 in Figure 6 show that confinement generally leads to an enhancement of the TPA cross sections with respect to the bulk TPA local field scaling.…”

Section: Nano Lettersmentioning

confidence: 96%

“…Green (2P-PLE) and blue (z-scan) dots show our experimental results. Gray dotted curves are results from TPA local field theory in analogy to Blanton 36 and Achtstein et al 17 for zinc blende CdSe for differently anisotropic particles, where L y /L x = 1 represents a perfect sphere or platelets with identical lateral extensions and L y /L x < 1, e.g., NPLs of nonidentical lateral extensions. Experimental results from Pu et al 44 an effect merely resulting from the linear absorption cross section for the observed shape dependent behavior of the TPA cross sections we plot σ (2) (800 nm)/σ (1) (400 nm) over the aspect ratio in Figure 8.…”

Section: Nano Lettersmentioning

confidence: 99%

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Two Photon Absorption in II–VI Semiconductors: The Influence of Dimensionality and Size

et al. 2015

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We report a comprehensive study on the two-photon absorption cross sections of colloidal CdSe nanoplatelets, -rods, and -dots of different sizes by the means of z-scan and two-photon excitation spectroscopy. Platelets combine large particle volumes with ultra strong confinement. In contrast to weakly confined nanocrystals, the TPA cross sections of CdSe nanoplatelets scale superlinearly with volume (V(∼2)) and show ten times more efficient two-photon absorption than nanorods or dots. This unexpectedly strong shape dependence goes well beyond the effect of local fields. The larger the particles' aspect ratio, the greater is the confinement related electronic contribution to the increased two-photon absorption. Both electronic confinement and local field effects favor the platelets and make them unique two-photon absorbers with outstanding cross sections of up to 10(7) GM, the largest ever reported for (colloidal) semiconductor nanocrystals and ideally suited for two-photon imaging and nonlinear optoelectronics. The obtained results are confirmed by two independent techniques as well as a new self-referencing method.

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Section: Nano Lettersmentioning

confidence: 84%

Section: Nano Lettersmentioning

confidence: 96%

Section: Nano Lettersmentioning

confidence: 99%

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Two Photon Absorption in II–VI Semiconductors: The Influence of Dimensionality and Size

et al. 2015

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“…Our applied local field theory has already proved applicability for describing dielectric effects in the continuum absorption of CdSe, CdS, and PbSe nanodots and nanorods. 5,7,23 Because μ i (E) = δ (1) (E)/V P (with the particle volume V P ) is valid, it is possible to calculate the intrinsic absorption μ i for randomly oriented nanoplatelets (dots, rods) according to eq 3 by numerical integration of eq 5. Figure 2 shows the obtained aspect ratio dependence of μ i at 4 eV for zinc blende (ZB) CdSe particles (with lateral aspect ratio R = 1, e.g., symmetric platelets and R < 1, e.g., asymmetric platelets) using bulk dielectric function data for CdSe 33 and our solvent chloroform 32 for our colloidal dispersion of randomly oriented particles.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Linear Absorption in CdSe Nanoplates: Thickness and Lateral Size Dependency of the Intrinsic Absorption

et al. 2015

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We investigate the optical absorption properties of colloidal CdSe nanoplatelets and compare them to CdSe quantum dots. Starting from inductively coupled plasma−atomic emission spectroscopy (ICP-AES) measurements on their intrinsic absorption coefficients μ i , we compare these results with a theoretical approach by a continuum absorption Lorentz local field model. We show that the platelets' intrinsic absorption coefficients μ i are strongly thickness and aspect ratio dependent, which results in the possibility to tune the absorption properties of this material class by the lateral size and thickness. The continuum intrinsic absorbance of the platelets is considerably larger if compared with quantum dots making them more efficient absorbers with higher light−matter interaction that is essential for their use in, for example, solar cells. The obtained μ i values can be used for concentration determination of CdSe nanoplatelets in solution and solid films which is essential for all optical experiments with controlled generated population density upon optical excitation. ■ INTRODUCTIONIn recent years, the influence of size and shape on the linear absorption properties of semiconductor nanoparticles has gained growing interest with respect to nanoparticles in dispersion or polymeric matrices. Recent investigations 1−6 have shown that the absorption properties of II−VI semiconductor nanoparticles can be strongly altered not only by the electronic and dielectric carrier confinement but also by the dielectric environment of these particles. This is because the light−matter interaction (e.g., absorption or emission of radiation) is connected to local fields inside the nanoparticles and the effective medium dielectric constant. 7 Different kinds of CdSe, CdS, PbS, and PbSe 1−6,8,9 particles in the shape of dots, rods, and wires were investigated. They exhibited a strong shape, aspect ratio, and dielectric contrast (semiconductor vs surrounding medium) dependence of their optical properties such as a shape dependent intrinsic absorption coefficient, polarized emission and absorption, and a varying oscillator strength and exciton lifetime. 2,7 In recent years, a new class of colloidal nanoparticles has been synthesized, the colloidal II−VI nanoplatelets (NPLs). 10−13 These ultrathin and flat nanocrystals (made of CdSe, CdS, or CdTe) exhibit lateral dimensions of the order of tens of nanometers and thicknesses of several monolayers. 10−12,14−19 Strong anisotropic quantum confinement in the NPLs results in spectrally narrow absorption and photoluminescence peaks even at room temperature. Because lateral dimensions of NPLs are much larger than their thicknesses, NPLs can be considered as the colloidal analogue of ultrathin semiconductor quantum wells (QWs) prepared by molecular beam epitaxy (MBE). 20,21 For many, for example, optical investigations, linear absorption cross sections or intrinsic absorption coefficients are necessary to determine the absolute particle concentrations of nanoparticles in colloidal solutions. Ther...

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“…Indeed, measurements of TPA cross sections of various QDs are often performed for a single wavelength only that does not necessarily correspond to the maximum of the TPA band, and the reports lack the confrontation of the obtained values with the quantum yield (QY) of the TPEE, which is a crucial parameter in microscopy imaging applications. Additionally, most of the work have been conducted for cadmium-based QDs, [5][6][7] with inherent cytotoxicity and thus limited applications in biological and biomedical areas. 8 An interesting alternative for II-IV type QDs is less harmful, types III-V semiconductor materials.…”

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Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

et al. 2015

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Linear and Two-Photon Absorption in Zero- and One-Dimensional CdS Nanocrystals: Influence of Size and Shape

Cited by 30 publications

References 28 publications

Two Photon Absorption in II–VI Semiconductors: The Influence of Dimensionality and Size

Two Photon Absorption in II–VI Semiconductors: The Influence of Dimensionality and Size

Linear Absorption in CdSe Nanoplates: Thickness and Lateral Size Dependency of the Intrinsic Absorption

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

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