Optical Properties Of CdS Nanoparticles Research Articles

Effect of Cr-doping on the structural and optical properties of CdS nanoparticles prepared by chemical precipitation method

Undoped and Cr doped CdS nanoparticles have been prepared by chemical precipitation method. X-ray diffraction analysis reveals that the undoped and Cr doped CdS nanoparticles exhibit hexagonal structure and the average particle size of the nanoparticles is in the range of 2.2–3.8 nm. The HRTEM studies show that the average particle size of undoped and Cr doped CdS nanoparticles is in the range of 2–3.7 nm. The compositional analysis results indicates that Cd, S and Cr are present in the samples. From the optical studies it is observed that the absorption edge of the prepared CdS and Cr doped CdS nanoparticles are shifted towards the shorter wavelength region (blue shift) when compared to that of bulk CdS and this shift is due to the quantum confinement effect present in the samples.

Synthesis and characterization of CdS nanoparticles in the presence of oleic acid as solvent and stabilizer

Oleic acid (OA)-capped CdS nanoparticles (NPs) have been successfully synthesized via the direct reaction of Cd(CH 2COO) 2·2H 2O with S powder in OA solvent at 230 °C under nitrogen flow, which was a kind of clean and air-stable solvent. The morphologies and structures of the as-synthesized CdS NPs are examined by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectroscopy, and the typical Ostwald ripening growth mechanism is concluded. Moreover, the collected ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy demonstrate good optical properties of CdS NPs.

Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles

We have investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in bandgap with size-quantization was investigated by UV-VIS absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH)2 nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H2S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.

Poly(styrene- b-2-(N,N-dimethylamino)ethyl methacrylate) diblock copolymers: Micellization and application in the synthesis of photoluminescent CdS nanoparticles

Fluorescence studies on amphiphilic diblock copolymers of styrene and 2-(N,N-dimethylamino)ethyl methacrylate using 1,8-anilinonaphthalenesulfonate (ANS) as fluorescent probe revealed the formation of stable micelles at extremely low polymer concentrations of ∼0.05%. The micellar microenvironment was characterized by an average polarity of E T(30) = 44–48 kcal mol −1, similar to the moderately polar solvents, and extremely high microviscosity. Increase in hydrophilic: hydrophobic ratio of the copolymers resulted in an increase in the average polarity and decrease in microviscosity. The micelles proved to be excellent hosts for the synthesis and stabilization of photoluminescent CdS nanoparticles with a high degree of quantum confinement and broad photoluminescence, dominated by trap-state emission. Moreover, the size and size-related steady-state optical properties of CdS nanoparticles were significantly dependent on the microenvironment of the host micelle. In contrast, the photoluminescence dynamics of the nanoparticles, involving time-scales from 100 ps to 100 ns, are similar in all cases. Interestingly, the nanoparticles exhibit a large time-dependent Stokes shift, 75% of which is complete within the first ∼100 ps after the excitation. The extremely rapid Stokes shift is attributed to the decay of the initially formed band-edge excitons in a time-scale too fast to be affected by the microenvironment surrounding the particle.

Preparation and optical properties of CdS nanoparticles dispersed in poly(2-(dimethylamino)ethyl methacrylate-co-acrylic acid) co-polymers

CdS/poly(2-(dimethylamino)ethyl methacrylate-co-acrylic acid) nanocomposites were prepared and characterized using structural, optical and thermal methods. Co-polymers used as the matrices were synthesized by radical polymerization of the co-monomers in different mol ratios (1:1, 2:1 and 1:2, DMAEMA:acrylic acid). The presence of the nanostructured CdS was confirmed by TEM analysis as well as by the shift of the onset of the optical absorption towards lower wavelengths. XRD spectra showed the cubic crystal phase of the obtained CdS nanoparticles. TGA measurements revealed improved thermal stability of the nanocomposite with respect to pure co-polymer matrix.

Study of photophysical properties of capped CdS nanocrystals

Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO 2) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO 2-capped nanoparticles. It is found that the average decay time 〈 τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO 2 and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO 2, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency.

Optical properties of CdS nanoparticles and the energy transfer from CdS nanoparticles to Rhodamine 6G

In the present work, we report the synthesis of colloidal CdS nanoparticles with different sizes and the band gaps of these samples exhibit a systematic dependence on the size of particles. We also study the photophysical properties of CdS nanoparticles and the energy transfer from CdS nanoparticles to Rhodamine 6G dyes by steady state and time resolved photoluminescence spectroscopy. The experimental results show that the relaxation of the excited state of CdS nanoparticles is composed of three different components. The calculated energy transfer efficiency from CdS nanoparticles to dye is 43% for 3.0 nm CdS nanoparticles.

Synthesis, characterization and optical properties of CdS nanoparticles confined in SBA-15

A novel and dexterous in situ method is introduced to load CdS nanocrystals into SBA-15, which uses the acid–base reaction of mercaptoacetic acid with 3-aminopropyltriethoxysilane, the modifier of internal surface of mesoporous materials to facilitate loading of sulfur precursor, followed by adsorption of Cd 2+ and calcination at 300 °C in N 2 atmosphere for 2 h. XRD, N 2 adsorption–desorption isotherms, HRTEM, EDS, FT-IR, UV–vis absorption spectrum and PL spectrum were used to characterize the composite material. It was found that the CdS nanocrystals were confined in the channel of SBA-15 with an average size of 6 nm. The mesoporous silica-supported CdS composites showed a room temperature photoluminescence property.

Size control and photoluminescence enhancement of CdS nanoparticles prepared via reverse micelle method

Uniform CdS nanoparticles from 4 to 8 nm have been synthesized via a quaternary reverse micelle method. The size of the nanoparticles can be controlled and modulated by adjusting the W ( W=[H 2O]/[CTAB]) value. In order to eliminate the surface defects and improve the optical properties of CdS nanoparticles, the reflux treatment was employed. Compared with the freshly prepared CdS nanoparticles which mainly presented the broad defect emission, the nanoparticles treated by reflux exhibited narrow band size dependent exciton emission and its intensity was enhanced greatly, due to the effective surface modification. The possible mechanism of effective surface modification is discussed and the highest quantum yield of CdS nanoparticles at room temperature is estimated to be 11%.

Synthesis and optical properties of nanosized CdS prepared in a quaternary CTAB/ nhexanol/n-heptane/water reverse micelle

Quaternary water-in-oil reverse micelles consisting of cetyltrimethylammonium bromide (CTAB), nhexanol, n-heptane and water were prepared and characterized. The optimized reaction conditions were determined, and monodispersed droplets of the reverse micelles were used as microreactors to synthesize CdS nanoparticles. By using transmission electron microscopy (TEM), UV-Vis spectroscopy and fluorescence spectroscopy, the influences of the reverse micelle components on the size, size distribution, morphology, stability and optical properties of CdS nanoparticles were investigated. CdS nanoparticles with narrow size distribution were obtained and the size range is 6–8 nm whenW=24 (W=[water]/[CTAB]), P=5.27 (P=[n-hexanol]/ [CTAB]), [CTAB]=0.2 mol/L, [Cd2+] and [S2-] are 8.45×10−4 mol/L.

Effect of different capping environments on the optical properties of CdS nanoparticles in reverse micelles

CdS (E=2.5 eV) nanoparticles were synthesized in reversed micelles and capped with materials of different band gaps and charge compensation ability: Cd(OH)2 (4.0 eV), ZnS (3.2 eV), and CdO (2.3 eV). The preparations allowed the examination and comparison of the efficiencies of confinement of the electron and hole by the various capping materials. The absorption and emission spectra of the capped CdS nanoparticles suggest the following: (1) Efficient capping and strong quantum confinement are observed for CdS particles of small size (<3.8 nm), showing well-resolved photoexcitation spectra; (2) the confinement efficiency improves with capping thickness; (3) although ZnS has smaller band gap than Cd(OH)2, it was more efficient in surface-charge compensation and it is the best capping agent of the three materials; and (4) the similar band gaps of CdO and CdS resulted spectroscopically in strong mixing between the excited states of these materials. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 439–450, 1999