Cobalt doped zinc oxide nanoparticles (NPs) and nanorods (NRs) were synthesized by a simple chemical method. An increase in the formation of nanorods with an increase in cobalt doping is found to occur from scanning electron microscopy and transmission electron microscopy studies. Powder X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction confirm the formation of a wurtzite crystal structure of ZnO. Shifting and broadening of the bands at 437 cm⁻¹ and 579 cm⁻¹ in the micro-Raman study of Co-doped ZnO nanostructures indicates the incorporation of Co in ZnO. Shifting of the absorption edge to lower wavelength and blue shift of the band gap is observed in UV-visible spectra of Co-doped ZnO samples. Field-dependent magnetization measurements exhibit diamagnetic behavior down to 2 K in the case of ZnO whereas Co-doped ZnO samples show coexistence of superparamagnetic and ferromagnetic behavior at room temperature and at 2 K. The observed ferromagnetism may have originated due to the exchange interaction between the localized d electrons in Co²⁺ atoms and free carriers generated due to Co-doping as well as due to cobalt clustering in the Co-doped samples.

The present study investigates the influence of cobalt doping on the structural and magnetic properties of TiO₂ nanoparticles prepared by a simple wet chemical method.

In the present investigation, synthesis, characterizations and the tuning of the optical band gap (E_g) of ZnO nanowires (NWs) has been successfully achieved by introducing Mg as an intentional impurity with varying concentrations Zn_1−xMg_xO (x = 0, 5, 10 and 20 at. %). Although the ionic radius of Mg²⁺ (0.57 Å) is close to that of Zn²⁺ (0.60 Å) the crystal structure difference and large lattice mismatch between ZnO (wurtzite, 3.25 Å) and MgO (rock salt, 4.22 Å) causes phase segregation in Zn_1−xMg_xO with Mg compositions between 37% < x < 62%. Optical measurements of the as grown and Mg doped ZnO NWs shows the optical bandgap tunability from ∼3.35 eV to 3.65 eV as a function of the Mg content. Rietveld refinement of XRD data for the Mg doped ZnO nanowires confirm the wurtzite structure and a continuous compaction of the lattice (in particular, the c-axis parameter) with increasing Mg content. Strong UV with weak visible emission by PL studies establishes the sensitivity of the nanostructures yield, size and band gap to the intentional impurity. This tunability of the band gap of ZnO NWs with an intentional impurity could eventually be useful for optoelectronic applications.

Highly efficient fluorescent and biocompatible europium doped sodium zinc molybdate (NZMOE) nanoprobes were successfully synthesized via Polyol method. Non-radiative defect centres get reduced with Li⁺ co-doping in NZMOE nanoprobes. XRD spectra and Rietveld refinement confirmed successful incorporation of lithium ion and crystallinity was also improved with Li⁺ co-doping. The shape of phosphor is rod shaped, as determined by TEM. Significant enhancement in photoluminescence intensity was observed with 266, 395 and 465 nm excitations. Profound red emission was recorded for 5 at% Li⁺ co-doped NZMOE nanoprobes with 266 nm excitation. It shows high asymmetry ratio (~15), color purity (94.90%) and good quantum efficiency (~70%). Judd Ofelt parameters have been calculated to measure intensity parameters and radiative transition rates. In order to measure biocompatibility of the nanoprobes, cytotoxicity assays were performed with HePG2 cells. The fluorescence emitted from phosphor material treated HePG2 cells was also measured by Laser Scanning Confocal Microscopy. The bright red fluorescence in HePG2 cells treated with very low concentration (20 μg/ml) of phosphor material indicates that it could be a promising phosphor for biological detection or bio-imaging.