S P Lochab
Articles written in Bulletin of Materials Science
Volume 33 Issue 5 October 2010 pp 535-541
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:
wet chemical co-precipitation in non-aqueous medium (i.e. methanol);
wet chemical co-precipitation in aqueous medium (deionized water) and
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.
Volume 34 Issue 4 July 2011 pp 673-676
The nanocrystalline CaS : Ce nanophosphors are synthesized by wet chemical co-precipitation method. The particles possess an average size of 10 nm as calculated using Debye–Scherrer formula. The particle size and the crystalline nature of the formed nanoparticles are confirmed by TEM micrograph. The optical studies are carried out using UV–Vis absorption spectroscopy. The absorption edge is found to show blue shift with increasing cerium concentration. The shift may be attributed to Burstein Moss effect.
Volume 34 Issue 4 July 2011 pp 683-687
Bismuth doped barium sulphide nanocrystallities were prepared and characterized by XRD. Thermoluminescence (TL) studies of these samples after exposure to gamma radiation were carried out. The TL glow curve of the phosphors have two peaks at 403 K and 658 K while in their bulk counterparts these peaks were reported at 486 K and 570 K (Rao 1986). We noted that TL intensity increases with gamma exposure time in the range 30 min – 41 h which may be explained on the basis of track interaction model (TIM) and a high surface to volume ratio for the nanostructures. The kinetic parameters at various heating rates namely activation energy (E), order of kinetics (b) and frequency factor (s) of BaS : Bi (0.4 mol%) sample was determined using Chen’s method. The deconvolution of curve was done using the GCD function suggested by Kitis. The effect of different heating rates and different amount of dose has also been discussed.
Volume 42 | Issue 5