Synthesis and blue emission properties of Co-doped CdS semiconductor nanoparticles

Background: Cadmium sulfide (CdS) based semiconductors are of great interest for different high-end applications because it poses direct bandgap (2.42 eV). CdS are the primary constituent material in many applications, namely solar cells, electroluminescent, and quantum dot light-emitting diodes. Transition metal-doped CdS revealed considerable influence in the bandgap, photoluminescence properties, and peak energy upon increasing the metal content. Objective: In this work, we study the single-phase cubic structure of CdS. Photoluminescence spectra revealed a strong blue emission peak located at about 445 nm. Methods: We investigate the Co-doping CdS semiconductor nanoparticles prepared via the chemical co-precipitation method using thiophenol as a template, 300 °C/2h in vacuum optimum temperature, and annealing period to yield nanosized particles. Morphology and structural studies of the particles were using XRD and TEM, respectively. Results: XRD and TEM studies for the calcined samples revealed a cubic structure. The crystalline size was in the range of 10-17 nm. Thermo gravimetric analysis (TGA) was employed to stabilize the temperature of annealing for the samples. Photoluminescence spectra revealed a strong blue emission peak around 445 nm, indicating surface states within the band gap region, a characteristic feature of nanoparticles. The blue shift in the spectra and the band gap value of Co-doped CdS nanoparticles was estimated using UV-vis absorption spectra. Conclusion: XRD analysis indicated zinc blende structure, and the intensity decreased with increasing Co content. TEM images show that the particles are spherical with average sizes around 13 nm. Luminescence of the synthesized nanoparticles exhibited blue emission between 400 – 500 nm, with the peak located at about 445 nm. The emission intensity increased with the increase in Co concentration.

Carbon Quantum Dots as Fluorescence Turn-Off-On Probe for Detecting Fe3+ and Ascorbic Acid

This work describes a “turn-off-on” fluorescence probe based on carbon quantum dots for sensing Fe3+ and ascorbic acid. The carbon quantum dots are prepared by hydrothermal method using a biocarbon source of black sesame. When excited at 355 nm, the carbon quantum dots show a strong bright blue emission peak centered at 438 nm. Obviously, the decrease of the fluorescence intensity of carbon quantum dots can be seen upon addition of Fe3+. Interestingly, the fluorescence quenching can be regained after the addition of ascorbic acid. The mechanism is that the added Fe3+ was destroyed by reductive ascorbic acid because of the redox reaction between ascorbic acid and Fe3+, making the fluorescence of the system recovered. The obtained curves are linear for Fe3+ and ascorbic acid over the range 50–1500 μM and 32.2–987.6 μM, respectively. The detection limits for Fe3+ and ascorbic acid are 2.78 μM and 0.0344 μM, respectively. Thus the carbon quantum dots can be used as a dual-function fluorescent sensor to achieve sensitive detection of Fe3+ and ascorbic acid.

Highly Efficient Yttrium Based Metal Organic Framework for Removal of Pollutant Dyes

Highly porous crystalline luminescent metal Organic Frameworks (MOFs) were synthesized by conjugating Yttrium nitrate and Benzene Tri Carboxylate (BTC) in the presence of surfactant Cetyl Tri methyl Ammonium Bromide. A characteristic blue emission peak around 400 nm of Y upon excitation with UV light and peaks through Infra-Red spectroscopy revealed the formation of co-ordinate bond between Y and BTC, thereby confirming the formation of MOF nanoparticles (NPs). The nanoparticles were studied for potential removal of pollutants by encapsulation of the dye methylene blue (MB). Optical analysis affirmed the encapsulation of dye particles within the porous MOF NPs as dye absorption decreased around 600nm. This study offers great promise of using MOF NPs as platform for sensing of analytes in solution and removal of pollutant materials.

Photoluminescence Property Study on Patterned Growth of Aligned ZnO Nanowire Arrays

The patterned ZnO rods were fabricated by the photoresist pattern covered sputtered ZnO film assisted hydrothermal deposition.The ordered ZnO nanorods were prepared by the reaction in sodium citrate and Zinc nitrate solution. The sodium citrate and photoresist hole works together for crystallization vertically to the c axis of ZnO. A UV emission at 395nm and an intense green-blue emission peak at 580nm were observed from the ordered ZnO nanorods which reflect the crystallization of ZnO rods. The influence of different growth reaction times and micro-sized holes on the photoluminescence property and crystal quality of ZnO nanowires arrays were investigated.

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.

Microwave Hydrothermal Synthesis of GaN Nanorods

The GaOOH Nanocrystal rods were successfully synthesized by microwavehydrothermal method using Ga2O3 ,HNO3 and NH3·H2O as raw materials. Simple heat treatment of GaOOH in the flow of NH3 gas leads to the formation of submicron GaN rods even at 800°C through GaOOH. The resultant GaOOH and GaN nanomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism of GaOOH and GaN was proposed. The results indicate that the as synthesized GaN were hexagonal nanorods with average aspects ratio of 5:1(diameter 800 nm and length about 4μm). Photoluminescence spectrum shows that a blue emission peak originates at 473.5 nm, indicating that the GaN nanorods displayed luminescence emission in the blue-violet region, which was related to crystal defects, and may be helpful for electro-optical applications of GaN material.