Optical and Dynamic Properties of Undoped and Doped Semiconductor Nanostructures

Grant, Christian D.; Zhang, J Z

doi:10.1142/9789812790248_0001

Cited by 21 publications

(6 citation statements)

References 297 publications

(398 reference statements)

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“…The former is due to the electronic transition from the bottom of the conduction band to the top of the valence band with the subsequent radiative band-edge recombination, while the latter results from nonradiative relaxation pathways related to the surface or internal defects. Trap states are typically located within the QD semiconductor bandgap, and hence their emission is usually red-shifted concerning the band-edge emission. − This indicates that surface or interfacial trap states created by QD surface modification may contribute (at least partially) to the emission wavelength red shift observed in the PL data of the irradiated QD samples CdTe-537 and CdTe-546 (Figures c,d and c,d). Indeed, the hydrophilic surfaces of thiol-capped QDs may become imperfect under laser irradiation by losing thiol ligands via photooxidation, which would produce more defects on QD surfaces, resulting in increased nonradiative decay (trap-state emission), decreased PL intensity (photobleaching), and shortened PL lifetime .…”

Section: Results and Discussionmentioning

confidence: 99%

Size-Dependent Photobleaching Mechanism and Kinetics Induced by Nanosecond Laser Pulses in Colloidal Semiconductor Quantum Dots

et al. 2022

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An experimental-theoretical approach is proposed to investigate the size-dependent photobleaching of colloidal semiconductor quantum dots (QDs) excited by a nanosecond pulsed laser. In the experimental background, the ground-state absorption and photoluminescence (PL) spectra of chemically prepared QDs are monitored over an excitation time at distinct laser irradiances. The magnitude of photobleaching in the QD solution is quantified by the decay rate of the PL signal as a function of the excitation time and the laser power. A theoretical spectroscopy model is then used to estimate the particle size distribution (PSD) in colloidal solution from the absorption data generated at different laser powers. The resulting evolution of the PSD of the QD ensemble under irradiation is analyzed in terms of classical crystallization theories dealing with the formation, growth, and dissolution of colloidal particles in a supersaturated medium. The QD response to laser irradiation is also interpreted by a simple mechanical model that correlates the photoinduced hydrostatic strain at the solid/liquid interface and the predicted variation of the mean particle size. The reported experimental and theoretical methods are used to completely elucidate the basic physico-chemical processes responsible for the laser-induced photobleaching kinetics of glutathione-capped CdTe aqueous QDs with very small mean sizes. For this purpose, we synthesized a series of colloidal QD samples with mean particle diameters ranging from 1.95 to 2.68 nm. Our results indicate that a faster photobleaching rate occurs in QD samples with smaller sizes in which particle dissolution under laser irradiation is predominant. On the other hand, the photobleaching rate becomes slower in samples with larger dot sizes, possibly due to the formation of core/shell structures in solution via thermal degradation of thiol ligands either during the chemical synthesis or as a consequence of the subsequent interaction with the excitation laser.

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Section: Results and Discussionmentioning

confidence: 99%

Size-Dependent Photobleaching Mechanism and Kinetics Induced by Nanosecond Laser Pulses in Colloidal Semiconductor Quantum Dots

et al. 2022

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“…On the other hand, the methods commonly adopted for particle sizing (AFM and TEM), while remarkably useful, require a careful and crucial sample preparation process in which the nanocrystals are deposited on a suitable substrate. In addition to the high cost of the basic equipment for both TEM and AFM, the statistical data generated during the size analysis is based on a limited amount of particles so that a good representativeness of the measured ensemble is laboriously achieved. − Dynamic light scattering (DLS) can also be used to determine the size distribution of nanocrystals directly in solution. Such a technique is sensitive to a wide range of parameters, which may compromise the accuracy of the measured distribution.…”

Section: Introductionmentioning

confidence: 99%

Combined Theoretical–Experimental Approach to the Growth Kinetics of Colloidal Semiconductor Nanocrystals

Ferreira

Silva

et al. 2019

J. Phys. Chem. C

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A new theoretical analytical model is proposed in order to provide a quantitative description of the growth kinetics of colloidal semiconductor nanocrystals. The temporal evolution of the mean size of the nanocrystal ensemble in solution was determined by monitoring the variation of the absorption and photoluminescence spectra in the course of the chemical synthesis and then submitting the resulting optical data to a calculation procedure that generated the corresponding time-evolving particle size distribution. Two main problems were addressed and properly correlated: the size-dependence of the bandgap transition for a single semiconductor nanocrystal, which was treated within the framework of the finite-depth square-well effective mass approximation, and the inhomogeneous broadening of the optical spectra due to the distribution of nanocrystal sizes and hence the distribution of bandgaps. By application of the reported methodology to CdTe nanocrystals synthesized through a one-pot aqueous chemical route, growth curves (mean particle size as a function of time) were calculated for syntheses performed under various initial experimental conditions. Such kinetic results were interpreted in the sense of the well-established classical crystallization theories based on homogeneous nucleation and growth of spherical particles in solution, including a detailed study on the Ostwald ripening process. Specific growth modes were identified along with numerical estimates for their characteristic rate constants. The presented calculation method is easy to implement, and it can be used to access the size evolution of solution-grown nanocrystals of many other semiconductor materials, regardless of the adopted preparation procedure.

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“…Semiconductor QDs have rich optical properties that strongly depend on size, especially when the particle size is less than the exciton Bohr radius of the material [4,5]. The electrical and optical properties of group III nitride materials are of great interest for light-emitting diodes (LEDs), lasers and other optoelectronic devices because of their band structures and the large range of band gap (0.7-6.2 eV) .…”

Section: Introductionmentioning

confidence: 99%

Electroluminescence from GaN Nanostructures

Keno¹,

Melese²,

Choudary³

2015

ujpa

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Electroluminescence (EL) intensity from GaN nanostructures is reported as a function of different parameters, such excitation wavelength, number of the nanostructures, applied voltage, temperature and time. Quantum confinement model (QCM) is used to develop the model equation that describes the EL intensity as a function of size of the nanostructures. It is shown that as the number of nanostructures decreases EL intensity increases. The highly efficient EL intensity is obtained at low operating voltage (6V). It is observed that EL intensity decreases as the temperature increases and degrades with time.

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Optical and Dynamic Properties of Undoped and Doped Semiconductor Nanostructures

Cited by 21 publications

References 297 publications

Size-Dependent Photobleaching Mechanism and Kinetics Induced by Nanosecond Laser Pulses in Colloidal Semiconductor Quantum Dots

Size-Dependent Photobleaching Mechanism and Kinetics Induced by Nanosecond Laser Pulses in Colloidal Semiconductor Quantum Dots

Combined Theoretical–Experimental Approach to the Growth Kinetics of Colloidal Semiconductor Nanocrystals

Electroluminescence from GaN Nanostructures

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