Photoluminescence properties of Eu3+-doped Cd1−x Zn x S quantum dots (original) (raw)
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Photo-physical Properties of Cd (1-x)-y Zn x Fe y S Nanocrystals
Polyvinyl pyrrolidone capped Cd (1-x)-y Zn x Fe y S [(0≤x≤0.5); (0.0001≤y≤0.1)] nanocrystals have been synthesized using aqueous chemical coprecipitation method. Crystallographic characterization of synthesized quaternary semiconductor compounds have been done using X-ray diffraction (XRD), average crystallite size calculated from the recorded XRD patterns is ~3.5nm. Time resolved luminescence spectra have been recorded using high peak power, pulsed N 2-laser excitation for photo-physical behaviour analysis of synthesized nanocrystals. Decay time values have been calculated from recorded multi-exponential luminescence decay curves using Bube's peeling off method, all the observed decay time values lie in µs time domain. Decay time dependence on dopant concentration has been studied in detail.
Highly Luminescent Cd1−xZnxSe/ZnS Core/Shell Nanocrystals Emitting in the Blue–Green Spectral Range
Small, 2007
Recent developments in the field of the synthesis of semiconductor nanocrystals aim at the use of easy-to-manipulate, inexpensive, and environmentally benign precursors and solvents, necessary for an industrial up-scaling of the process. Such "green-chemical" methods have been reported, for example, for the preparation of CdSe, CdS, CdTe, ZnSe, and InP nanocrystals. [1-6] These binary systems are, however, not very appropriate for emission in the spectral region from 480 to 550 nm. In particular the wavelength range of 525-535 nm is of technological interest for the preparation of nanocrystal-based green LEDs and white-light generation. Cd 1Àx Zn x Se alloy nanocrystals are an attractive alternative as here the emission color can be tuned from the UV/ blue spectral region (ZnSe) to the visible one (CdSe) by changing the composition, that is, the Cd:Zn ratio, without changing the nanocrystal size. [7, 8] In this Communication, we describe a fast method for the preparation of nearly monodisperse Cd 1Àx Zn x Se nanocrystals as well as their passivation with a ZnS shell without the use of pyrophoric organometallic precursors. Diethylzinc and dimethylcadmium used in the literature [7] were replaced by the air-stable compounds zinc stearate and cadmium stearate, respectively, and TOPO by a solvent mixture of octadecene and oleylamine. After placing the Se precursor (TOPSe) into the hot solvent, the reaction could be carried out in three ways: 1) Injection of the cadmium precursor followed by injection of the zinc precursor (CdSe-seeded growth), 2) injection in the reverse order (ZnSe-seeded growth), or 3) simultaneous injection of both precursors. Using method 1, formation of CdSe nanocrystals took place accompanied by a steady red shift of the excitonic and the photoluminescence (PL) peak. Energy dispersive X-ray (EDX) analysis indicated that subsequent incorporation of
Zn1-xCdxO (x=0, 0.02, 0.04, 0.06) nanoparticles have been synthesized by sol-gel method. X-ray diffraction studies revealed that the powders possess Hexagonal Wurtzite phase. Rietveld refinement showed a significant change in lattice parameters of Zn1-xCdxO compounds with cadmium concentration. The optical band gap, estimated from Ultraviolet-Visible Spectroscopy study, decreased from 3.22 to 3.15 eV with the increase in cadmium content. The photoluminescence spectrum exhibited three different emission bands around 410 nm, 460 nm and 510 nm. The broadness of strong green emission peak was observed to increase with cadmium concentration. All the luminescence peaks are explained as due to various defects like zinc vacancy (VZn), oxygen vacancy (VO), zinc interstitial (Zni) and their complexes.
A B S T R A C T The luminescent semiconductor QDs are important materials because of applications in lasers, sensors, light-emitting diodes, biomedical labeling, biomedical imaging and solar cells. We have systematically studied the influence of five different capping agents on the structural and optical characteristics of CdZnS quantum dots (QDs) synthesized by the simplest aqueous method. The modified QDs were characterized by the UV–visible spectroscopy, X-ray diffraction, steady-state photoluminescence (PL), time-resolved PL, and transmission electron microscopy. We found that band-gap and PL characteristics of CdZnS QDs can be varied by using different capping agents. The CdZnS QDs capped with ethylene diamine (EDA) and mercaptoacetic acid (MAA) showed high PL intensities when compared to other capping agents. The UV–Vis absorption spectra were used to calculate the optical band-gaps: 2.63 eV (MAA), 2.56 eV (MPA), 2.42 eV (CA), 2.64 eV (Glucose) and 2.62 eV (EDA) of five different QDs: The time-resolved PL spectroscopy indicated slowest bi-exponential fluorescence decay rate for the MAA-capped CdZnS (CdZnS-MAA) QDs.
2014
Cadmium Zinc sulfide (Cd1-xZnxS) nanocrystals have been synthesized for different values of x (x= 0.0, 0.25 and 0.50) by chemical synthesis route. The structural studies were carried out by using X-ray diffraction (XRD) studies. Diffraction pattern reveal that samples are crystalline in nature having hexagonal (wurtizite) structure. Absorption spectra of specimens have shown blue shift in absorption edge in compared to bulk. Electroluminescence (EL) studies have revealed that EL starts at lower threshold voltage on increasing the Zn content in the ternary compound.
The mechanism of the photoluminescence changes in bio-conjugated CdSe/ZnS quantum dots
Applied Surface Science, 2013
The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed.
Optical spectroscopy of single Cd0.6Zn0.4Te/ZnTe quantum dots on Si substrate
Thin Solid Films, 2011
a b s t r a c t Keywords: Cadmium zinc telluride II-VI compound semiconductors Quantum dots Si substrate Single dot spectroscopy Photoluminescence Molecular beam epitaxy Microphotoluminescence (μ-PL) measurements were carried out to investigate the optical properties of single Cd 0.6 Zn 0.4 Te/ZnTe quantum dots (QDs) grown on Si substrate by using molecular beam epitaxy. The high quality of single Cd 0.6 Zn 0.4 Te/ZnTe QDs is witnessed by resolution-limited emission, negligible background and absence of measurable spectral jitter or blinking. Polarization-dependent and powerdependent μ-PL spectroscopy measurements were performed to identify the exciton, the biexciton, and the charged exciton in the emission spectra of single QDs. Furthermore a weak linearly polarized line is observed on the low energy side of the neutral exciton and is ascribed to dark exciton recombination.
RSC Advances, 2020
Tunable copper doped Zn 1Àx Cd x S alloy quantum dots (QDs) were successfully synthesized by the wet chemical method. A one-step method is developed to synthesize doped ternary QDs which is more preferable than a two-step method. The influence of experimental parameters like the Zn/Cd ratio and Cu dopant concentration has been investigated using various spectroscopic techniques like UV-visible, photoluminescence, X-ray diffraction and Raman spectroscopy. The absorption and emission properties can be tuned by changing the concentration of components of the ternary QDs. The high concentration of dopant completely quenched the emission of the ternary QDs. EDX gives confirmation of the elemental composition of the synthesized samples. The obtained results suggest the successful doping of the ternary QDs. Interestingly, the study results revealed that the crystal structure (ZB and/or WZ) and the dual emission of the Cu-doped Zn 1Àx Cd x Se alloy QDs could be controlled by varying the dopant concentration and chemical composition of the host. Doping also leads to enhancement in emission properties and provides more stability to ternary QDs. The enhancement in the photoluminescence (PL) decay lifetime of Cu-doped ternary QDs can be advantageous for optoelectronic and biosensor applications.