G. Murali

Structural and optical studies on Mg doped CdS nanoparticles by simple co-precipitation method

Pure and Mg doped CdS (5at. %) nano particles were prepared for the first time by co-precipitation method using cadmium acetate, magnesium acetate and sodium sulfide as precursors. Compositional, structural, and optical studies were carried out by XRD, EDS, DRS and PL methods. Band gap widening was observed in the samples compared to bulk CdS (2.42 eV). Red shift of peak was observed in PL studies by doping Mg2+ in to the CdS.

Structural and Optical Characteristics of Ni Doped ZnS Nanoparticles

Nanocrystalline ZnS and Ni doped ZnS powders were synthesized by a simple chemical co-precipitation method at room temperature using sodium sulfide and acetates of Zinc and Nickel. 2-Mercapto ethanol is used as a capping agent. Structural and optical properties of as prepared samples were characterized using X-Ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Analysis using X-rays (EDAX) and Photoluminescence studies (PL). EDAX measurements confirmed the presence of Zn, Ni and S in the prepared samples. XRD analysis reveals that the Zn1-xNixS (x= 0.00 and 0.01) nanoparticles crystallized in zincblende structure. The average particle sizes of the nanoparticles are in the range of 2-3 nm. Shifting of photo luminescence peak to higher wavelength along with intensity quenching is observed for doped ZnS nanocrystals (NCs).

Room Temperature Ferromagnetism in Cr‐doped ZnS Nanoparticles

Cr‐doped ZnS nanoparticles with Cr concentration of 2 atm.% were successfully synthesized by the chemical co‐precipitation method using 2‐mercapto ethanol as the capping agent. The structural, optical characteristics and magnetic properties of the prepared samples were studied. Energy Dispersive spectroscopy (EDS) measurements showed the existence of Cr ion in the Cr doped ZnS. No mixed phase was observed from X‐ray diffraction (XRD) studies and all the peaks were indexed to the cubic phase of ZnS. The diameter is in the range of 5–10 nm, it was confirmed by TEM studies. The photoluminescence spectra of all the samples exhibited a broad emission band located around 435 nm. The luminescence intensity decreased by doping Cr. The magnetic behavior of the nanoparticles for Cr doped ZnS was investigated using a vibrating sample magnetometer (VSM). We determined the magnetic parameters such as saturation magnetization (MS), coercivity (HC) and retentivity (MR) with Cr concentration from M‐H loop.

Structural and optical response of mixed phase CdS nanocrystals to Ni2+ ions

Cadmium sulfide (CdS) semiconductor nanocrystals doped with Ni2+ have been synthesized via a solution-based method and employing 2-mercaptoehonal as a capping agent. The obtained nanocrystals were characterized using X-ray diffraction (XRD) and Diffuse reflectance spectroscopy studies (DRS). XRD results showed that the undoped CdS nanocrystals are in mixed phase of cubic and hexagonal, where as the doped CdS nanocrystals in hexagonal phase. DRS results supported the mixed phase of undoped nanocrystals by showing two absorption edges at 363 nm and 428 nm. The absorption edge at 363 nm can be attributed to cubic phase while the other can be attributed to hexagonal phase of the sample. But for Ni2+ doped CdS nanocrystals only one absorption edge at 468 nm was observed. The observed red shift in the band edge of the nickel doped CdS nanocrystals is due to sp-d exchange interactions between the band electrons and the localized d-electrons of the Ni2+ ions substituting Cd2+ ions in the doped sample.

Influence of cobalt doping on the structural and optical properties of ZnS nanoparticles

ZnS: Co (0 and 2 at.%) nanoparticles have been successfully synthesized through a simple chemical method namely refluxing technique using PVP as a stabilizer. The prepared samples have been characterized using X-ray diffraction (XRD), Diffusion reflectance spectra (DRS) and Photoluminescence studies (PL). XRD patterns of the nanoparticles showed cubic phase with particle size of the order of 5–6 nm. Room-temperature photoluminescence (PL) spectra of the undoped samples exhibited emission in the blue region and doped samples also exhibited the same blue emission with enhanced intensity. DRS spectra of the samples showed an increase in the band gap on doping which further attested the incorporation of Co2+ into ZnS nanoparticles.

Synthesis and Optical Properties of Annealed Cr Doped ZnS Nanoparticles

Undoped and Cr doped ZnS nanoparticles with Cr concentrations of 3.0 at.% were prepared by a chemical co-precipitation method for the fist time, using 2-Mercaptoethanol as the capping agent and annealed the synthesized particles at 600°C for 3h in air. The effect of annealing on morphological, structural and optical properties of ZnS and ZnS:Cr have been studied and compared with as prepared samples. EDAX measurements confirmed the presence of Cr in the ZnS lattice and it also confirms the conversion of ZnS into ZnO after annealed at 600 0C/3h. Surface morphologies of all samples were characterized using scanning electron microscopy (SEM). XRD spectra of as synthesized nanoparticles of ZnS and ZnS:Cr exhibited cubic phase. After annealing, the cubic phase is transformed into hexagonal phase. The particle sizes of the ZnS:Cr powders were increased from 5 to 30 nm when the powders were annealed at 600°C. A stable blue emission peak at 445 nm is observed from the as prepared samples (pure ZnS and Cr doped ZnS) but annealed at 600 0C the PL peaked at 500 nm for pure ZnS and Cr doped ZnS nanoparticles exhibited PL peak at 500 nm as well as 654 nm. The emission intensity decreased in annealed particles compared to as synthesized samples.

Effect of Fe doping on structural and optical properties of CdS nanoparticles

Undoped and Fe doped CdS quantum dots have been prepared using simple precursors by chemical precipitation technique. X-ray diffraction (XRD) analysis reveals that undoped CdS nanocrystals are in mixed phase of cubic and hexagonal, where as the doped CdS nanocrystals are in hexagonal phase. Photoluminescence spectr (PL) spectra of doped nanoparticles showed a red shift when compared to the undoped nanoparticles.

Dopant Induced Room Temperature Ferromagnetism in Fe-Doped CdS Nanoparticles

Room temperature ferro-magnetism in Fe-doped CdS nanoparticles (NPs) synthesized by a wet chemical precipitation method is reported. Magnetic studies revealed that pure CdS NPs exhibit diamagnetic behavior as like bulk material, where as 3% Fe doped CdS NPs shows the ferromagnetic behavior. At room temperature, ESR signal characteristic of Fe3+ was observed in doped NPs.

2‐Mercapto Ethanol Passivated Zn1−xCrxS Nanoparticles

The Cr doped ZnS nanoparticles were successfully synthesized by chemical co precipitation method using mercapto ethanol as the template. As prepared nanoparticles were characterized by X‐Ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron Microscopy (TEM) and Optical absorption studies. We studied the effect of Cr doping on structural and optical properties of nanoparticles. XRD studies elucidated that the Cr ions were not affected the original cubic structure of ZnS, but lattice parameter decreased with Cr doping. The optical spectra showed a blue shift in the absorbance spectrum with increasing dopant concentration. We observed quantum mechanical effects such as an increase in bandgap (Blue shift) and lattice contraction with chromium doping.

Structural, optical and luminescence studies of ZnSe nanowires

Abstract ZnSe nanowires have been successfully synthesized through chemical vapor deposition assisted by laser ablation in a tube furnace on a silicon substrate coated with a gold film of 2 nm thickness. X-ray powder diffraction measurements reveal that the synthesized products had pure hexagonal wurtzite structure. The microstructures and chemical composition of the as-grown nanowires have been investigated by means of electron microscopy, energy dispersive spectroscopy, photoluminescence and Raman spectroscopy. The results reveal that the as-grown material consists of ZnSe nanowires with diameters ranging from 60 – 100 nm and with lengths up to several tens of micrometers. High resolution transmission electron microscopy and selected area electron diffraction indicated that as-synthesized nanowires were single crystalline in nature. Micro-photoluminescence studies on ZnSe nanowire reveal strong emission at 460 nm. The Raman peak at 251 cm−1 is attributed to the longitudinal optic phonon mode of ZnSe.