Optical Properties Of CdSe Quantum Dots Research Articles

Influence of crystalline mediums KCl and KDP on structural and optical properties of embedded CdSe quantum dots

In order to pass comfortably to the practicalities of nanomaterials it is necessary to use, in general, a support like: films, amorphous hosts or crystalline hosts. So it is important to know the effect of hosts on structural and optical properties of nanomaterials, in this context, this investigation suggests to survey the behavior of CdSe quantum dots (QDs) dispersed in two different crystalline hosts the potassium chlorade KCl and the potassium Di-hydrogen phosphate KH2PO4 (KDP) single crystals, where they are prepared using tow different technics: the Czochralski (Cz) method and the lowering temperature from aqueous solution technic, respectively. The obtained results from X-ray diffraction (XRD) demonstrate that CdSe QDs have different preferred orientations inside these two hosts. This behavior will be discussed in detail. Nevertheless, the UV–vis and Phtoluminiscance (PL) spectroscopy prove that the optical properties of CdSe QDs have great similarity in these two hosts.

Encapsulation of highly confined CdSe quantum dots for defect free luminescence and improved stability

This is the first report on the generation of trap states and their effective elimination in highly confined CdSe quantum dots in order to obtain enhanced and stable optical properties prepared by aqueous route. Surface plays an important role in optical properties of quantum dots (QDs) and surface modification of quantum dots can improve optical properties. In present work luminescent CdSe QDs were prepared using 2-Mercaptoethanol (2-ME) as stabilizing agent and encapsulated by polymer. Different concentrations of 2-ME were used to tune the emission spectra with respect to their reduced size. Addition of 2-ME to CdSe QDs enhances the trap emission and quenching band edge emission due to (i) increased surface to volume ratio and; (ii) presence of high concentration of sulfide ions as confirmed from EDX analysis as sulfide ions possesses the hole scavenging characteristics. Polymer encapsulation of QDs was carried out to make them stable and to improve their optical properties. Even though there are previous reports addressing the improved optical properties by polymer encapsulation and silica encapsulation but experimentally it has not been reported yet experimentally. In this work we have synthesized and characterized water soluble polymer encapsulated QDs and proved the facts experimentally. Photoluminescence spectroscopy clearly reveals the role of polymer encapsulation in boosting the optical properties of CdSe QDs. FTIR spectra validate the presence of biocompatible functional groups on CdSe4/PEG (Polymer encapsulated QDs).

Facile synthesis of CdSe quantum dots in a high-boiling two-phase liquid/liquid system

We introduce a facile way to synthesize high-quality CdSe quantum dots (QDs) in a high-boiling two-phase liquid/liquid system. The cadmium myristic acid salt (Cd-MA) dispersed in the dimethylbenzene and selenourea dissolved in the ethylene glycol (EG) reacted at the two-phase interface for the nucleation and growth of nanocrystals. The n-trioctylphosphine oxide (TOPO) was used as capping agent of the CdSe QDs. In this route, the selenourea used as the precursor was dissolved in viscous ethylene glycol (EG), which facilitated the control of the nanocrystal growth by virtue of the slow decomposition and diffusion of selenourea in EG. The size, shape, crystalline structure and optical properties of CdSe QDs were investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV⿿vis spectrometer and photoluminescence spectroscopy. This route could be exploited to synthesize nanocrystals with a large scale and could broaden to synthesis of metal or other semiconductor nanocrystals.

Composition-controlled optical properties of colloidal CdSe quantum dots

A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

The Optical Properties of CdSe Quantum Dots by Using Spray-Atomization Method

Cadmium Selenide (CdSe) quantum dots (QDs) is inorganic material by using spray-atomization method which is the novelty to find out the optical properties for the CdSe QDs. The Selenium (Se) precursor and Cadmium (Cd) precursor were prepared first. Se precursor by using sodium sulfite aqueous was mixed with selenium (Se) powder. For Cd precursor was used cadmium chloride (CdCI) as the Cd precursor. From previous research, CdSe QDs was obtained by using capping agent such as tri-n-octylphosphine oxide (TOPO) and trioctylphosphine (TOP). These capping agent are hazardous to environment and human. By using spray-atomization method it is more safe and economically. The photoluminescence (PL) was used to investigate the optical properties and to investigate the energy band gap from PL result. The field emission scanning electron microscopy (FESEM) was used to know the surface morphology of CdSe QDs. By PL result, the energy band gap was calculate and the comparison was investigate between the size of particle and the energy band gap. This important in this paper is to investigate the optical properties of CdSe QDs by using sprays-atomization method and to relate with the particle size.

Biomimetic synthesis of CdSe quantum dots through emulsion liquid membrane system of gas‐liquid transport

AbstractThe cadmium selenide quantum dots (QD) have been synthesized by template‐control in an emulsion liquid membrane system. The system consisted of kerosene as solvent, L152 (dialkylene succinimide) as surfactant, N7301 (trialiphatic amine, Ra, R=C8‐C10) as carrier, 0.1 mol/L CdCl2 solution as internal‐aqueous phase and H2Se gas as external phase. Additive organic template agent in internal‐aqueous phase was necessary to fom CdSe QD. The influence of the nature of template and its concentration on sizes of the formed CdSe QD has also been studied. Transmission electron microscopy showed that the sizes of the products could be controlled down to 3‐4 nm. X‐ray diffraction analysis revealed that the crystals had cubic structure. The formation process and the optical properties of CdSe QD have also been presented.