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We synthesis different sizes of cadmium selenide quantum dots (CdSe QDs) and their linear and nonlinear optical properties. Size-controlled CdSe QDs are characterized by ultraviolet-visible absorption, photoluminescence, transmission electron microscope (TEM), and Z-scan techniques. Redshift was observed in the linear absorption and photoluminescence with an increase in the size of CdSe QDs. TEM images show the sizes of the QDs are 2.2 nm-4.9 nm. Bandgap tuning CdSe QDs of third-order nonlinear optical properties are investigated at 532 nm with an open aperture Z-scan technique using a picosecond laser. These CdSe QDs can be used as optical limiters.

ZnO nanoparticles doped with transition metal (Ag, Ni, Mn) were prepared by using co-precipitation method. Absorption spectra showed exciton peak for ZnO nanoparticles at 367 nm and for Ag, Ni, Mn doped ZnO nanoparticles at 328, 354 nm and 342 nm respectively. Photoluminescence dynamics showed shallow level-trap and deep-level emission where the intensity of deep-level trap increases with transition metal doping due to the oxygen deficiency. Nonlinear absorption measurements showed the two-photon absorption increasing with transition metal following the trend Ag > Ni > Mn when excited with 532 nm, 30 ps laser pulses. The transition metal doped and un-doped ZnO nanoparticles can be used as optical limiters.