Effect of growth temperature on the structural, optical and luminescence properties of cadmium telluride nanoparticles

Cadmium telluride (CdTe) has been successfully prepared by a simple wet chemical process at different reaction temperatures. Temperature is one parameter that thermodynamically plays an important role in controlling the growth rate, morphology, size and size distribution of the as-prepared nanoparticles (NPs). Effect of this parameter was investigated on the growth, structural and optical properties of CdTe NPs. It was observed that the Powder X-ray diffraction (XRD) pattern for samples prepared at 50 °C had many impurities from unreacted precursors while those prepared at > 100 °C displayed polycrystalline NPs. The XRD results revealed that the structure of the CdTe NPs was cubic with the planes (111), (220), (311) being the main observed peaks. The crystallite sizes obtained from Scherrer formula increased with the increase in growth temperature (2.86–3.62 nm grown at 50–200 °C respectively). The scanning electron microscopy micrographs showed that the morphology of the nanoparticles possessed spherical-shaped particles over the entire surface. This was further confirmed by high resolution transmission electron microscopy micrographs which also displayed increase in the particle size with an increase in the growth temperature. In the optic study, the photoluminescence (PL) spectra displayed a red shift (540–560 nm) in emission as growth temperature increased from 50 to 200 °C. The highest PL peak intensity was realized at a growth temperature of 150 °C. Absorption band maxima were observed to shift towards longer wavelength for higher growth temperatures. The optical band gap decreased with increase in the growth temperature from 2.67 to 2.08 eV for 50–200 °C respectively

Effects of selenium concentration in the precursor solution on the material properties of cadmium selenide flower-like nanoparticles

CdSe flower-like nanorods (NRs) were successfully synthesized by Sol–gel technique where a simple aqueous technique was applied. The effects of different selenium (Se) concentration in the precursor solution on the material properties were studied. The X-ray diffraction (XRD) analyses show that a cubic zinc blende crystal structure was formed. Variation in the crystallite sizes were observed for different amounts of Se used in the precursor. The sizes estimated from various techniques were in the range 3–5 nm. The XRD peak intensity reached an optimum when 8 mL of 0.5 M of reduced selenium was used. The surface topography obtained from the scanning electron microscope showed densely packed and uniformly distributed flower-like rod/blade-like shaped CdSe NRs. The Fourier transform infrared spectrophotometer gave the stretching vibrations of the CdSe NRs with some bands belonging to the capping agent and the solvent. Thermal analysis conducted portrayed the 8 mL sample to be more stable than other samples at various temperatures. The photoluminescence (PL) studies displayed a red shift in the emission peaks (550–575 nm) as the selenium concentration was increased from 4 to 12 mL. This was then followed by an increase in the PL peak intensity which reached a maximum at 8 mL of Se used during the synthesis. The band gap energies calculated from the absorption spectra decreased from 3.27 to 2.79 eV with an increase in the Se concentration. The percentage transmittance of CdSe NRs varied with different amounts of Se in the precursor solution

A comparison investigation of optical, structural and luminescence properties of CdOxTe1−x and CdTexSe1−x nanoparticles prepared by a simple one pot method

We present L-cysteine capped CdOXTe1−X and CdTeXSe1−X nanoparticles (NPs) prepared in one pot. The as-prepared CdOXTe1−X NPs were found to have a hexagonal crystal structure of CdTe with a cubic phase of CdO. There was, however, change in phase to cubic type when 2 mM of Se was introduced into the CdTe at 60 min of reaction time. The average crystallite sizes obtained from X-ray diffraction analysis for CdOXTe1−X and CdTeXSe1−X NPs were in the range of 10–36 nm. The diffraction peaks shifted to higher diffraction angle with longer growth time. Scanning electron microscope images display change in shape and size as reaction progress. Photoluminescence (PL) emission was observed to shift from 510–566 nm and 620–653 nm for CdOXTe1−X and CdTeXSe1−X NPs respectively followed by variation in the peak intensities. The emission spectra displayed a good symmetry and a narrow full width at half maximum ranging from 41 to 100 nm in both cases. The absorbance analysis of the as-prepared NPs displayed well-resolved absorption bands. The optical band gaps of the as-prepared NPs were found to decrease with increase in reaction time. Reaction parameters such as pH, reaction time, reaction temperature and the molar concentration could have major effects on the optical properties of the as-prepared nanoparticles hence their need to control them

Effects of precursor pH on structural and optical properties of CdTe quantum dots by wet chemical route

l -cysteine capped CdTe quantum dots (QDs) were synthesized in aqueous solution in open air. In order to improve the crystallinity of the CdTe QDs, synthesis conditions were optimized. Effects of different solution pH were investigated in order to determine the optimum pH for the growth of highly crystalline CdTe QDs. X-ray diffraction patterns (XRD) for all the as-prepared samples displayed a zinc blende crystal structure. The XRD peak intensities were found to increase to a certain pH level. This was accompanied by a general increase in the crystallite sizes (3.01–3.25 nm) of the CdTe QDs as the solution pH was gradually increased from 7 to 12.5. The calculated strain in the CdTe QDs was observed to decrease with an increase in the solution pH level. The morphological studies obtained from scanning electron microscope showed clear changes in the shape of CdTe QDs with various solution pH. The shape of the QDs changed from small spherical to large flower-like and needle-like structures for various solution pH. The optical spectroscopy studies revealed that the photoluminescence emissions were shifted to longer wavelength (545–593 nm) as the pH was increased from 7 to 12.5. The ultraviolet–visible analysis displayed a red shift in the absorption peaks with an increase in the pH levels. The optical band gaps obtained from the Tauc formula displayed an inverse relation with the solution pH which could be due to increase in the QDs’ sizes with increasing pH level

Structural and optical properties of novel CdSe nanoparticles produced via a facile synthetic route: Studies on the effects of cadmium sources

We report on the successful synthesis of CdSe nanoparticles (NPs) via a facile aqueous approach. Investigation on the effects of various cadmium sources in the precursor solution on the CdSe NPs is discussed. The structural and morphological properties characterized by the X‐ray diffraction (XRD) and scanning electron microscope (SEM) displayed good features of the as‐prepared CdSe NPs. The XRD pattern displayed a pure zinc blende crystal structure for all samples, with the most crystalline sample observed for CdSe NPs prepared using anhydrous cadmium chloride. The estimated crystallite sizes were below 6 nm for all the CdSe NPs samples. Mixed shapes of spherical and nanorods of varying sizes were observed from the SEM images for the as‐prepared NPs prepared using different cadmium sources. The optical studies conducted by photo‐spectroscopy pointed out the CdSe NPs prepared using anhydrous cadmium chloride gave the best optical properties. The emission wavelengths were in the range 565 to 574 nm while the optical band gaps were in the range 2.94 to 3.23 eV for all the as‐prepared CdSe NPs samples. All the samples, however, displayed quantum confinement effects giving room for further fabrication and engineering to suit specific applications in the biological field. The obtained results demonstrated that aqueous phase synthetic route employed in this study could be successfully adopted for production of high‐quality CdSe NPs because of its facile and inexpensive nature

Structural, optical and luminescence properties of CdTe quantum dots: Investigation on the effect of capping ligand ratio

Well-crystallized cadmium telluride quantum dots (CdTe QDs) were fabricated by a simple wet chemical process under open air condition at a growth temperature of 100 °C. Various amounts of the capping ligands were used in order to study the effects of them on the structural, optical and luminescence properties of C dTe QDs. The structural properties were studied using x-ray diffractometer (XRD) and scanning electron microscope (SEM). All the as-obtained CdTe QDs displayed a zinc blende crystal structure with no extra phases observed in the XRD analysis. The diffraction reflection intensities were enhanced with an increase in the capping ratio with the optimum condition achieved at a capping ratio of 1.2. The average particle sizes estimated from various techniques increased with an increase in the amounts of capping ligands used (2.14, 3.19, 2.75, 3.00, 3.27 and 4.47 nm for 0.8, 1.0, 1.4, 1.6 and 2.0 capping ratio). The SEM analysis revealed spherical shaped CdTe QDs with string-like features covering the surface of the QDs observed at higher capping ratio. Aggregation of the CdTe QDs was observed for the QDs prepared at a lower capping ratio (Cd:Cyst of 1:0.8). The Photoluminescence (PL) studies displayed a red shift in the emission wavelength accompanied by variation in the emission peak intensity. The emission wavelength shifted from 558–571 nm for 0.8–2.0 capping ratio. Highest PL emission peak intensity was obtained at a capping ratio of 1.2 which was in line with the results obtained from the XRD. The absorbance of the as-prepared CdTe QDs increased while the band gap decreased with increasing capping ratio due to the growth of the QDs

Capping Ligand Influence on the Structural, Optical and Luminescence Properties of CdTe Nanoparticles Prepared by a Simple Wet Chemical Process

The nature of the capping ligands used and the strength of their interactions with the surface atoms of the nanoparticles (NPs) impact greatly on the material properties and the stability of the resulting NPs. The structural analysis revealed that all the as‐prepared CdTe NPs samples had a zinc blende crystal structure of different phases. The glutathione and L‐cysteine capped CdTe NPs had the same zinc blende phase (JCPDS no. 75–2086) while thioglycolic acid capped and co‐capped CdTe NPs possessed another zinc blende phase (JCPDS no. 75–2083). The calculated crystallite sizes were in the range 2–26 nm for all the samples. The optical spectroscopy studies showed various properties when different capping ligands were used. The band gap energies for all the as‐prepared CdTe NPs confirmed the results obtained from the X‐ray diffraction. The band gap energies were in the range of 2.39–3.34 eV for all the as‐prepared CdTe NPs

The influence of reaction times on structural, optical and luminescence properties of cadmium telluride nanoparticles prepared by wet-chemical process

This paper explains one pot synthesis of type II water soluble L-cysteine capped cadmium telluride (CdTe) core shell quantum dots using cadmium acetate, potassium tellurite and L-cysteine as the starting materials. The reaction was carried out in a single three necked flask without nitrogen under reflux at 100 °C. Results from PL show a sharp absorption excitonic band edge of the CdTe core with respect to the core shell which loses its shoulder during the growth of the shell on the core. The PL spectra indicate a drastic shift in emission window of the core which is simultaneously accompanied by an increase in emission intensity. X-ray diffraction pattern confirms the formation of hexagonal phase for all samples. Some difference in absorption edges were observed due to varying synthesis time of CdTe NPs. The position of the absorption band is observed to shift towards the lower wavelength side for shorter durations of synthesis