Lithium ion as growth-controlling agent of ZnO nanoparticles prepared by organometallic synthesis

ZnO nanoparticles were synthesized by adding solid Zn(c-C6H11)(2) to a THF solution of the lithium (sodium) precursor and octylamine (OA) as stabilizer. The proportion of Li (Na) was varied from 1 to 10 mol% compared to Zn. Two different lithium precursors namely Li[N(CH3)2] (series 1) and Li[N(Si( CH3)(3))(2)] (series 2) and one sodium precursor namely Na[N(Si(CH3)(3))(2)] (series 3) were used. Interestingly, Li precursors induce a modi. cation of the growth of the particles while, no effect is observed when Na precursors is used. Indeed, isotropic nanoparticles were obtained when Li precursors were used while nanorods were formed with Na precursor as already observed in the same experimental conditions without alkali-metal precursor. Observations by TEM show that as the Li/Zn molar ratio increases, the mean diameters of the nanoparticles vary from 3.7 +/- 0.7 nm to 2.5 +/- 0.4 nm, and from 4.3 +/- 1.0 nm to 3.1 +/- 0.8 nm for series 1 and series 2, respectively, while the length and the diameter of the nanorods are ca. 11 x 4 nm, for series 3. Interestingly, the consequence of the lithium induced size variation leads to a shift of the emission band in the visible range, from yellow to blue through white as a function of increasing concentration of lithium precursor. The intensity of this emission is strong enough to be clearly seen by the human eye.