Red luminescent manganese-doped zinc sulphide nanocrystals and their antibacterial study.

Water soluble, uniform-sized ZnS:Mn2+ nanocrystals (NCs) have been prepared using a simple co-precipitation method with a methanol and water binary mixture as a reaction medium. The structure of the prepared ZnS:Mn2+ NCs is cubic with a mean size distribution of 3-5 nm. Photoluminescence (PL) studies showed emission at ∼612 nm, which is 22 nm red shifted as compared with the reported literature. This red shift could be attributed to the observed distortion in the imaged lattice plane. The capping effect of pepsin, citric acid and biotin on the optical properties of ZnS:Mn2+ NCs has been examined and the maximum enhancement in PL Intensity was found in the case of biotin. The synthesised ZnS:Mn2+ NCs were characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) for investigation of their structural properties. Because of the high PL intensity, biotin capped ZnS:Mn2+ NCs were further investigated for their anti-bacterial activity against gram negative and gram positive bacteria. These NCs show broad spectrum antibacterial activity against both types of bacteria having an MIC value of 100 ng ml-1 for B. subtilis.

Size dependence of Eu-O charge transfer process on luminescence characteristics of YBO3:Eu3+ nanocrystals.

Well-crystallized pure hexagonal phase YBO(3):Eu(3+) nanoparticles are prepared by the reverse micelles method. Vacuum ultraviolet photoluminescence (VUVPL) spectroscopy showed size-dependent nonlinear luminescence enhancement with remarkably improved chromaticity (0.62, 0.34), as compared to the commercial bulk YBO(3):Eu(3+) phosphor (0.56, 0.39). The quenching concentration of Eu(3+) doping and the ratio of red ((5)D(0)-->(7)F(2)) to orange ((5)D(0)-->(7)F(1)) emission was found significantly enhanced with the decrease in particle size, making it an ideal VUV phosphor for plasma display panels. The possible explanation for size dependence of the Eu-O charge transfer process via lowering of the structural symmetry is proposed in detail.

Differential susceptibility of Escherichia coli cells toward transition metal-doped and matrix-embedded ZnO nanoparticles.

Dependence of the antibacterial behavior on ZnO (TM-doped and surface-modified) nanoparticles on Escherichia coli cells has been investigated. ZnO nanoparticles that differ in size, activator ion and in the microenvironment in which these nanoparticles are embedded were used. Comprehensive antibacterial studies of these ZnO nanoparticles owing to their size and surface defects are carried out against E. coli cells. These studies have been carried out both in Luria-Bertani medium and on solid agar medium in the presence and absence of light. The differences in antibacterial effect have been quantified in terms of minimum inhibitory concentration, minimum bactericidal concentration, colony forming unit counts, and qualitatively evaluated by growth curves and disk diffusion tests. The difference in antibacterial activities of the ZnO nanoparticles may be attributed to the enhanced or reduced oxygen vacancies and defect states and could be attributed to the increased or decreased surface defects.

Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles.

Single-phase ZnO:Co(2+) nanoparticles of mean size 2-8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co(2+) ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co(2+), the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co-Co ions suppressed the ferromagnetism at higher doping concentrations of Co(2+). Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies.